C36 Check engine code?

[Rocky]

I recently had my check engine light go on for a few days then off for a few. On and then off. Got an OBDII reading. Code was P-0170, something about a fuel trim malfunction.

I brought it back to the dealership and they said I need a new air mass sensor. IS this true? AMS is expensive. Only got 100,000KM on the car.

[Gilly]

Yes, this is fairly common, and not just on Mercedes either. The MB description is "self-adaptation at partial load at limits", I believe the description you listed is the generic OBD II description. The fuel trim is a shift in the operating limits of Lambda control. It takes several things into account, one of the important things is the air mass being sucked in by the engine. If the mass air flow sensor is incorrect, the fuel trim will reach a point where it says "Whoa, I can't compensate for this amount of air any more!" and will be unable to shift any longer without really having a whacked out mixture. It's really up to the technician to decide why this has taken place, there are several other reasons, but the air mass sensor is definitely the cause du jour for this code. How many dozen times do you need to see this code and have it be because of a bad mass air flow sensor before the technician can simply see the code and recommend an air flow sensor???Gilly

[Rocky]

Thanks for the reply.

I read back a see that alot of M104 engines have this problem. Was there a recall or anything. My car is out of warrantee and wonder if MB wil cover it if they know it's a problem?

As well..I have a drop in K&N filter. Can this cause the problem too?

[Gilly]

They say to be careful to watch for any way that dirt particles can enter the fresh air stream from the filter, as sand particles particularly can damage the hot film matrix that determines mass air flow. As I said, all mfrs suffer from this, just not a perfect science yet I guess, hard to get them to last 100% of the time.
If you have a good relationship with the dealer, you can ask if they can help pay for this out of warranty, wouldn't hurt to ask.
Gilly
ps you can install it yourself at any rate, easy to replace it.
I like to reset the self-adaptation after replacement, but not crucial that this gets done, it will fall back into range fairly quick.

[Rocky]

Thanks again Gilly,

I was gonna maybe buy a refurbished one like on fastlane but they don't ship outside of the US.

That's kinda stupid to put unproven parts in a car like this is it not? Anyways we can just "clean" the hot film matrix?

[Rocky]

P.S. hehe sorrie.

Is the Air Mass Meter the same part # for all M104 engines?

[engatwork]

I like that

That's kinda stupid to put unproven parts in a car like this is it not?

I don't think it is the first time. How bout that biodegradeble insulation wire? I guess it is good for the environment

[Gilly]

On the wire insulation, the story I heard from what I feel is a reputable source, is that the insulation was supposed to be "bad tasting" to rodents and such. Evidently there is more of a rodent problem somewhere in the world than it usually is here in the US, and they were trying to cure this wire-chewing problem by using a foul tasting insulation. That's what I heard anyways.
I am not 100% certain that all 104 engine MAF sensors are identical. I know that on the new V6's and V8's, although they look identical, they aren't the same part. I would venture to guess that a C280 (104) is different than a E320 (104), although the E320 and S320 may be the same. Using that theory, your C36 probably has a unique MAF sensor. I am not aware that the MAF's were available reman.
The hot film matrix is damaged by sand particles, cleaning I don't believe is an option here.
I don't believe there is an economical alternative to what is being used at this time for MAF sensing. There were other ways to determine airflow, but not mass airflow, this is different than just "airflow". I always got a kick out of the first system like this, it was essentially the same but used a "hot wire" type sensor and was called LH-SFI, the "LH" standing for Luft-Hotwire. What you have here is HFM-SFI, which stands for Hot Film Management, the SFI of course is Sequential Fuel Injection. The current ME-SFI is still using the same MAF sensor, the main difference between HFM-SFI and ME is that the ignition system is incorporated into the ME control unit, on HFM and prior is was seperate of the injection control.
Gilly

[blackmercedes]

A Porsche buddy has a 928 and replaces his $1100 MAS as a maintenance item it breaks so often.

I understand the high-failure MAS are on the M104/M112/M113 models, with lower failure rates on other models, but still there.

BTW, yes, lots of car makes have this problem. But, the one our Mazda lasted 220K...

Rocky, I just had my '97 C230 diagnosed last week and it came up with the same problem. My independent tech advised me to try some fuel additive before going to the next step of replacing the AMF sensor. Did that, my engine light was reset and all appeared fine for a 3 days until it came on again. Guess I gotta go to the next step.

I see that you're in TO, what price were you quoted for the sensor? I was told it would be between $250-300 Canadian.

thanks and good luck.

[Rocky]

Wow that cheap? Can you tell me where I can get one for that price?

Only quote i got was from the dealer...about $700 bucks.

Sorry about the quote, it's actually $575. from an independent garage. I know that the dealership's list is around $700.

BTW, I had the car in the shop just yesterday and the scanner didn't pick up any codes. The car's playing trick on me as well as the shop. Rocky also reported that his CE light will go out on its own. So how do we test this gremlin??? The owner of the shop suggested that they would drop the new sensor into the car so that I could drive it around for the next week or so. If the check engine light stays out, its the sensor. If it comes back, the original sensor may be ok and will be reinstalled. Anyhow, the most impressive thing about this is the honesty and trust displayed by the shop owner. I'm driving around with his brand new sensor as well as a belt tensioner shock (that really did need replacing) and he told me to stop in next week to see what's up. If all is fine, he said that I could pay for everthing then. If not, I get the old sensor back, pay for the shock only, and we keep looking for the cause of the check engine light.

BTW, the shop is Young Stree Garage located in Ottawa Canada. Highly recommend!

[stevebfl]

There is an engine number break. The early unit is much cheaper and appears to be available rebuilt from MB for around $258. The later version doesn't appear to be available rebuilt and has an MB list price of 482. It is available through Bosch and fastlane probably has it much cheaper based upon my price. The two numbers are 000 094 05 48-88 (-88 for rebuilt) and 000 094 10 48.

stevebfl,

Thanks for the information, but if this is in US$, the Can$ price I was quoted is a pretty good deal.

Take care.

[ke6dcj]

You really need to have this properly diagnosed in a very methodological manner.

Just getting codes and throwing parts at it is very costly and unproductive.

We were getting similar problems and traced it to an intermittant O2 sensor connector.

Also, my tech uses an electronic cleaner that flashes quickly and is safe for sensors, to clean the MAS sensor.

A good read on how other system faults can cause a fault code is here:

http://www.peachparts.com/Wikka/EngineControls

A good OBDII scanner should be able to read the "freeze frame" data which tells you things like engine speed; temperature; etc., when the fault happenned.

It should be repeatable, so reset, and borrow the OBDII scanner and drive around until you get the check engine light.

Good luck,

:-) neil
1988 360TE AMG (w/1995 C36 engine, tranny, computers)
1993 500E