My car is working perfect 9 months a year, but when outdoor temperature is +20 C or more, it easely goes into limp mode in stop and go situations. Sometimes after being parked for more than an hour, and the only cure is to open the hood and ventilate for five minutes and it works again!
There is no indication on the MB garage test tools, I have been there several times. One time I got there limping without turning ignition off, but as soon as they open the hood and connect the computer, everything is back to normal. When I leave, it starts to limp at the gate...
Limping in my case is the same feeling as when the speed limit comes on at 250 Km/h, but this reduces the revs to 1500, which is max 30 km/h on 2:nd gear.
I have not started to change pieces since I have no idea where to start, and the garage refuses to check the car with the hood closed, so they will never be able to detect the problem!
The car is a 94/06 and I have had this problem from about 20.000kms and now it is at 50.000km, pretty low mileage and well serviced all the way.
Anyone with similar problems and possible solutions are most welcome to reply. IŽll follow up on your ideas, so we all know for the future...

My first worry would be the wiring harness. Check the archives for the variety of problems this causes.

It sounds like your ASR or EA/CC/ISC systems are what would be involved. Codes should be checked and be sure linkages are free and adjusted properly. The type of limp home function that does what you describe is protecting against unintended acceleration (throttle taking off on its own).

Had a S500 this week that did this; turned the ASR light on and the Batt light. We caught it in the act on actual values for DI and the screen I was looking at (I was monitoring timing basically as it only was setting a shift overload code and the speed was limited but surging) had timing and a number of other values including battery voltage. The timing was pulsing between 17 and 35 degrees and I happened to notice that the batt voltage was swinging from 14v to 17.7v. We tried a regulator but it still was full fielded. An alternator solved the problem. Twenty years ago I would have disassembled it and fixed it. Now the time is too valuable. (The car belonged to a tech in another shop who was doing the labor)

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks for your reply. I have read a lot about wiring harness and bad contacts and tried to connect and disconnect and twist to find anything that could affect this mode, but so far nothing that gives me a clue.
My car has only ASD, not ASR, and no lamps are coming on or anything in the memory that can indicate what has occured. So I am leaving the alternator out of the picture for the time being.
The major problem is that just a few degrees lower temperature around the engine and the problem disappears again!?
What can be so sensitive and remaining coming back for the third summer?
It seems like a bad connection and I have read about the crank position sensor causing similar problems. Can it be so sensitive to surrounding temperatures as a couple of degrees? And if so, what to look for?

I have an S500, and in this case the computer modules are limited to 55șC.
If the temperature rises above this value the car goes into "limp mode".
There is a ventilator in the modules compartment that assures the temperature remains below 55șC in all conditions.
Check if your model has this vent. It could be it.

I hope it can help...

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Folgado
S 500

Thanks Folgado,

IŽll check for a vent, but are you talking about a mechanic/electric fan or just a open air inlet?
In my car the area is behind the battery on the right side behind some cardboard covers. Dont know if the temp can reach 55 there but otherwise it sounds promising since I have no other explanations.
L.

Have now checked for any "vents" around the computer units and found it very enclosed. I actually tighted the cover even more to at least shield for heat coming in...

Here are two other longshots; the problems started after a service where the battery was disconnected. At the same time they fixed the cruise control, that was not working at all, but now works from 40 to 110 km/h, over that it will not engage. Is this normal? The outside thermometer did go down from ordinary readings to exactly ten degrees lower. I suspected it to be something in connection with temperature shift during the time the battery was disconnected. A sort of accidental calibration. Is this possible and can it be calibrated at all? Can the thermometer misreading or the CC limitations affect my ECU to put the car into limp mode?

The MB garage guys just shake their heads but they seems to know absolutely nothing when they get no fault codes.

Fortunately (for me) the midsummer weather here in Scandinavia is cold and wet so the car is working just fine for a couple of days!

L.

I don't know what the "heat" has to do with it, but a faulty cruise control is the sign of a bad throttle actuator, which could be putting your car in limp mode.

The throttle actuators have potentiometers that wear out over time, but more likely in your case, the insulation on the wiring harness on the throttle actuator itself suffers from the same degradation problem as that of your engine wiring harness.

This is a systemic problem on all M104 engined cars from 1993-1995.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

OK, the wiring harness is still on the suspect list, but I can still not find out why it should work flawless nine months a year and struggle when a few degrees warmer?

Last nite I found a hint on a Norwegian MB-site where someone was asking about a little fan in the area to the right of the passengers feet? It should be running all the time and blowing the air upwards to the dash speaker area. They assumed it to be something for the climate control.

My question is if someone out there know if this might be the "missing fan" to cool the computer compartment behind the battery??

IŽll look for it later, but it should be good to know a little more before I start dismantling the car...

L.

Your engine wiring harness is still a suspect, but so is your throttle actuator.

The wiring harness that I referred to is the harness for the actuator. You cannot buy it separately. It is part of the throttle actuator.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Thanks for coming back on the actuator harness, but as far as I can see, all the wires, everywhere around the engine, looks just fine, like new.

I also tried to get in to where this fan was supposed to be, but it seems I can not get there without causing minor damage to the panels so IŽll wait until someone can confirm if this is a useful lead. CouldnŽt hear any fanlike sound from there though, meaning there is no fan or it does not work...

Another thread suggested the wiring harness issue is only on US spec cars, but I never saw any conclusion on that? Does anyone know?

Even if it drives you mad when the car goes into limp home mode, it happens only under certain conditions, otherwise everything is and works in perfect order. Starting to spend big $$ on replacing pieces without knowing the result is even more frustrating...but soon it is my only option!

As for the engine wiring harness, did you look at different areas of the harness? You can cut open the black fabric covering of the harness to inspect the condition of the insulation. The only place to inspect without cutting it open is at the injectors.

There is a 100% chance that your wiring harness is already bad, or is in the process of going bad. All wiring harnesses (at least in the U.S.) on all M104 engines are bad due to defective insulation from 1993-1995.

I don't know how you can ever rule it out as a source of your problem unless you replace it.

By not taking care of it now, you are only putting off the inevitable.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

IŽll talk to the MB-garage on monday, they have never ever mentioned bad harnesses here. It might be that it is already replaced during the cars first ownership, I have no details of that, only that the car was serviced every 2000 to 3000 km:s the first six years!
If it was a common problem, MB might have just done it without saying it?
Unfortunately the garage has a very "high profile", you are not even allowed to talk to the mechanics. Once they had my car hooked up to the Star diagnose machine, idling for 45 minutes and nothing happened. I tried to tell them the hood has to be closed, but they knew better. When I left I came 200 meters before the car got into limp mode again. What do you say.
With such guys it is easy to get ripped off, if I have no idea myself on what to do..., at least I have got some ideas here that I will propose and listen to what they might answer.
Still nobody that knows anything about that little fan as described above?
It should be a relief if it was so simple...

Still the same problem. Been twice to the MB service again and they say they have no idea whatsoever! Only cure is to start replacing pieces, trial and error, and they will charge me for all of it!
I have been "testing" almost every cable connection and vacuum hoose for bad functions but nothing. Again, all cables are like new!
Last week I made a 800 km trip in one go, hot weather and no problems. Got stuck in traffic and car went into limp mode. Opened the hood for a couple of minutes and the engine came back to life. Drove straight home again, yes 800 km without a hickup. Next day I was in stop and go traffic and the limp mode came back. Again vented some minutes and could then drive home again.
Now we have 30° celsius, and engine temp stays around 88-90 as normal,
but it is the ambient temp that causes the limp mode. And releases it.
Any new ideas are very much appreciated, since I would like to drive the car even in the summer. From September to May it never stalls...
L.