ASR / ABS lights intermittently turn on

[infra]

Hi all,

As an FYI - I had read all I could about previous posts pertaining to ASR/ABS issues, so apologies if I have created yet another thread on the subject.

I'm still not clear what could be causing it. I do understand there isn't a single solution either.

I've got a 1991 500SL (Japan)

Symptoms:
-Start the car, the lights are off
-Drive the car until running temperature, the lights are still off
-Turn off the car and turn on the car a short while after (5-15 minutes), the ASR/ABS lights are on and will remain on until either A) I drive for 5-10 minutes, then they turn off or B) I rev the engine a couple of times then they turn off
-If I'm driving on a rough road (i.e. lots of bumps), the lights will come on like clockwork producing an effect of engine power loss (or slight breaking) for a very brief period of time (around the same time the lights turn on and then off)
-I was going down a bumpy road that was going downhill; I put the transmission in neutral and observed the RPM's... everytime the the ASR/ABS lights flickered on, the RPM's would jump anywhere from 500-1000 RPM's and come right down.


I've checked the battery via load test and checked the alternator and the battery and alternator are perfectly fine.

The next task I am thinking of doing is cleaning the speed sensors on all the wheels (I believe they are on all 4 wheels). What's unusual is that you would think the speed sensors were the culprit if the only time the lights ever came on would be on bumps on the road; but that's not the case above... as it also comes on if I shut off the engine, walk away for a few minutes, then come back and all of a sudden those two lights are on until I wait it out or rev the engine.

Any ideas/suggestions are greatly appreciated.

Thank you.

Nik.

[RedLiner]

Nik, firstly could you add your vehicle details and your location to your profile.

You've asked for a lot of information and we don't even know what R129 model you have!

[infra]

Apologies! It was late I guess.

I've got a 1991 500SL (Japan).

[merc-mark]

Hi there,
Have you checked the voltage across the top of the OVP relay? It's the one with the fuse in the top of it and located in the relay box in the engine bay, on the left side of the car (just under the windscreen) Voltage should be within 0.3v of battery voltage. By what you say, it sounds like the voltage getting to the ABS/ASR module is erractic.

Hope this helps.

Mark.