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Matt, Engineer
Category: Mercedes
Satisfied Customers: 21864
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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95 S420: the ASR module and the light came..throttle..light went

Resolved Question:

My ASR light keeps coming on I replaced the ASR module and the light came on again could it be the throttle acculater 95 S420, as i said before when the ASR light came on again I replaced the new one with the old one and the ASR light went off, what could be the problem
Submitted: 6 years ago.
Category: Mercedes
Expert:  Matt replied 6 years ago.

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

However with ABS / ASR systems 99% of the time its a problem with one of the wheel speed sensors and I'd first check the connections at all four corners first for any signs of corrosion or chafed wiring.
The sensor is located in the wheel hub so you'll have to remove each wheel in turn to inspect them all.
Also check that the toothed wheel that the sensor points to is clean and free of any debris.
you can check each sensor's function by plugging the two output wires into an AC voltmeter and spinning the wheel quite quickly, you should get a voltage signal that increases with rev's.

It could be that the fault is only a bad connection to one of the wheel sensors.
This may be remedied by removing each wheel in turn and unplugging each sensor and cleaning the contacts with a squirt of electrical contact cleaner. Then refitting.

Customer: replied 6 years ago.
When my ASR light comes on the transmission does not shift properly the car idles up, and the gas pedal has to be pushed way down to get any kind of connection. There is alot of play in my gas pedal when the light comes on, how can it be a sensor in the wheel.
Expert:  Matt replied 6 years ago.

ASR = Anti skid regulation ie. traction control

the system uses inputs from the wheel speed sensors and engine and gear selection to rein back engine power if it thinks the wheels are spinning it does this by closing the throttle so it would feel that the upper reaches of the throttle suddenly aren't doing much

so if you have a faulty or bad signal from a wheel speed sensor the ASR controller can be fooled into thinking there's wheelspin and so cut engine power/ throttle accordingly
Customer: replied 6 years ago.
The ASR light came on about a year and a half ago, and I had a diagnostics run on it, and even though the ASR light was on the diagnostics test came back as a throttle accuator I replace the throttle accuator and the light went off this was not a new part it was a used part a year and a half ago and the light has come back on so are you still convinced its a wheel sensor? And should I have the dealership check the wheel sensor or is it a number of things not just one thing do I have to replace all those parts cause even the diagnostics from the Benz dealership did not mention anything about a wheel sensor the diagnostic came back ASR module.
Expert:  Matt replied 6 years ago.

this is the 1st time you've mentioned that you've had a diagnostic already run, was this done recently?
Customer: replied 6 years ago.
I had the diagnostics taken two weeks ago it said it was the ASR module. While I am waiting for a response from you I went outside and started the car and the ASR light came back on, cut it off turned the ignition on three consecutive times without starting the vehicle and on the fourth time I started the vehicle and the ASR light went back off.
Expert:  Matt replied 6 years ago.

I'd suggest checking the connection to the ASR module itself as this could be a poor electrical connection

the abs and asr module is one part and is located under the hood, behind the drivers front light. there is written ABS,BAS,ASR.

if you unplug the module and spray the contacts with switch cleaner that should help and inspect the wiriing for any damage especially where it passes over other components
Customer: replied 6 years ago.
Tis is a 95 s420 and the box that these panels fit in is on the passenger side right front up by the windshield I'll try to spray the plug where The ASR goes in or should I take all the modules out, there are five in that box should I spray them all or just the ASR? And is there another connection place behind the drivers side front light?
Expert:  Matt replied 6 years ago.

I'd suggest to do a thorough job - 1st disconnect the battery ( ensure the keys are outside the vehicle as it may lock once the battery is re-connected)

then unplug each moduel box in turn and spray the contacts on both the box and the connector block

then replace all modules and re-connect the battery
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