ASR malfunction

[cotovelo]

hi!

the ASR light of my 94 E320 wagon came on already twice when i was going 80mph with the cruise control on. it doesn't happen inmediately. it happens around 15 to 25 minutes after i set the cruise control. if i restart the engine and don't use the cruise control everything is fine. any ideas? i'd like to take it to my local mechanic but i'd like to sound a little bit familiar before i present myself. any ideas on what's going on? is it something a DIY person could fix? is it expensive to fix? etc.

thanks in advance,

carlos
cotovelo@yahoo.com

Hi Cotovelo, I started having problems with the ASR system back in November 2002, and after $ 2,200 in repair cost the problem is still persist. My problem started differently that yours, but from what I’ve been able to research the diagnosis of the ASR system is not as simple as other systems.

Use the search function and read other member’s problem relating to ASR. You can read my posting on this issue. Best of luck, and advise if you shop resolves the problem

[Arthur Dalton]

Check that tire inflation is the same and the tires are same size/make..

I have also seen ASR glitches from an bad OVP relay.

[tivoliman]

The dealer's computer found the problem quickly on my W140 (500SEL)

Fo me, it was a fuel system control unit.

We could not rationalize why the ASR light would come on with a fuel system problem, but it did.

Good Luck.

Suggetstion - use Mercedes computer to resolve - then take your own actions to fix.

[stevebfl]

I just had an interesting repair of an ASR problem on a 92 500SEL.

It probably doesn't apply here but it will go to the issue of why the engine management system is involved (along with quite a few others).

One of the interesting things about this repair was that the car owner was another shop owner/technicain. Because of this we worked the problem out together. The main symptom was that the ASR light would come on just after the tach dropped to zero.

A scan of systems found a code in the EA/CC/ISC module for no TN (engine speed signal) from the base module. The problem was intermittant so we started by breaking out the speed signal. We did it first at the instrument cluster and found that sure enough the TN was leaving when the tach left. We looked at the crank sensor signal but knew it had to be alright as the engine continued to run. We then looked at the TN signal from the ignition controller to the LH controller. We monitored the signal at the tach and from the ignition (should be the same) on two channels of my scope. When the event occured the signal at the tach left but the one from the ignition to LH continued.

We were then faced with breaking out the connection from the LH to the base module. Tough but we got it. The signal also maintained at this point. Here is where working on another techs car was a benefit as the problem was intermittant and often required monitoring for 20 minutes or more (I set up - he monitored). From the wiring diagram we then knew that the base module had to be the culprit (sort of what the fault code had said). A used base module did the trick.

The point here is that the ASR uses throttle control and timing control (along with brake control) to keep traction in control. All of the controllers are involved. A lack of CAN communications along with numerous other factors are possible faults that can set this off.

One thing that comes to mind is the throttle safety switch. This switch is located on the throttle linkage and is designed to monitor the continuity of contact between the throttle and the gas pedal. One can set this off by moving the throttle at the motor with the engine running. because the gas pedal didn't move the system recognizes the disconnect.

During cuise control, this activity has to happen (the disconnect of throttle to gas pedal). The circuit that is monitored is bridged by the cruise function. This might be a point to check on. (I am not sure how - but my first stop would be the on-board diagnostics).