1990 500SL ASR light issue advice needed please

[sean j g]

Hi as per the heading, my 1990 500SL has developed an issue, i replaced the distributer caps and rotor arms due to a slight misfire as the old caps were cracked, car now runs perfect but it now has a fault that the ASR light comes on when driving and the car goes into limp mode and won't rev, it could be complete coincidence i have double checked the caps and rotor arms fitment and they seem fine and are genuine bosch parts,but thought i would mention incase it is relatedto these being replaced, any advice would be much appreciated many thanks.

[Hereward]

What is the trigger event that causes limp mode and the ASR light to come on? Or are these issue present as soon as you start the engine?

I had a similar problem on my 1996 car that was caused by using gearbox kickdown. I fixed it by replacing the gearbox electrics (not as bad as it sounds). Your gearbox is different to mine but I wonder if the root cause is the same?

[sean j g]

Hi thanks for your reply, the fault occurs when driving along, when i stop and switch off then restart its fine again for a bit then the fault re-occurs, i have noticed however that the car doesn't seem to be kicking down like i think it should and stays in a higher gear when i hit the throttle pedal and just picks up speed gradually, so from what you are saying could this be a related fault, any info would be great thanks again for your help and advice.

[PositronicRay]

This imo, is the very best problem solving forum for MB R129s, some very enthusiastic and knowledgeable people post here.

[Zonergem]

No harm in also posting on Benzworld and MBClub.co.uk as well though, stating clearly the model year (chassis subtype ideally which for you should be 129.066) and the symptoms/trigger. More indies post on MBClub in my experience.

[Hereward]

sean j g said:

Hi thanks for your reply, the fault occurs when driving along, when i stop and switch off then restart its fine again for a bit then the fault re-occurs, i have noticed however that the car doesn't seem to be kicking down like i think it should and stays in a higher gear when i hit the throttle pedal and just picks up speed gradually, so from what you are saying could this be a related fault, any info would be great thanks again for your help and advice.

Sounds exactly like the issue I had. I cured it by replacing the "conductor plate" in my gearbox. However, I have no knowledge about your car's gearbox and I don't want to lead you down the wrong path.

The consolation for you is that your gearbox (722.3?) will have been used in thousands of Mercs of that era so I would expect a decent gearbox specialist will be able to easily diagnose/rule out issues.

Good luck.

[r129sl]

I would have a good look at the ABS/ASR "rings" and sensors. I have had to replace a front hub and a rear reluctor ring as these components have become worn by corrosion over time. On both occasions I had trouble with all the wheel speed sensitive systems: ABS, ESP, cruise control, speedo.

[BlueMR2]

Could have a problem with this unit, https://www.youtube.com/watch?v=_GCqdOT1jFg