On my 1997, C230, the infamous "Check Engine" light came on and my OBD II checker is giving me a P170 Fuel Trim Malfunction Bank 1 Code.

Do any of you Einstein's out there what that translates to and how to fix the problem - Thanks

Read the live data for adaptation is should not lower then 0.68 or higher then 1.32 idle if you don't have vacuum leak or fuel pressure is ok no leaks , the air mass sensor should be your problem

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MB STARS Master Guild Technician,17 years MB tech
14 years independent shop owner

MB Stars, the adaptation numbers you mention are for partial load. The idle adaptation numbers are -1.000/+1.000 with .000 being the re-set value. I agree with your diagnosis though.

And the way to tell is to clear the old adaptation values install a test AMM and get the engine to 180deg and drive it a block or two. If it relearns to the same adaptation values then the problem is elsewhere. Most of the time the thing will relearn to 1.03 or .98 or some such and the fix is proven.

If the idle adaptation is the one out of limits and the lower partial is well within then this can indicate idle leaks. Had one just last week with the vacuum line off the airpump circuit had both codes. Air pump implausible and adaptation at limit. The limit was just at idle and the vacuum line was off at the manifold.

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

Hello all MB experts- I had the fuel trim malfunction code on my 95 C280 and I purchased a new MAF (from ******** in AZ) and installed it and cleared the codes by taking the battery cable off. The light stayed off for one whole day and came on the second day. I had it checked at AZ and I got the dreaded fuel trim malfunction- bank 1 message. The car had a lot more zip after I put the new MAF sensor on. Is it possible for the new MAF to go bad in one day ? I have read a lot about gas cap leaks- could this be the problem? I have no other codes showing. Should I reset it again by taking the cable off or should I have AZ reset it with their reader?
Thanks for your insight.

Larry

Hi All,

I finally took the Benz back to my local garage wher I spent a hundred dollars getting the diagnosis of a bad MAF last tiime. After I put the new MAF on and reset the CEL, it came back on the next day. Well, I didn't want to admit to my wife or anyone else that I just wasted $280, so I kind of ignored the light until today when I took the car backt to the garage and had them re-diagnose the problem with the aid of the car's repair history from the MB dealer where it had been maintained for the last 10 years. The histor documented the replacement of the MAF, vacuum manifold block and both O2 sensors in the previous few months, prior to my purchasing the car. Thiese records and checking the values for these components verified that these were not the culprit. So, my mechanic (a very smart and experienced mechanic) checked the fuel regulator, vacuum hoses, etc. and he kept getting negative values for the fuel trim, even though everything seemed to check out OK. He told me that all the obvious things checked out OK. He said the next round of checks would be in the "network and chips" and would require another 2 hours of time. He said if the car was running OK (and it is), that he believes the computer is getting bogus numbers or it wouldn't be running OK. He didn't think it would hurt the car to keep operating it with the CEL on, until I wanted to spend the $ to have the rest of the diagnosis done.

Comments please! I love this car, but I don't want to live at the garage while they try to unravel this mystery.

Big Lar - not smiling.