ASR light on when cold

[Boudreaux]

Scroll down and look at the photos of this thread so that you can inspect your wiring harness to the injectors.

Engine Wiring Harness

[JimF]

ETA and you can do it if I can!

Check my page (click the 'www' icon below) for details; see the details in MENU#24.

The worst part is that #@&@% spring!

[speace]

Okay, it has been some time since I posted to this thread, but I have now declared my problems to be FIXED! FINALLY! Yea!

there were two significant items replaced and I don't know what really fixed what, but here is the analysis and I'm glad the problem is GONE!

The three long-term elusive problems with my 500SL were:

1) Missing a lick every 3 to 5 seconds while idling. This disappeared with the fixes below.

2) The engine would miss on seemingly one cylinder on initial accelleration from a stop. This miss would last 3 to 5 seconds and be gone. It would be there if I accellerated softly or fiercely. This was intermittent and would disappear if the car had not been driven for several days. The more I drove it each day, the worse it got. Again, if I let the car rest a few days it would be a while before the problem returned. My shop said they noticed that the number 8 cylinder was about 10% weaker than the others. The problem would go away for a few days if they "bled" the line form the fuel distributor to that injector. They did this bleeding exercise twice with the same result... They replaced the number 8 injector. ( I think it was just posessed...)

3) The ASR light was coming on intermittently and the car would go into "Limp Mode." This had nothing to do with being cold or hot. It would only happen while coasting. Coasting up to a light, coasting down a hill, anything where my foot was off the pedal... This happened about 2 to 3 times a day and was so bad that I learned how to put the car in neutral as I continued coasting and restarted the engine. I could do this and get my power back in about 4 seconds flat! On the 92 SL models the "ASR Codes" are reset when the car is restarted so I drove the car to the shop with the light on. The code pointed to the throttle motor and/or throttle position sensor. I considered replacing the throttle motor, (evidenced in the thread above) but learned that it had already been replaced in their first attempt to solve the problem a year earlier. They had gone in to replace the idle switches?? and had to replace the throttle motor. Many of you had suggested that my wiring harness was to blame. My 92 400E had a bad engine wiring harness and suffered similarly, but this harness was inspected and appeared to be fine. My shop replaced the "Throttle Position Sensor" on the firewall and this has cured the problems! This sensor is connected to the accellerator pedal and sends the pedal movement information to the computer and it controls the throttle motor accordingly to open the throttle body.

Thanks to everyone for using up valuable brain cells on this one, and I wanted to share the results. Perhaps this will help someone else with their similar woes...

[LeaUK]

Great stuff - I've been reading up as much as I can about this problem as I like to be prepared - and guess what, my ASR light came on too last week or so, therefore I'm glad you posted your results here for all to see.

Unfortunately on my 92 there is limited fault codes none of which help!

Any idea on part cost for the offending sensor?

Cheers
Lea

[speace]

Lea,

Yes, it was pricy... $535.00 us dollars of course! My shop said they don't like to replace the throttle motor without replacing this "Throttle Position Sensor." I see it listed on my receipt as an "Accellerator Potentiometer." They said that this sensor can cause the Throttle Motor to burn out...

They said that the ASR codes on my model were limited too, but they also said that each time I turned the car off the codes were being reset. that is why I took the car to them still running and with the light still on. That is when they finally narrowed it down.

I know a good bit about electronics and the potentiometer failure makes a lot of sense. I did not keep or inspect my bad part, but potentiometers are essentially a brush or wiper that mechanically slides along a carbon strip or a coil of resistive wire. The wiper gets dirty and makes a poor connection or static. Have you ever had a radio or TV with static in the volume control? It's the same principle. This static would confuse the computer and cause it to shut down and turn on the ASR light.

[LeaUK]

speace

Hi - fellow Electronics person ;-)

I'm an Electronics Eng by trade and I did enjoy you very nice potentiometer explanation

Just to clarify, was the $535 for the accelerator pot alone or for both the throttle motor and pot? Reading your post again I guess it was for just the pot as you mentioned that the throttle motor had been replaced previously?

Damn that's expensive! I'm surprised you didn't keep the old one - I would have loved to have identified the failure mode.


JimF

Hi Jim

I have read your site from top to bottom but unfortunately your electronics are way more advanced than mine - so I guess the US had different legal requirements of that age. My '92 has only very minor fault code diagnostics all accessed via a 9 pin connector under the hood around half way down the car - a real shame but there you go!

I spoke to a rep the other day who sells diagnostic readers and he mentioned that models '92-'94 were a real pain as MB mixed and matched the systems something chronic!! You can never tell what system is within until you lift the bonnet. Of course, as soon as the SL was fitted with ODB (I think around '95) then it all became much easier.

Cheers
Lea

[JimF]

Learoy, your picture shows a '93 500SL but you said '92'?

The electronics in the '93 should be almost the same as my '94 and they are mixed; some analog and some digital.

The '93 uses the 119.972 LH engine whereas the '92 uses 119.960 KE. So I guess that your pic is wrong, since if it was a '93, it would be "SL500" instead of "500SL"!

But for the '93s, the DTCs should be the same as shown on my page(s).

[LeaUK]

Hi Jim

Let me first say what a great resource your web page is, and the amount of work that your car must have taken - wow 'you are the MAN'. Thanks.

You are quite right, the text above my picture shows '93 and indeed my car was registered '93, but it rolled off the manufacturing line on the 11th December '92 - so sometimes I refer to her as a '92 for clarity. Sorry if that confused anyone!

Mine is indeed a .972 LH and was built in '92 and has NO CAT. In in the UK, law insisted on CATs in '93 so I guess that MB introduced the .972 earlier without CAT. Also she unfortunately doesn't have the advanced diag ports ie the 16/38pin connector, only the 9 - when it comes to diagnostics mine is way behind the 94/95 cars which is a real shame.

I suspect MB introduced a rolling badge change here in '93 or '94, others on here I know can confirm but remember that the US is completely different to euro. You guys had CATs way before us and I believe also insisted on advanced diag - which thinking about it probably naturally evolved from your cars having CATs!

The 92-94 period of the 129 is very frustrating over here as MB seemed to really mix and match their systems. Sometimes the only way to confirm is under the hood!


Cheers
Lea

[LeaUK]

Sorry if I've manoeuvred this thread a little off topic!

Jim

I have been puzzled for several months now re the diagnostics on these cars and have asked several deemed 'knowledgeable' specialists about diags and connectors (MB dealers etc) but many said that the mine was only fitted with the 9pin - but today I am over the moon.

Yes indeed, you are quite correct, and this is great news. It was my original belief that the 129 was fitted originally with the 9pin then 16 followed by the 38 - and maybe an additional ODBI/II at latter stages. But I stand corrected.

I've recently joined http://www.alldatadiy.com/ (excellent resource for schematics etc, the best I can find) and after reviewing your web page, Alldatadiy and my own gut feeling I re-investigated. Bearing in mind UK cars are right hand drive I looked up the F23 box (it's obviously on the opposite side). For some unknown reason I thought this was some kind of hydraulic reservoir and never thought anymore - how wrong can a guy be!

Indeed the 38pin DTC connector lives under that black cap - a simple twist and all was revealed - the 16pin connector was fitted to the 119.960 (CIS) engine. I then stripped the F23 lid away and took some piccies - just in case.

Great news - now I maybe able to diagnose that annoying intermittent IRCL problem as I have a DTC scanner ready and waiting ;-)


BTW - when you say Analogue do you mean pulse codes or analogue in the real sense, ie., a linear voltage representing an error?


Cheers for making me think again

Lea

[JimF]

into it further! It had to be that way otherwise the euro version would be completely different.

Anyway, with a scanner and the 38pin diag connector, you can have a 'ball'!

Let us know what you find.

[Tanman]

My 92 Sl has been in at the dealer's for a week now and they still can't figure out why the ASR comes on when the engine is cold. Mine recently came on for the first time ever and only comes on when the engine is cold (within 5-10 mins of start up). When it does, I stop and restart and it goes away. ASR does not come on when engine has warmed up.

Have asked the MB service guys to check the wiring harness but they say they have and it is ok.

Any ideas?

[LeaUK]

Boy I hate these damn ASR issues! I managed to cure mine and it was very similar to Speace's symptoms, take a look here but yours has different symptoms! Still, I would check the accelerator cable setup first.

Lea

[Tanman]

Thanks Learoy, your post on the accelerator cable was actually the first thing I handed over to the benz guys 2 weeks ago when this problem first started. They said that it was fine...might get them to look at it again. The MB service agent has just told me that he has had 5 of his guys working on trying to trace the root cause of the ASR peoblem for the last week but still no joy.

Am getting really frustrated with the toy...not much fun when your toy starts to play up and no one seems to be able to fix it.
Will keep plugging away at it...

[speace]

I will add something that my shop had me to do to help them disgnose my innermittent ASR problem. They said that my system (1992 500SL) did not retain the codes and that by restarting the engine I was clearing the clues. At their request, I 'limped' the car in while the light was still on, left the engine running, and let them test it immediately. I did not leave it with them that day, but they fixed it on the very next attempt by replacing the throttle position sensor.

My problem was not particularly cold sensitive so, it might not be an exact match for your problem.

Good Luck!

[Tanman]

Thanks for the input Speace. The shop has had my car for over a week now and everyday, just when they think they have fixed it, the ASR light starts up again. They say that everytime the ASR light comes on, a new and different fault code registers.