I have a 1995 S420 which goes into limp mode when I hit the accelerator. I took the car to an
independant Mercedes dealer who changed the brake light switch this did not cure the fault he said
he thought it was the ASR module but could help no further. Before I go down the road of changing the ASR conrol could anybody help please.

 

First of all Limp mode only kicks in when there is a transmission problem. IMHO I doubt it is the ASR. If you want to save money in the long run I would go to a Mercedes dealer who have the proper equipment to find out what is going on with the tranny. I checked my owners manual and it specifically says if the car goes into limp mode there is a malfunction in the transmission. The condition may be accompanied by a Check Enginer light. In limp home mode the tranny will only shift to 2nd gear or reverse gear can be activited.. To engage 2nd or reverse, stop the car, move the selectot to P or Park turn off the engine wait 10 seconds then turn on the engine and move the lever to D or Drive positon, for 2nd gear or R for reverse. HAVE YOU CAR CHECKED BY AN AUTHORIZED MERCEDES BENZ DEALER ASAP. I have both ASR and ESP and BAS and if they malfunction these systems cut power to the engine, nothing is mentioned about limp home coming on with ASR. It is a transmission problem

 

That is a FALSE statement. There are several things that initiate the limp home mode, including ASR problems.

Have you had the wheels removed recently? Has the car been on a dyno recently? Is a rear tire flat or nearly flat?

Try switching the ASR off and check if it still does it. All models don't have this feature so you may not be able to disable it.

 

If your car is going into limp mode when you accelerate then i almost bet you its your Accelerator pedal sensor. I had one the other day with the same problem. I replaced the gas pedal, cleared the codes and the car never came back into the shop.

 

Good information from both Lugnut and MBZtech. In my owners manual limp mode is descriped as a transmission malfunction. ASR, BAS and ESP is malfunctioning, the owners manual states only a loss of engine power. Always learning new stuff everyday.

 

Thanks for your time and information guys.
To Lugnut, MBZ Tech and wizard.

MBZ Tech suggestion about the accelerator pedal sensor seems a good bet.

I found this website you may know it had an article about ASR and its frustrations.


http://www.asashop.org/autoinc/july2005/techtips.cfm


Thanks once again will write when its fixed or If I am still puzzeled.

 

To MBZ Tech thanks for the advise you were right on track.
I took the car to my MBZ dealer mentioned your experience with this fault but they put diagnostic gear on the car and the codes suggested two
possible faults.

1 The wheel sensors on the front wheels These were checked and found ok.

2 The EFP module Part replaced still in fault

Further codes pointed to gas pedal and the sensor switch this checked out ok
Fault eventually traced to internal break on wiring on gas pedal.

Original EFP module refitted and wiring repaired.

Many Thanks

 

I love it when Im right!! Congrads on the repair!!