P0170 on 2003 C230 1.8 Kompressor
 

Driving down the road, no symptoms, nothing wrong. The Check Engine light comes on. I take it to a local parts store and they read out code P0170. A local shop wants $100 just for a diagnostic, I haven't even asked the dealer yet.

The car runs fine, but I'm due for the state inspection this month and I can't pass with that light on.

Any likely causes for a "fuel trim" fault without any driveability problems?

David Bunin

This is a good opportunity to learn about the powerful search feature of this site. If you search on that error, you will only find about 1,000,000 threads listing the cause (that is an estimate). It is the AMM. Aka MAF. Get a new one. Put it in. Problem solved.

You can replace the MAF with new one, or go to NAPA and purchase some MAF cleaner and try it. I had the same problem on my '01 SLK230 a couple of years ago and cleaning it worked. No more CEL. Next time I might have to purchase a new MAF.

And yes....let the search feature be your friend.

You can search on the cleaner also. You will find (almost) everyone found it an exercise in futility (worked for a couple of hours or less). But you could try it if you have 7 bucks and you feel lucky.

There is also a Service Campaign for replacement of broken cankcase vacuum lines.

A broken vacuum line can & will cause fuel trim issues.

I go with Doc on this one. The cleaning of the air mass doesn't seem all that good an idea. I know the contacts at the plug for the air mass used to corrode and cleaning then and applying an electrical contact cement from VW would solve most issues. I believe if you do a r/r of the air mass the process removes contaminant from the plug.
Bill

I should have mentioned that I did use the search function and I did find a million posts for that code, but I had two problems. First was just general information overload and it seemed like anything and everything was suggested as a fix. The second was that it seemed like all of the posts listed the code associated with a driveability problem, and not the lack of any other symptom.

Our car has had the crankcase vacuum lines replaced already in accordance with the Service Campaign.

Where is the mass flow sensor located under the hood? I could spray the connector (not the sensor) with some contact cleaner. How much should I expect to pay for a replacement sensor? Is it something that I can replace using standard hand tools?

Air Mass
 

It's in the air intake tract, it's a tubular device with a flat electrical connector attached. Replacing it is simple and straight forward, two clamps. Do a google images search and you will see what it looks like. If you remove it note the arrow indicating air flow direction.
Bill

AMM will be about $450 from the dealer or about $250 from this site. I bought mine from here, to support the site. Don't bother with the cheap ($100 or less) ones on eBay, they are new and good quality, but are typically the wrong Bosch part number and will make your car behave weirdly (trust me, I tried it). You can get the correct one from eBay for $250, but why not support this site?

I found pictures of the item online but I don't see where such a device could fit in my engine compartment. I am attaching a picture of my engine compartment. The intake (and the compressor) is on the driver's side of the engine.

Where's Waldo?

Check your PM's. Go to the link, see post #3 and click on the pdf file for the instructions.

The mass air flow sensor is mounted in line behind the air filter box, it has a square electrical housing on the top . The harness connects at the top side of it. The removal requires a special clamp removal tool to release the clamps that hold it in place.

Thank you very much.

When I looked to buy the part, I saw that it was not the "tube like thing" that I saw when I did the Google image search. It is much flatter than that and I remembered seeing it from work I did previously.

Mercedes was nice enough to put the electrical connector right on top, so I've cleaned that now (without any other disassembly) but the Check Engine light is still on. If a dirty connector was the problem, how long before the light goes out?

The linked information indicates that the more common prolbem is oil in the harness going to the O2 sensor. I replaced my O2 sensor not too long ago, and I do remember there being some wetness in the connectors. Perhaps I should get back under there and spray some contact cleaner on that plug?

For that code it may need to be erased with a scanner.
Bill

I searched this site and only found the part for $450. I'd like to support this site, I believe you guys are a big help. Can you link me to the $250 part?

In the meanwhile, I am going to try cleaning the AMM/MAF. Seems like a no-lose procedure. If it doesn't work, I'll be no worse off than I am today.

If I erase the code with a scanner, I presume I'll have to drive some number of miles still before I can go for my vehicle inspection?

David