ABS help

[RedTRex]

ABS light stays on when car is started.

Came cross this site with troubleshooting steps.

http://www.e30zone.net/e30zonewiki/i...p/ABS_Problems

I followed the steps:
- I have Ohm'd everything out - no issues,
- I have a second set of relays for top of unit - no change.
- I don't have a spare overvoltage relay, so I pryed the cover off this one and plugged it in, it actuates when the key is turned on, so I assume it is okay.
-
I think the brain box bad. can anyone confirm or have other ideas.
Thanks

[jlevie]

The link doesn't work, so I can't see what troubleshooting steps you've done, but here is my quick guide to diagnosing ABS problems.

Troubleshooting the ABS system isn't very difficult. It is a stand alone
system that only gets input data from the brake light switch, wheel sensors and
system power. The parts of the system are the ABS module located next to the
steering column, the ABS relay mounted above the ABS module, the ABS unit in
the left front of the engine bay, and a wheel speed sensor at each wheel.

If the ABS light comes on with ignition, but doesn't go out when the engine
starts, a wiring problem, bad module, or bad ABS relay are the likely
candidates. A failed or weak alternator will also cause this because the
system voltage won't rise enough. There is a fusible link inside the ABS relay
that can be blown. The relay can be repaired, or better yet replaced.

If the ABS light comes on when you turn on the ignition, goes out when the
engine starts, and then comes back on before the car is moving the cause could
be a bad module, a bad ABS unit, or a wiring fault.

If the goes out after engine start and only comes one when the car is moving,
there's a problem with one (or more) of the sensors. The simple test to find
out which sensor(s) is the cause is to disconnect all but one of the sensors
and drive the car. If the light comes on, that sensor is sending a speed
signal to the ABS and is good. Repeat with each other sensor to find the
one(s) that don't cause the light to come on. Since the ABS module has no
speed input besides the wheel sensors, if only a bad sensor is connected the
module can't tell the car is moving and thus doesn't fault on missing speed
signals from the other wheels. Once a bad speed sensor is found, if a new
sensor still doesn't work, there could be a wiring fault in that circuit or a
bad input channel in the ABS unit.

[RedTRex]

I saw your troubleshooting guide, the linky - which is now dead ...... had more steps for troubleshooting if ligth stays on all the time . e.g. Resistence values and where to look....

So I am down to think ABS brain...can anyone confirm?

[jlevie]

I can't tell what your symptoms are, so I hesitate to make a suggestion. Could you elaborate on what you are seeing?

[RedTRex]

I can't tell what your symptoms are, so I hesitate to make a suggestion. Could you elaborate on what you are seeing?

I thought I made that pretty clear in the above posts........



anyway, I was at the pick-a-part today and grabbed an ABS brain and OV relay......swapped both in just cuz' and my ABS light is now gone.....yay.

[RedTRex]

Update. ABS light started coming on again after driving off.

Following your procedures above jlevie, I disconnected all wheel sensors and found the RF to be bad, replaced with a spare and it is functioning 4.0 again.

Thanks for the great troubleshooting guide!
RT

[nmlss2006]

Link: http://www.e30zone.net/e30zonewiki/i...p/ABS_Problems

[nmlss2006]

And.. no solution. I have known good power on pin 20 @ C101. ABS light stays on. Would it really be the resistor in the 'silver' 6 prong relay at the ABS pump? this is a late car - 318iS - and I tried swapping the relais with one from a junkyard with no change in symptoms.

[nmlss2006]

Self following up: voltage inputs at hydraulic unit are OK. Relais seem to be OK. Light comes on at key on run and stays on no matter what. Is it safe to assume that the next step is try to swap ECUs?