ABS Brake Dash Light

[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. 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.

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.