I need an ABS expert

[mnichols]

I recently had the ABS light illuminate on my 1995 M3 track car. We setup the ABS test system and found a problem with the left front valve in the abs hydro unit. I replaced the unit and that solved the ABS light issue. The light now illuminates when I start the car and promptly goes out after self-diagnostics are complete. However when I take the car out on the road, I can lock up the tires. The ABS system is not modulating the slave cylinders.

I've checked the motor in the new unit, I can run it by connecting a jumper in the ABS relay socket. I've checked both ABS relays and they both work.

What could be so profoundly wrong with the system that the internal diagnostics are not finding the fault? I'm looking for ideas of where to look. Track days are coming up and I don't want to run without the ABS system.

[mnichols]

I have always been a strong proponent of DIY work on track toys, the more you work on the car the more you learn. But DIY has its pitfalls, typically the mechanic more than the car and it's parts.

That was the problem with my ABS issue. After trying everything I could think of to make the new ABS hydro unit work, I decided to try repairing the old one. There is a great thread on how to re-wire the solenoids in the ABS which is the typical failure mode. So I opened my old one and removed the foil wiring system and replaced it with 20 gauge wire. I did find one circuit that was open. With the new wiring, it now seems to have perfect resistance measures for each coil so I'm confident it will work.

I started to replace the new one with the old one and during the removal process found my problem. I had labeled each brake line with a number so that they would go back into the correct position on re-install. The mechanic (me) didn't read the labels correctly and put line 2 in line's 3 spot and vice versa. After correcting the plumbing the new unit works perfect, so now hopefully I have a spare.

You need to label things correctly, then pay attention to the labels when you rebuild!!!!!

[Manolito]

Everyone here has been humbled by our own mistakes - some of us more times than we care to count. Thanks for posting the solution.

[crashmy911]

I[ve got a problem with my abs also. When plugged into a diagnostic machine it reads pin 19 for the code. Does anyone have any idea what that is trying to tell me. the abs doesn't work and the light is on all the time.

[mnichols]

When I was working out the issue with my E36 ABS, I found this site that has a list of codes for the Bosch ABS.

List of the Fault Codes for the ABS/DSC Module

It will depend on the model of your car.