1992 500SL ASR System Problem

I started having a problem with the ASR system on a 1992 500SL. I was driving on the highway when the ASR sensor light came on and the car defaulted to a "limp home mode": The engine output power was reduced and I was able to make almost home; after exiting the highway and reducing speed a red light, the battery light came on, and the car completely stalled. I restarted the car and the ASR light was off and the car drove normally home.

Two motors relating to the ASR system were replaced by the service shop: ($ 1,500 Parts & Labor). The car was running fine for two months then the ASR problem returned. The repair shop then replaced the ASR sending unit: ($ 680.00 Parts & Labor). Days after the sending unit was replaced the ASR problem continued to occur poradically.

The shop then installed a brand new electrical accelerating unit (a very expensive piece of computer hardware: ($ 2,000 Parts & Labor) in the hopes that the computer was causing the ASR sensor program to trigger in error, but the problem continues to occur.

The original electrical accelerating unit was reinstalled and I was credited for the cost of new computer module; thank god. The over voltage protection relay was also tested with a new unit but the problem persisted.

The repair shop has tested the car for the last few days, and according to them the problem did not returned. The shop owner told me that he drove the car all week without any ASR problem.

I picked up the car on Friday, March 4, 2003 and a mile from the repair shop the ASR console light came on, the car began the process of reducing motor output power and when the car speed reduced below 20-25 miles the battery light comes on, and the car completely stalls. This happened five times before I was able to make it home. I have to turn the car off, restart the car the light goes off, few minutes later the light comes on again.

I don’t believe the repair ship did anything during the time the car was at the shop, they also informed me that the ASR module was only install in the SL for two years 91-92 and then discontinued, and that Mercedes has very little technical information on repair procedure for the ASR in this model year. I believe it’s not true; I’ve seen the ASR system on all SL since 1992.

I think that they don’t have the technical expertise to isolate the problem, and they may have changed unnecessary parts at will in the hopes that one of the parts will resolve the ASR problem.

So far I’ve spent over $ 2,000 in parts & labor and the problem is the same as day one. I am temped to take the car to an authorized dealer for repair, but I think the shop should fix the problem or refund me for the work I’ve paid to date.

Has any one come across an ASR problem system similar to mine? Why would the battery light be an issue with the ASR system?

Any information could you provide would be greatly appreciated. I am concerned that this is going to be one of those problems that will haunt me for a while.

Your symptoms are consistant with needing your Wiring Harness replaced.
The insulation on the wiring starts degrading over time, eventually falling away from the wire completely in some places resulting in false signals. It seems that high heat quickens this process, when this happens the engine electronics start having problems, like what you are going through.

Do a search (upper right button) for "asr limp mode" and you will some good info on this.

This is a common issue on 500E's as the under hood temps are a little higher due to less air circulation space.

[spinedoc]

I had the same exact issue with my ASR. At first it was very intermittent. After getting motor mounts done the wires finally gave out and the ASR ligth was on most of the time. Once the harness was replaced I was good to go.

On these early years the wiring harness in this area was made badly, they have a tendency to deteriorate and become brittle, causing all kinds of weird problems.

Have the dealer or a good indie shop take a good look at the wiring harness.

Thank you for you help, I will take the car back on Monday and advice those weasels to test and inspect the parts you have described. I don’t believe that I should paid for additional parts, if the misdiagnosed the problem and probably installed expensive parts that were not required.