Jon has covered this a gazzilion times, but when it happens to you, the more information the better.

Got home from OKC and the bus would not come back up to ride height after lowering to unload. I had to use the manual position and level up the bus to get it in the garage.

This is a simple fix, if you have the parts and can be easily diagnosed by just swapping out the center position valve (right height) with one of the other valves to determine if the coil is the problem. Another easy way is to put 24 volts to the coil and see if it magnetizes. This is a 30.00 part and I now carry a spare coil and valve with "O" rings.

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Coil Part #641929 - 30.89

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Valve and Coil