Over the past year my ASR light would come on occasionally and I could resolve it by restarting the car, a "95 S500. Lately the light will not go out and the throttle has about 8" to 10" of free swing before the engine will respond. and lthe cruise does not work either. I had it to my local MB dealer and he changed out one computer without any result and he eliminated the others. He changed the throttle control without effect and finally gave up. (Says he has 3 other cars of same vintage with same problem- can't figure out how to fix them either.) Car can be driven but have to let up on the throttle to get it to shift. Very awkward to drive and probably not very safe. What can I do with out spending $4000?

 

What makes you thinking, that spending $4000 will get your running?
Finding qualify mechanic for modern computers with wheels is not easy.
Posting your location might help?

 

This car is in SE South Dakota

 

Hi,
Please clarify symptoms and exact actions taken.
8 to 10" swing? What does this mean please Freeplay?
and he eliminated the others. What does this mean please?
Which computer was swapped out and why did the dealer think this was the problem? Hope he didn't bill you when it failed to fix!!
What fault codes are showing? If you have already paid the dealer should be able to give you this info.
Current mileage?
What other symptoms (if any) are there. e.g. did the cruise just stop working or did it start to misbehave.
Whats this about having to let up on throttle before the behicle will change gear?
I love resolving these sorts of issues but you need hard (real) data.
Any other pertinent facts. 3 other vehicles in your local dealership with the same problem! Sounds odd! Sounds like the dealer needs to send there sparks on an MB course.
Stuart.

 

Your car is in "limp mode" when it does what you're describing. Try switching the ASR off manually everytime you start the car and see if that prevents it from going into limp mode again. The ASR may be the culprit.

My car will do this if I do a lot of tire spinning. Dyno runs will cause this as well. Also, spinning on snow or ice. I suppose a defective ASR system will cause it too.

 

Hi.
I agree with Lugnut that the vehicle is in "Limp" from the pedal travel and gear change behaviour symptoms.

I was looking for an improved definition and specifically any other indicators / symptoms which may not have been reported.... without providing clues to the answer.

Since as I understand it an MB trained dealer has failed to resolve this problem we must ASSUME that the problem needs CAREFUL consideration. If the problem were common to MB or the Model I'm sure that MB would have fixed it. 3 other vehicles with the same problem doesn't sit comfortably however with this assumption!!

For the vehicle to go into this mode one (or more) of the input signals to the "system" must be out of limit. Unfortunately a number of system modules are all linked through the vehicle databus (electronic throttle / cruise / ABS etc) and a fault in any of these can impact others in apparently strange ways. In reality the interaction between systems exists for a reason (logic) and can assist in unravelling problems.

Unfortunately knowing that the system is in Limp doesn't assist in determining the ROOT CAUSE of why the system has shut down.

The fact that the ASR warning light is illuminated suggests that the fault COULD lie with the ASR components....equally it could be an input into the ASR from another system that is out of limit.

In order to avoid doing all checks over again we need to understand what the MB guy did, and why. For instance did MB engineer check the throttle potentiometer and wheel sensor outputs (to name just 2) before changing the "Module" (which one?). Were the Outputs / Inputs within the permitted range? If I had been asked to pay for such an expensive unit without effecting a repair I would want to know why it had been changed. However it is not good enough to assume appropriate checks were carried out since Root Cause may be overlooked.

Since this MAY be an age related issue (mileage / useage eg everyday vs just occasionally) did MB check the circuit ground points?....What could be common between the 3 other vehicles which exhibit EXACTLY? the same problem?

I am not a MB guy however I am a QUALIFIED PROBLEM SOLVER in Electro / Mechanical systems and ENJOY the challenge of resolving problems of this type.

Once I have some ADDITIONAL info I will consider the best course of action to identify the CAUSE.

A good place to start on older vehicles is often SUPPLY VOLTAGE. If this Input is out of range the system shuts down. A POTENTIAL ROOT CAUSE COULD BE DIRTY CONTACTS ON THE SUPPLY RELAY (causing low voltage) which may explain why the system could be coaxed into working for a time after a restart........ but one should NEVER JUMP TO CONCLUSIONS.

Typical Structured (vs Get Lucky) steps to problem solving.

1. Collate symptoms (Fact vs Fiction / Intermittent vs Continuous etc)
2. Determine a test regime to gain additional info with a view to reducing the possibilities.
3. Rank possibilities
4. Demonstrate that the problem can be turned ON / OFF.
etc etc.....

Subject to the info I requested I will review the wire diagram and suggest what checks and actions may resolve this problem.

 

I had my tires rotated and balanced a while ago and this happened. It kept going into limp mode and the ASR light would come on. The tire guys did something. I don't know exactly what, but the ECU had to relearn something. It just took a few keystarts and some miles then everything was okay. Just like the other stuff I listed. This particular condition doesn't set a fault code, so the brainless dealer techs wouldn't be able to figure it out unless they noticed the ASR light.

I think what you're proposing is overkill at this point. I'm not saying it's bad info. It's the ASR system that's putting it in limp mode. The ASR light is on. I know other things will put it in limp mode, but other things won't turn the ASR light on. This is a common problem. I would propose disconnecting and reconnecting the battery if you want to hurry things along. If the easy stuff doesn't resolve the problem, then go into days and days of troubleshooting and structured analyses, as you suggest.

 

Hi Lugnut,

I've got to agree with you really since I've made an assumption based on non validated data (albeit with a health warning!)

Since as I understand it an MB trained dealer has failed to resolve this problem we must ASSUME that the problem needs CAREFUL consideration.....

We'll see how things pan out. I chose to respond to this problem because it looked interesting since MB dealership couldn't resolve.

........................................

BTW not being an MB guy I thought disconnecting the battery was likely to cause all sorts of issues with having to reset / relearn several systems. e.g. Roof, windows, radio code, security etc. Easy when you are familiar with the required procedure but a little scary if not, or maybe everything on this type of vehicle is now self learn?

Stuart

 

seems that the problem is as simple as too tight adjustment on the linkage to throttle or the throttle valve itself (wiring harness, connector, etc).

 

Yes, the things you listed will be necessary after reconnecting the battery. I wouldn't call them issues or scary per se. If you can't find the radio code then there may be an issue, but it's easily resolved by visiting a dealer with your VIN.

I'm just advocating the simplest approach first, then the complex, rather than the other way around.