w140 ASR woes (sorry!)
 

Today for the very first time I experienced the dreaded ASR light and going into limp-home mode where the car becomes, literally, a powerless slug. I eventually realized after actually limping home 7 miles at 15 mph, that all it took was a restart of the engine and everything was fine. I went back out and drove around close to home to check it out and all was well for about 5-6 miles and it did it again after accelerating from a stop (the first time was decelerating TO a stop). I can't possibly see any connection, but I changed the oil and filter immediately before this occured today.

Okay, I have read through all of the posts (well, most) regarding ASR, limp-home problems from a search, and what I got out of them was that there is nothing definitive that causes it, and in fact could be one of 15 or 20, some being extremely expensive. My questions are these:
If I understand correctly, ASR is an anti-slip (traction) mechanism. Why then do things like brake light switches, neutral safety switches and throttle switches have any bearing on it? and why does the car lose 90% of it's power? and what connection does the tire chain switch have to it (is it a type of override)? Secondly, what is the first logical step to take? Thirdly, is the computer diagnosing strictly a MB dealer function? If so, from what I'm reading, that is not all that reliable anyway.

Help from anyone is appreciated, but particularly someone with a '92 500SEL :confused:

I'm far from an expert on the intricacies of MB ASR systems but as near as I can piece together from my reading and my own ASR problems, I believe the ASR and cruise functions are integrated in many models (like yours and mine) into an electronic accelerator module. If you look at it that way, it makes sense that the system needs to know if you're hitting the brakes, say. The system is designed so that if it senses any illogical inputs, it goes into limp-home mode.

When all is working correctly, accelerator pedal input is translated electrically (not through a direct mechanical connection) into changes in the opening of the throttle plate. The reason for this is so that the ASR system can instantly disconnect that same input, if, for example, you have the accelerator floored while your wheels are on an icy patch. I believe the limp-home mode basically allows a mechanical override if the electrical communication between accelerator and throttle is lost due to malfunction.

In terms of practical advice: NO, you absolutely do not necessarily need to go to an MB dealer. You do need to have the codes pulled, or even do it yourself. The codes will lead you or a tech to the right diagnosis. In my particular case, an independent tech with the appropriate software diagnosed my bad brake pedal switch and cured the problem.

I think an ASR problem is almost always caused by a bad throttle actuator.

<<and it did it again after accelerating from a stop (the first time was decelerating TO a stop).>>>

Classic Stop Lamp Switch...

Here is another point to ponder: Do you think that the ol' computer got some bad information from whatever source (static, rfi, emi, etc), and thought something was wrong with one of the ASR inputs? Here's why I ask. Over the past month or so I have been noticing weird, unrelated failures with things that were working fine previously: The vacuum self-closers on the doors and trunk, 4 of the 13 speakers, the ir locking/unlocking, and drivers seat memory, to name four, and now the mysterious ASR problem out of the blue. Also, the car had not been started for about 2 weeks prior to yesterday. I got the bright idea to simply "reboot" the car last evening like it was a 2 1/2 ton computer. I disconnected the battery for like a half hour to give any capacitors time to discharge, then reconnected, did the radio code and damned if now everything I had mentioned above was suddenly just fine. I took it for a 25 mile test drive today with stop and go and 70mph driving and no ASR light! I know it's way too early to tell, but I'm going to drive it all week and see what happens...I'll post the result, good or bad! Wish me luck. :D

Well, it has been over a week now and the car has been driven every day (a total of 150 miles give or take) in all conditions and ALL systems are functioning just fine and not a hint of an ASR light. Considering that prior to "reboot" the ASR was rearing it's ugly head every 4-6 miles, something has to to be made of this. Does this mean that reboot is a cure for all ASR problems, most definetly no....but I would sure consider it as a "first try" if you get one out of the blue.....particularlary if you are experiencing other electronically-controlled system failures for no reason. My fingers are still crossed, but I'm thinking with every passing day (of no ASR tbls) that there was no problem other than what engineers call "unexpected results" from whatever sensor input that caused it for whatever reason....now that sounds scientific for sure! :)

maybe low voltage
 

when a lot of electical or electronic items start not working properly low volage sometime can be to blame. you stated that the car hadn't been driven in 2 weeks prior. You may have "a slow to react" voltage regulator in your alternator not charging the battery up fast enough. By driving it this week you have charged the battery back up. the "power on master reset" reboot ( I am an old electronics/main frame guy)" just cleared all the rubish, stuck registers, etc. and reset everthing.

just a thought and good luck!

Steve
1992 W140 300SD

Well, just an update. It's been over a month now and I haven't had a reccurance of the ASR problem since "rebooting". I am definitely leaning towards a power problem and for this reason: I am doing a full Leatherique restoration front and rear and had all the doors open (and the resulting courtesy lights were on) for a lot of hours over the 4th holiday, as well as the radio for entertainment. Afterwards I noticed the door closures weren't working again as well as various speakers. I rebooted again and all is well with those functions. I strongly suggest to anyone experiencing a very intermittant (or first) ASR problem to try this. I know it isn't technical or "in the books", but it sure works for me.....and a lot cheaper than throwing parts at a problem that you don't know a real reason for. A consistant ASR problem is a different thing altogether.

ASR
 

I also have a 92 and have had "limp home mode" twice during the last year. I turned it off and restarted, the "mode is a real slug. I was told to change the brake light switch before doing anything else. I will do so the next time it acts up consitently. All the comments make sense, there are many items involved.

ASR issues
 

Talk to the good techs at the dealers and Indy shops--the wiring harnesses are crap and the individual wire insulation inside the black sheath turns to powder (bio-degradable).

Low voltage scrambles a lot of things and is the first fix required.

Then pray a lot, don't TOUCH the harnesses, much less flex them--or be prepared for lots of glitches until finally you replace the things out of desperation. Sobbering to think of 2-4 harnesses @$500-1000 each, plus 4-20 hrs each to replace them. +electronic throttle actuators (2 on the 12 cyl engines@ $2500 each)

I inquired about why NTHSA has not ordered a recall. Seems they have not heard about any accidents caused by this--the engine does not stop==it just goes into limp in mode and 'allows you to pull out of traffinc safely.' Wonder who MBZ took out to the bars and whereever to get that friendly analysis.