ABS Brake Dash Light

[0533]

I am getting an ABS idiot light on my dash. It is supposed to go out after you reach 4 MPH but it does not. I think it is a connection as it is not happening every time I drive off. Any ideas where I should look for a sensor or connection ??

[Jon Wehrenberg]

Bruce,

I haven't done this but I think there is a way for you to flash the ABS codes. I scanned my ABS system book once and saw there is a way to read the code.

FWIW mine will stay on if it has been damp or raining just before I drive. The next time I turn the bus off after driving a while and then restart the bus it will go out. I have never bothered to check why it is doing that because when I get to a place where I can mess with it, it is usually not lit.

[0533]

I have experienced this as well. I read my codes, nothing ABS related. Is there a sensor or fuse? Wires leads etc???

[Kevin Erion]

Bruce,
On that year they had problems with the sensors in the rear end. They have to remove the ring and pinion to replace the sensors. It gets little costly to fix!

[0533]

What is a ring and Pinion, remember you are speaking to a regular citizen here. I am heading to Prevost for my Tag tire upgrade and a few odds and ends should I have them look at this or live with it??

[merle&louise]

Bruce,

I have experienced the same problem with the ABS light coming on & off when it is raining or high humidity. It always goes off after the weather clears up and dries out.

[Jon Wehrenberg]

Bruce,

You will not read ABS codes where you read DDEC codes. If you go to the ABS owner's manual it will tell you how to read the codes. I have a switch next to my computer receptacle for my ABS.

[0533]

Where is the ABS booklet ? Is it in the big Prevost Box ?? Are you saying there is a switch next to the plugin for the DDEC reader that will allow ABS codes to appear on the print out.

[Jon Wehrenberg]

Bruce, Are you asking me where you keep your service manuals?

All I am saying is that the ABS, like the DDEC has a receptacle for a technician to plug in a reader. As an alternative there is a way to flash the codes without a reader. That procedure is listed in the ABS book. If you do not have a book like that in your coach documentation you can likely find it amongst the service manuals for your coach that you can access on line.

[0533]

Thanks Jon. I may have Prevost check this one when I am in Jax next week.

[Denny]

Bruce,
My ABS dash light was on all the time and never went out. I had it checked out and it was a driver's side rear sensor. As Kevin mentioned, the ring and pinion had to be pulled to access the sensor. Had it replaced at Prevost in New Jersey. There are front sensors also, and as I understand it, are not as complicated to replace as the rears.

When replacing one rear, have both replaced. The labor is just a little more to do two as to do one. As I recall, it was around $1500.

The newer coaches have a different system and is not as difficult to change but our vintage coach, 1998 chassis on mine, the rears are a PITA to work with and costly.

Denny

[0533]

Hello Denny,

That is expensive. The sensors are just that, they do not affect the function of the ABS system?? If this is so then I think I will get rid of the light.

Its interesting though that Prevost does not consider this light malfunction a possible defect and or recall item. I guess it is because it does not affect the ABS system but does cause us to ignore the possible problem. I do not think that GM could get away with this.

This idiot light will be going dark unless it is important not to.

[truk4u]

Bruce,

In your Prevost manuals there should be an axle manual such as Eaton that is labeled ABS. You can check the blink codes (toggle switch and light probably in the steering bay) and identify which part is causing the problem. I had to do this once and it identified one of the sensors. I reset the system per the manual and never saw the light again. It's easy to do, just count the light blinks in order and refer to the manual.

[0533]

I have looked at this switch for months now and wondered what it was for. That is really interesting. I will look for the Eaton manual and give it a try.

Very interesting. thanks Tom.

[Jon Wehrenberg]

Bruce,

If the ABS light is on, for whatever reason, the antilock braking feature is disabled.

If the system is disabled you have to control lockup. If you sense a wheel or axle is locking you have to release brake pedal pressure because a locked wheel has substantially less braking force than a wheel still rolling but just below the point of lockup.

Is this critical on our coaches? If you are driving in slippery conditions it could prove vitally important in an emergency stop. It may be less critical in the desert Southwest. Early XLs did not have ABS.

[0533]

Jon,

So what you are saying is that even if the problem is a sensor and the light is on the ABS system is not operating, it is disabled when an idiot light comes on.

So what happens if I am able to reset the light using the Eaton manual and the blinker in the steering bay?

[Jon Wehrenberg]

If the ABS light is out, such as by resetting, the system has been restored.

It is not like you do not have brakes when the light is on. You have the same brakes you always had, but control of the wheel lockup is now your responsibility, and not the ABS so the braking technique you must use is different.

When ABS is functioning, and you need to make a maximum performance stop, just slam on the brakes with all you have and allow the ABS system to control the braking force at each wheel. I have never locked up my brakes or needed that kind of stop in my bus, but on a car with ABS you slam on the brakes and hold your foot down as hard as possible. You will hear or feel the brakes pulsing as the ABS works to keep the brakes from locking up, but at their maximum effectiveness.

Without ABS you, the driver have to modulate the braking force to prevent wheel lockup.

Loss of ABS does not mean less or defective braking, just a change in your braking technique depending on whether your ABS is functioning or not.

[0533]

At least I know this needs to be fixed. It really is a safety item and should be a recall item. I am still surprised that Prevost can get away with this if it is happening to most if not all shells of our vintage.

[aggies09]

I am in Dallas at Prevost today having my sensor(s) replaced. Same issue as you described, light came on sporadically at first then just started staying on all of the time. Troy Moody at Liberty told me exactly what Jon just described as to what works and doesn't work when the idiot light shows up.

[Jon Wehrenberg]

Bruce....whoa.

The loss of ABS is not a safety issue. Not in the least. It only means you as a driver have a responsibility of controlling your braking, and that you have not turned that responsibility over to a computer.

A while back one of the car magazines did extensive testing on ABS using professional race car drivers. They determined that a skilled driver could do a better emergency stop without ABS compared to an ABS controlled stop.

Cars that have stability control turned off can perform better in the hands of a professional driver than with it turned on.

I know we are not professionals. But these systems are installed primarily to protect passengers against inept drivers. If your light is on I doubt if you could tell the difference between a stop you make without ABS (as long as you are sensitive to wheel lockup) to one in which ABS is employed. You just have to recognize the two different braking techniques required.

I'll let the professional truckers here, all of which I'll bet have driven with and without ABS, chime in.

[rbeecher]

Bruce,

Go back to Truk's post regarding the blink codes and then call Prevost tech support, they will walk you through running the ABS code test in about 5 minutes. The switch is in your steering bay and they will tell you where it is. On my '96 VOGUE with ABS, the light came on and Prevost quickly helped me determine it was the right front sensor, not the dreaded rear one inside the center of the rear axle. I took a 10mm wrench, removed the sensor, cleaned it and put it back in, problem solved.

I also agree with John with one exception, not having ABS, especially in a 45,000 lb plus rig will become a safety issue real fast if you find yourself in a situation where it is designed to keep the bus under control.

In race cars, we use a racing ABS set up which is not as sensitive as in a street car. The reason a pro race driver can modulate the brakes better in a street car is because the ABS system is set up for the presumed less sensitive foot and reflexes of a mere mortal. :rolleyes: The pro driver however, can easily sense the reaction of a street ABS set up before it comes on fully. A race car with a racing ABS calibration is also much faster around a track than one without ABS because the driver can brake later and deeper before a turn. :eek:

Richard Beecher
02 Marathon XLII 45
96 VOGUE XL for sale
C63 AMG Mercedes
E63 AMG Mercedes
Porsche RSR race car (with racing ABS)

[jimshoen]

I had the same issue. Had both drive axle sensors moved outboard. Prevost has an update kit to do this.

[0533]

I have just returned from Prevost Jacksonville for service. I had the ABS system checked. The code (273) read out that there was an over voltage. They reset the code and all was fine. The ABS light went out at 4 mph.

I headed out of Jacksonville and headed south, the voltage meter was reading about 29 volts which is what it normally reads. I had planned on stopping at ext 129 off 95 for diesel at the Pilot and say hello to Mike Kerley ($268 P/G), as I was heading off the ramp I noticed that my voltage meter on the dash was starting to hunt, hunting up and down by a few volts, the dash lights were dimming as well and hunting up and down the same, then all of a sudden the ABS light came back on, my guess is that the ABS computer sensed an over voltage again.

I filled up the bus with diesel and headed back onto 95 S. The voltage meter was still hunting, lights doing the same. I turned the genset on and in about a minute the voltage meter stopped hunting and dropped to 25 volts (from 29 volts) settled in nicely.

My question and thoughts: Is it possible that the Voltage regulator is not functioning correctly?? My reason is that when the Genset is running the voltage drops to 25 volts and the battery charging light comes on. Is this a sign that the regulator is not working correctly or is the output of the Alternator setting too high or not working at all??? I am confused.

Summary:

1.Left Jax: Voltage is 29 volts not hunting, ABS is normal all is well.
2. 200 miles later the voltage meter is hunting up and down, the ABS light comes on and the dash lights are also hunting up and down.
3. I turn on the genset the voltage meter stops hunting the voltage drops from 29 volts to 25 and settles in nicely, the battery dash charge light is on.

Anyone have a clue.

[phorner]

Bruce,

Do you have a battery charger for your chassis batteries hat would run off the generator?

Otherwise, I don't see how your generator running could influence the charge rate of your chassis batteries.

[0533]

That is interesting. I do have a charger that is on a timer, but should not be able to be charging during this time period we are discussing as it should have been in the off cycle. I will check this to see.

My Chassis battery charger is connected to my Engine block heater outlet which has a master switch on my dash for the outlet. My outlet switch for the Block Heater is on (the block heater plug is disconnected) and the Chassis battery charger and the timer are plugged into this outlet. My point here is that if the charger was on it would have been charging as a result of the inverter producing AC to the Block Heater Outlet???? It was not, but when I turned on the Genset the voltage dropped from 29 to 25 the dash chassis battery charge light came on and the lights stopped surging. Go figure.

[Ray Davis]

I would certainly turn off the block heat switch, to rule out the possibility that this is the source of the over-voltage.

IF it still happens, then likely a voltage regulator or worse the alternator are suspect.

Ray

[0533]

Hello Ray,

I have been speaking with Prevost about the situation. here is what they say.

When I am running down the road without the genset on the alternator is sending current to the Isolator that sends along power to both the chassis and to the house batteries. If the house side is calling for more power and either the regulator or the alternator is not functioning properly it has to increase the voltage to meet the demand . It is possible its increasing the voltage to the chassis batteries beyond their limits.

When I turned on the genset it satisfied the house battery requirements allowing the alternator to reduce it load and therefore reduce the load to the chassis batteries, from 29 volts to 25 volts.

Here is the problem, 25 volts might be too low and therefore triggers a battery dash light, which it did.

I was told to check the following:

place a meter on the field and ground of the regulator and check the output.

place a meter on the alternator and and ground and check the output of each leg, compare it with the regulator.

Check the output of the Isolator and see what it is producing, compare all 3.

It is possible that I need to adjust the regulator, down. It is possible that the alternator has a bad leg and the other 2 are working to make up the difference,

It is possible that I have a bad Chassis battery, i will check all

i will get on this in the morning and see what shakes out, I'll let you all know.

[Jon Wehrenberg]

There is a mix-up in this conversation between 120VAC and 24VDC. The two are not related.

First, If the engine is running the alternator(s) are charging the house and chassis batteries. Bruce has not identified what ones he is talking about.

Second, He has not indicated if the engine is running along with the generator. For example, if the bus engine runs and the voltage he is looking at is the chassis, and then turns off the engine, but runs the generator, the generator does not usually charge the chassis unless the chassis battery charger is turned on.

Unless the specific conditions under which voltages are being read can be described such as engine running, what voltages (house or chassis), what devices are functioning (charger? inverter?) anything posted here is apt to be speculation and only adding to the confusion.

[0533]

I am sorry about that, i did however explain the condition in an earlier thread. The engine alternator should be charging both the house and the battery, as it running

When the engine is running at highway speeds and after about 3 hours of running the voltage meter started to surge, hunt up and down and the dash lights go up and down as well. Once this happened the ABS light came back on (ABS had been tested at Prevost and showed an over voltage). the voltage meter was reading 29 volts

So i turned on the genset (it had been off and the house batteries were the only source suppling all DC to the inverters) and the voltage meter stopped hunting, the voltage meter dropped to 25 volts and the battery light came on, either showing an under voltage.

I am going to test the alternator, the batteries , regulator, and the Isolator to see what each is producing.

I now have a vanner trouble shooting manual to guide me, Prevost sent it along today.

[Jon Wehrenberg]

As a single alternator coach (I know that because you said you have an isolator) your alternator voltage regulator should not vary the voltage depending on what level of charge your batteries have.

The role of the voltage regulator is to maintain a set value for the output of the regulator. On a 24 volt coach it should be around 28.2 to 28.4 volts.

The equalizer(s) should maintain a relationship between the 12V and 24V batteries in your coach, the 24 volt being two 12V batteries in series. The 12V side should be exactly 50% of the 24 volt side +/- 1/2 volt.

All the isolator should do is prevent current flow from either set of batteries to the other. The alternator input to the isolator should pass through the isolator to both sets simultaneously, but never from one set to the other. Think of the isolator as an air hose coming from a compressor (alternator) and the isolator is the "tee". From the tee the air hose goes to two tires (think of the house and chassis batteries as tires.)

As the compressor runs its maximum pressure is 28.4. The air flows through the "tee" into each tire until each tires has 28.4 at which point that value is maintained. If one tire loses its pressure, because the "tee" functions as a check valve air from the remaining tire cannot flow into the other, but air from the compressor can flow into the tire with less air. As you can imagine the regualtor value is set at a point that will not harm the batteries. but just like trying to put 125 PSI into a tire from a compressor that will only put out a maximum of 125 PSI your alternator / voltage regulator is doing the same thing. It will use a lot of amperage if your battery voltages are down, but reduce the current as it approaches the set point. What will not vary is the set point for voltage unless you have an enormous load such as completely dead batteries and then it might pull the voltage down a little because the current draw (amperage) is approaching the alternator maximum output.

Sorry for the goofy analogy, but it helps understand a few things. First, the output of the alternator in volts is a constant as determined by the regulator. The isolator merely serves to allow current flow in one specific direction. It has nothing to do with voltages. Equalizers only dstribute incoming voltage to batteries such that the relationship of the 12 and 24 volt sides is maintained within 1/2 volt.

It appears you have intermittent voltage regulator or alternator function. One of them is going bad. If you have an on-board chassis charger, let what is going bad puke and then fix it. Trying to chase an intermitent problem takes time and yields nothing but frustration. Assuming the problem is one or the other is a very expensive way to deal with it.

[truk4u]

Bruce,

For what's it's worth... My 97 Marathon did not like the chassis battery charger running off the inverters. If I unplugged and forgot to turn off the 24V battery tender I installed, running off the block heater plug, all the lights in the bus would pulsate. Simple solution for me, make sure the block heater circuit breaker in the bedroom was turned off when unhooked from shore power.

[phorner]

Seems weird to me that they would wire an engine block heater circuit to run off the inverters....

Sure way to drain the batteries FAST!!

[truk4u]

I agree Paul.. Maybe that's why there was no button on the dash for the AC block heater, only the circuit breaker in the bedroom panel.:rolleyes:

[Jon Wehrenberg]

Apples and oranges.

The pulsating DC voltage should have nothing to do with what 120V loads are on the inverter. And I agree, the block heater among other things should not be running through an inverter. But if it is, that's just about as nonsensical as running a battery charger through inverters. That would be like lifting yourself off the ground by pulling up on your socks.

[0533]

Thank you Jon for the careful review of the single alternator system. I am carefully considering what you have said and planning on attacking the problem this morning.

What I cannot understand is how I am going to be able to run my multimeter cables from the back of the bus to the Aux Air line hose outlet in the steer bay all the way up front to make the proper contacts??

[truk4u]

Bruce said his dash lights were hunting up and down, similar to what mine did and that's why I made the comment, if it was even read.

I'm not making this crap up, it is what it is!

[truk4u]

Paul,

In thinking more about the block heater running off the inverter, with the Marathon, that would be no big deal. It would run 1 cruiseair for 4+ hours and 2 cruiseairs for about 2 hours. Not much difference in the amp pull for the block heater and a cruiseair, my Liberty shows 14 amps for the AC block heater.

This should drive A-1 crazy.:p

[0533]

The Block Heater AC Outlet in the back of the bus is a regular GFI outlet. There is a block heater with a plug that is not connected to the outlet, but rather wire tied next to it in case I wanted to plug it in. There is a breaker switch above thae dash for "Engine outlet". I keep it off unless I am using my Chassis battery charger that is also connected to the Engine AC outlet GFI receptacial.

I have not noticed the surging problem while having the charger on during engine operation, driving along.

What bothers me is that I can start a trip with absolutely no issues at all, but after about 3 hours began to experience a surge in the voltage meter, dash lights pulse etc.

I am being told that because the "House Batteries" are requesting a charge from the Engine alternator to keep the house batteries at a proper level to service the house draw.

If the Alternator or the regulator is not functioning correctly it appears that one or the other is creating an over voltage (which is tripping off the ABS computer my other problem) .

Marathon mostly installs single alternator conversions with a regulator Isolator and Vanner Load balancers.

Prevost said that it is one or possibly 2 of 3 problems:

1. Regulator is producing an over voltage and either needs to be turned down, or replaced, hopefully it is the regulator.
2. It could be a bad chassis battery, one bad apple causes a big draw.
3. A bad leg on the alternator, causing the other 2 to create more voltage to provide enough demand to the house batteries (isolator).

The final condition is the fact that the generator reduces the voltage dash meter from 29V. to 25V within 1 minute after starting the genset.

But when this happens the dash battery light comes on showing what I believe is an under voltage, go figure.

I am heading over now to start the inspection and testing process, will report, have a cheat sheet for testing provided by Prevost service manager.

[truk4u]

If you have the single 270 amp 24v alternator, keep in mind that you have 2 equalizers, one for the chassis and another for the house. The house equalizer on mine was behind a panel on the forward bulkhead of the house battery bay.

[Ray Davis]

Please consider turning OFF the battery charger when driving and see what happens. Tom's experience seems to indicate this can be a problem, and if you have that charger on while driving, then it's running off of the inverters, and Tom has indicate he experienced similar issues in his Marathon.

Some electronics does not like the modified square wave which comes out on an inverter.

It *may* be that when you turn on the genset, that now you're getting a better AC signal to the charger, and things settle down?

It certainly may not be the case, but it's trivial to isolate and rule this one out. Turn off the chassis charger, and drive it.

Ray

[Jon Wehrenberg]

Bruce..........

"I am being told that because the "House Batteries" are requesting a charge from the Engine alternator to keep the house batteries at a proper level to service the house draw."

Bogus.

"If the Alternator or the regulator is not functioning correctly it appears that one or the other is creating an over voltage (which is tripping off the ABS computer my other problem) ."

That sounds very reasonable, with my money on a bad regulator.

"The final condition is the fact that the generator reduces the voltage dash meter from 29V. to 25V within 1 minute after starting the genset."

Here is where the communications are breaking down. Is the engine running when you start the generator? If so, which voltage are you describing? House or chassis?

Let's do a quick system overview. When your engine is running, with a properly functioning alternator and voltage regulator, both the house and chassis batteries are being charged and because the alternator is so large in terms of output it can handle almost any resaonable load and you will see no difference in the voltage.

With the engine still running, if you start the generator, and the inverters have been left on, the generator power is seen by the inverters, and both the inverters begin to function as battery chargers for you HOUSE batteries.

The alternator voltage regulator should not see that charging voltage because the isolator prevents house voltage from flowing back. Since the voltage regulator battery sense circuit is detecting chassis battery condition the alternator continues to function and should continue to put out 28.4 volts.

So under what specific conditions does the voltage drop to 25, and is this house or chassis voltage?

The dash light fluctuation is an indicator the voltage is varying. As it goes up and down so does the light intensity. The fact that it is dash lighting tells me the variation at that point is with the chassis side of the system. Does the house lighting do the same?

[0533]

Your right, there are 2 equalizers, mine are all on the bulkhead just inside the engine Passenger side door above and behind the chassis battery shut Off switches.

I have the 24V Alt, a regulator inside the main Prevost flip up box above the engine, an Isolator (Big Blue Cylinder) 2 equalizers, and of course 4 chassis batteries and a vanner box that shows Batt Hi, batt Lo, balance etc.

I did some testing today, here is what I found: I ran the engine at 1000 rpm, with load, lights, dash air, blower motor, etc.

1. All batteries read 13.2/.13.7 this was done while the batteries were disconnected.
2. The batteries did need topping off. some low cells, added distilled water.
3. Regulator reads at FLD/Alt between 6 to 7 Volts.
4. Isolator reads 28.2 at both sides, Chassis and House.
5. Both equalizers read 28.2 volts

I then turned on the Genset: Still had load on Chassis batteries, 1000 rpm with lights, air blower motor on.

1. Batteries are all reading fine,
2. Regulator at FLD/Alt reads -.18 V (cannot understand this reading, did it several times
3. Isolator reads between 24.7 and 25V on the Chassis side, 28.4 on the house side,
4. The dash light for battery charging was on.

There was no hunting at all, but I had not run the bus more than 30 minutes.

I really do not know what is wrong, but am wondering about the effects of the Genset on the chassis side.

The dash voltage meter seems to read correctly in all cases, very close.

I also tested the voltage meter by touching each end together, .5 Ohms lose.

[Ray Davis]

When you tested, was the 24V battery charger running via inverter?

Why do I stress this?

The regulator will regulate what is coming out of your alternator, NOT out of your extra charger that is essentially in parallel with the output from the engine charging system.

IF it does not like the modified sine-wave from the inverters, it's possible that the charger could put out a funky 24V, with a large AC ripple. I don't know, but this seems to jive with Tom's experience.

IF you have a large ripple right on the battery posts because of the charger, your dash is going to see this.

28V out of the regulator is fine.

So, without trying muddy the waters, did you turn off the battery charger? IF so, did it behave as expected then? If it's still misbehaving, then you've ruled it out, at least.

Ray

[0533]

When you tested, was the 24V battery charger running via inverter?

Why do I stress this?

The regulator will regulate what is coming out of your alternator, NOT out of your extra charger that is essentially in parallel with the output from the engine charging system.

IF it does not like the modified sine-wave from the inverters, it's possible that the charger could put out a funky 24V, with a large AC ripple. I don't know, but this seems to jive with Tom's experience.

IF you have a large ripple right on the battery posts because of the charger, your dash is going to see this.

28V out of the regulator is fine.

So, without trying muddy the waters, did you turn off the battery charger? IF so, did it behave as expected then? If it's still misbehaving, then you've ruled it out, at least.

Ray
No i took it out of the system for the entire test.

[0533]

Bruce..........

"I am being told that because the "House Batteries" are requesting a charge from the Engine alternator to keep the house batteries at a proper level to service the house draw."

Bogus.

"If the Alternator or the regulator is not functioning correctly it appears that one or the other is creating an over voltage (which is tripping off the ABS computer my other problem) ."

That sounds very reasonable, with my money on a bad regulator.

"The final condition is the fact that the generator reduces the voltage dash meter from 29V. to 25V within 1 minute after starting the genset."

Here is where the communications are breaking down. Is the engine running when you start the generator? If so, which voltage are you describing? House or chassis?

Let's do a quick system overview. When your engine is running, with a properly functioning alternator and voltage regulator, both the house and chassis batteries are being charged and because the alternator is so large in terms of output it can handle almost any resaonable load and you will see no difference in the voltage.

With the engine still running, if you start the generator, and the inverters have been left on, the generator power is seen by the inverters, and both the inverters begin to function as battery chargers for you HOUSE batteries.

The alternator voltage regulator should not see that charging voltage because the isolator prevents house voltage from flowing back. Since the voltage regulator battery sense circuit is detecting chassis battery condition the alternator continues to function and should continue to put out 28.4 volts.

So under what specific conditions does the voltage drop to 25, and is this house or chassis voltage?

The dash light fluctuation is an indicator the voltage is varying. As it goes up and down so does the light intensity. The fact that it is dash lighting tells me the variation at that point is with the chassis side of the system. Does the house lighting do the same?
Hi Jon,

The engine is runnng when i start the genset.

The voltage is the dash meter for the chassis side, 29 dn, to 25.

The chassis batteriesVoltage meter shows 25V when the genset is on, engine running,

The bus lights, dash flucuate not the house side, no effect.

Please see my finding below 3 threads down, it might offer some clues.

[Jon Wehrenberg]

Bruce,

Either the regulator or the alternator is puking. That's my guess.

When the engine is running at high idle, connect the tester to the 24 volt post and a ground on the chassis batteries. If everything is charging you will read about 28 volts.

Then do whatever you do that causes it to drop to 25 volts.

Leave the tester connected and reading your chassis battery voltage. Jumper between the Positive and Field terminals on the regulator. While you are doing this observe the voltage on your tester. If you have a regulator problem you will see the voltage start to climb. Do not leave the jumper in place. All you want to note is if placing the jumper in place causes the voltage to go up. If the voltage rises the regulator is bad. If not suspect the alternator is bad.

You will have unregulated voltage with the jumper in place and after a few seconds that voltage has the potential to climb quite high so don't leave that jumper on if the voltage climbs past 28 volts.

The inverters should have nothing to do with the output of the bus alternator because the isolator should never allow the voltage level of the house batteries to be "seen" by the voltage regulator, HOWEVER>>>MAKE CERTAIN YOUR CONVERTER DID NOT ALLOW YOU TO CONNECT BOTH BATTERY SETS SUCH AS TO ALLOW JUMP STARTING IN THE CASE OF DEAD CHASSIS BATTERIES. IF SO MAKE SURE THAT FEATURE IS NOT ENGAGED. IF THAT FEATURE IS ENGAGED DISENGAGE IT.

[0533]

Hello Jon, I plan on following your directions today and do the test below. Question: The Regulator is labeled FLD. & Alt side by side, are these the 2 you are suggesting I jump???

Regarding your question about the battery Boost dash button on my Marathon. i believe that I do have the ability to connect for short periods of time the house batteries to the chassis to start the bus when the chassis batteries are down??? I am not sure how this accomplished in the system.

Jon Writes: Leave the tester connected and reading your chassis battery voltage. Jumper between the Positive and Field terminals on the regulator. While you are doing this observe the voltage on your tester. If you have a regulator problem you will see the voltage start to climb. Do not leave the jumper in place. All you want to note is if placing the jumper in place causes the voltage to go up. If the voltage rises the regulator is bad. If not suspect the alternator is bad.

[Jon Wehrenberg]

"Regarding your question about the battery Boost dash button on my Marathon. i believe that I do have the ability to connect for short periods of time the house batteries to the chassis to start the bus when the chassis batteries are down??? I am not sure how this accomplished in the system."

I'm not familiar with Marathons, but you do have to make certain you are not connecting the house and chassis batteries. Otherwise the inverter input to the house batteries is seen by the voltage regulator through that jump start circuit, and the two sets of batteries are not isolated.

I don't think you have them connected, but I want to be sure because some of what you are seeing does not make sense to me.

[0533]

Hello Jon,

I jumped the Regulator FLD. and Positive and saw rapid increase in Voltage from 28 to almost 34 in a few seconds, quickly removed the jumper (just touching the 2 connections) and the voltage returned to 28V again. I will order and install a new Regulator in the morning.

[phorner]

Bruce,

I performed the same test and got the identical results.

A replacement voltage regulator solved the issue for me.... just wanted to give you a vote of confidence in your diagnosis....

Good luck!

Paul

[0533]

Paul, where did you purchase the Regulator and what did it cost?

[Jon Wehrenberg]

Bruce,

If your bus was putting out 28 volts when you did the test all you know is that both the regulator and the alternator were both working when you started the test. The time to do the test is when the chassis voltage drops down to 25 or 26 to indicate something is not working.

You seem to have an intermittent problem, somehow occuring after a period of time. When you notice the voltage drop thats when to run that test. You are almost free of concern because unless you run very heavy chassis loads, if your alternator or regulator stops functioning, you can run the generator plus turn on your chassis battery charger.

Paul had an intermittent problem and he also has a chassis battery charger so when his system finally failed to work he isolated the problem and cured it with a regulator. It could just as easily been a bad alternator, but until the system failed so the test could be preformed he could only speculate.

In the meantime just find a shop that can rebuild the alternator and locate sources for a new or repaired regulator so when the voltage drops again you can test and determine what has failed.

[0533]

Good morning Jon,

I tested the output under load, 1000 RPM's and with light, blower and air on, the Chassis voltage meter was fluctuating when I did the test. I think that the problem is always there, but gets worse as I was driving along, as time passed, I was draining down the chassis batteries or something???

I guess my question would be if I conducted the test you suggested and the voltage increased is the regulator not malfunctioning or not???

I plan on getting a regulator today and install it and do the test again.

While I was at Prevost they did suggest a few upgrades to my engine compartment. See following below:

1. Pulley tension upgrade kit that includes a change/move of the oil fill a tensioner and a new larger diameter oil line from the Alternator for increased flow/capacity. I was told by Prevost that the company that rebuilds the Alternators will not stand behind them unless the oil line upgrade (larger diameter) is installed. They also wanted me to have a separate ground strap installed from the Alternator to the chassis. They said that the buildup of scale/rust between the mount for the alternator develops scale and can cause a poor ground for the alternator.

[Jon Wehrenberg]

All the test with the jumper does is eliminate the regulator from the system. You in essence by-passed the regulator and as you saw you had an unregulated alternator output.

Having said that it is my opinion (nothing more than an opinion) that the belt tensioner is an unnecessary expense as long as the belt tension is adjusted properly. The oil line may be a good upgrade, but I don't know that for a fact. Being assured that the alternator has a good ground is critical.

Don't spend any money for an alternator or regulator until you have the alternator output stop. Then check the regulator / alternator as you did. But in the meantime remove one of trhe alternator bolts, make certain is is clean and totally free of scale and rust, not only on the bolt and nut, but on the surfaces it contacts and reinstall it. If the ground was in fact your problem that should solve it. I'm not sure it will solve your problem, but start with the cheap easy stuff.

[phorner]

Bruce,

Jon is 100% correct in that I waited until mine "failed" before performing the test on the regulator to confirm that the regulator was bad.

I also was having an intermittent low chassis battery voltage problem that would usually cure itself within 20 to 30 minutes of driving. I did not have the ABS light issue that you describe, just the battery light on the dash coming on and the voltage reading on the gauge.

So, when mine finally went, I performed the regulator jumper test as Jon described while the failure was present, which confirmed that I had a bad regulator. This test is only meaningful if performed while the low voltage problem is present.

I got my replacement voltage regulator from Advance Auto Electric in Port St. Lucie. Cost was around $200. They can also re-build your alternator if need be. Their number is 772-337-1280

[0533]

I think it is possible that mine is about to fail and decided to replace now and see if it makes the difference, process of elimination. I am no rocket scientist and might well have to replace everything before I figure out the real problem.

I received the new regulator today, it is a little different has five connections the first 4 are the same, Ground, Field, Battery, Ignition plus a 5th for Sense. Which makes non to me so I plan on forgetting this one.

The face is different as well, black poured in plastic material covering over the Mother board I guess as apposed to silver metal cover.

[phorner]

Bruce,

Sounds to me as if you may not have the correct regulator. Mine was an exact replacement.....

[0533]

I was told by Prevost that this was the replacement for the older style.It is model #19020413 MFG date is 2005 maybe it is not new but I paid $181 Big ones. I have just taken a closer look at this regulator and have noticed that it is a 12 Volt not 24 Volt regulator, my old one is a Delco Remy 24 Volt version, I think I need to call Prevost.

[0533]

I have had an ongoing problem with my dash ABS light coming on. It appears that when I had my over voltage issue it tripped the 12 volt circuit in the ABS module and kicked it off. When the light is on there is no ABS controlling the braking system on our buses, no matter what the actual problem is.

I had the ABS readout computer attached and it said that I had two issues, an ABS over voltage and a right rear drive axle sensor failure, or sensor wire connection failure.

The tech preformed a check of each sensor by activating a signal that would create a clicking sound at each sensor. All sensors answered the signal with a clicking sound, in other words they responded as though they were being activated under real world conditions.

This was done on Thursday afternoon. When I backed out of Bay #2, I decided to go for a spin down the road to see if the ABS dash light would go out after I exceeded 4 MPH it did not.

On Friday morning when we had the Bus up on the lift to inspect for air leaks, change out the Air system water filer cartridge and take a look at the Rear axle ABS sensors and do an electrical check directly on them to see if the voltage was correct. They pulled off a red connection, checked the sensor and cleaned and replaced the connection on the one that readout as a failure. I repeat they disconnected the sensor wire connection, cleaned it off and replaced it.

They also said that it would take 8 hours to replace the sensors and its a big expensive pain in the ass, try it again and see if the light stays off this time.

I left out of Prevost car yesterday with the light back on for the first 3 hours of my trip. I left the highway at Ext 129 for the Pilot, filled up and headed back to 95 south for Jupiter. The light was out and never came back on.

I am now guessing that the ABS system or the connection at the rear wheel is at fault. (hope so anyway)

When Rockwell designed these sensors and made its plan for their introduction in such a deep down location in the axle I do not think they envisioned the sensor would easily fail or ever fail. I do however see how the connection and the wire could fail at the axle as it is open to the elements dirt, grease, garbage of all kinds can gather at the connection to the axle, this is where I see problems with the ABS.

Conclusion, before allowing Prevost Car to replace these sensors see if a computer test of each sensor creates the all important clicking sound at each location, if it does take the connections apart and clean them before committing to a sensor replacement. i could be wrong here but it does not make much sense that the failure would always be at the internal sensor its self in all cases but rather the more exposed locations along the path back to the ABS computer.