The check engine light on my 2001 SLK has illuminated five times in the past 3 months. Each time it is taken in for service, the computer diagnoses the same problem, and the dealer installs the same new part. I drive the car for approx. 5-10 miles and the light bings on again. During the most recent visit, a complete top-to-bottom diagnostic was performed and several parts were replaced. In addition, the car was driven for 120 miles before it was returned to me. I drove the car for approximately 30 miles and the light came on again.

Does anyone know the source of the problem (I've tried the simple "fixes" like getting a new gas cap)? Also, are others experiencing this problem and, if so, what are you doing about it?

 

How ridiculous. One trip to the right service tech should have found your problem. When MY CEL had the same symptoms, it turned out to be the MAF sensor. Has anyone checked your air filters to see if they are plugged up. How are your spark plugs? and boots? Fuel pressure? fuel filter age? What codes are you (they) getting? Hold on to your wallet before letting those bozos sell you more stuff you don't need. Post what was found and I am sure someone here can help.

 

Hi,
The computer doesn't tell the technician what to fix. Just why the Check Engine Light (CEL) came on.
In order to help you I need more information.
Mileage, What have they changed. What was the code. and even more important What are you doing when the light comes on. Accelerating, Starting off etc. in as much detail as possible. The computer also states exactly what the engine was doing when the CEL came on if the technician uses his scan tool correctly.
Does this guy know what he is doing?
Stuart

 

Hi again,
I agree with BikerDrew that it will most probably turn out to be the MAF Mass Air Flow Sensor. These are quite expensive so you don't want to change it unnecessarily.
The key clue to a MAF going bad is a P0170 code or similar coupled with a high LTFT value. this is why it is so important to have the information given by "the computer".
Since you have no doubt paid heavily to get to where you are this information should be made available to you. It the first step in any diagnosis of a modern car.
Do you drive spiritedly? (i.e. Use full throttle / high revs quite often). I don't understand why the garage thought all was OK and the moment you drive the car there is a problem. High revs / full power combined with a dirty / defective MAF gives an intermittent problem which only shows up when driven spiritedly.

In case you are confused by my statement that the on board computer doesn't tell you what is wrong. The computer states for instance MISFIRE on BANK !. It doesn't tell you what causes the Misfire, That's down to the technician.
Stuart

 

Here is all the information I have regarding the car and the circumstances under which the check engine light comes on. The car is a 2001 SLK 230 sport with a manual transmission. 22,100 miles. The compter code that registers is P0170 (it is always the same code). The Mass Air Flow sensor has been changed three times. The light usually comes on when I am stopped at a stop light, but it did come on once when I was driving (at about 35 mph on a city street). The car gets driven spiritedly only periodically. I do not know if the problem has been resolved yet. It has been at the dealer's service center for over two weeks while they wait for a part from Germany (unfortunately, I didn't get the name of the part). Apparently, it is uniquely encoded for each car, so it cannot be stocked.

To date, I've been lucky- the car is still under the original mfg warranty, and I have not paid one red cent for any of the testing and "repairs." Any help/information regarding the problem would be appreciated.

 

Hi,
OK we now have some additional information.

The MAF has been changed 3 times! WHY?
The MAF WAS certainly a key suspect but recognising its cost I would have ensured it was at fault by doing some tests before changing it.
What possible reason can the garage have for changing it so many times. I make the assumption that they fitted NEW BOSCH MAF and not some secondhand / remanufacturered etc lookalike.
The key bit of missing data is the Long Term Fuel Trim (LTFT). If these are high then the fuelling system is suspect. MAF is just one part of the system.

Also need to know what conditions were prevailing when the Check Engine Light CEL was illuminated.
Reading this information takes about 10 secs once the computer lead has been plugged into the car.
Without this info we are shooting in the dark. Resetting / Changing the ECU will loose this valuable data.

Is this an MB dealer we are talking about? They SHOULD know better than us what is going on.

Looks like they have decided to change the main engine ECU (computer). My view is that although this could be the cause it is unlikely that the ECU would go bad at 21,000 / 5 years in normal srvice

They're paying!!

Keep us posted.

Stuart

 

any update on this so far. i'm having the same problem. CEL on, it only happens at stop light when engine is idling. Sometime CEL turns off by itself then turns on again after about 20-50 miles.