allezdude

Autozone downloaded the error codes from my 98 W210 wagon and they were:

P0170 fuel trim malfunction- Bank 1

P0173 fuel trim malfunction- Bank 2

Car drives normal- 42,000 miles. Based on previous posts it sounds like the mass airflow sensor. Could it be anything else? And I'm assuming only MB dealer can reset the adaption values once the sensor has been replaced? Thanks for your help.

mbtech208

First check for any vacuum leaks, if there are none, your mass-airflow sensor is bad. You are correct, the dealer will have to erase the codes and reset the fuel trim adaptations.

fastneutron

Hi MBTech,

I also have the same code P0170 and P0173 on my C43. The CEL came back on after 500 miles from clearing it the first time by changing the Bank2 Sensor 2 O2 sensor. I took the MAF sensor off and could not find anything wrong. The MAF sensor was actually just changed 8,000 miles ago because the last one got damaged by the fluid from the aftermarket air filter. My mechanic (Chino Hills AutoHaus) told me that it could be that I didn't change the other O2 sensors and the other O2 sensor could now be lagging as far as response compared to the one I changed out 500 miles ago.

Could he be right? My car is now over 100K because of commuting from LA to San Jose. I just don't see changing something that it is still okay, especially because of the labor and cost involved with changing the O2 sensors.

I've already reset the P0170 and P0173 once and it came back on again after driving from Ontario Airport. Supposedly, my MAF sensor should be covered for at least 1 year or 20K miles warranty, but I'm not going to take it to the mechanic if he'll just tell me to change the rest of the O2 sensors although it is not necessary.

I might just try and clean the MAF sensor with intake/throttle body cleaner by STP. What do you think?

Thanks in advance.

eddieo45

I got some MAF cleaning instructions that recommended Simple Green and alcohol (do a search); I still haven't solved my CEL issue, which, in case you never saw my post, car runs fine, maybe slightly hot, but CEL on. Replaced MAF and it ran BAD, so I put my old MAF back in. If any of you gets to the bottom of your CEL, please post!

blackmercedes

In order to verify the diagnosis, you need to read the adaptation values. If the fuel trim adaptation is 1.32, the compensation is for a faulty Air Mass Meter. If it's less than 1.00 (.6x) then it might be the fuel pressure regulator.

Install a new AMM and recheck the adaptation values if the original alues were 1.32. They should be fine if the AAM was the required part.

eddieo45

how does one read the adaptation values? is it something my independant mechanic can do, or does it require MB laptop? also (warning, potential dumb question coming), how should one check for vacuum leaks?

blackmercedes

Yes, if your indie has the SDS (Star Diagnostic System) which lots of indies do. If your mechanic does not, he/she will be severly handicapped in doing any real diagnostic work on your car. The SDS is required for all kinds of diagnostic work, inclusing all emissions systems, AC/ACC systems, electronic trans control and mechanics, and so on.

fastneutron

I'm going to install the MAF on my other C43 to see if it is really the MAF. If not, it sounds like it could be the fuel pressure regulator. I'm hoping that it is the MAF because it is still under warranty.

blackmercedes

If the car is in warranty, then simply take it to the dealer and they'll diagnose the problem and fix it.

eddieo45

I think it's just his MAF that's in warranty...I think (what do I know) that it's a worthwile experiment (putting the "good" MAF in the "bad" car), I replaced my MAF, and it got worse! I still don't know what's wrong, but it's pretty clear it's not the MAF...

blackmercedes

I have never heard of anyone greatly extending the life of the Air Mass Meter through cleaning. It would seem to be a short term solution, at best. The problem is that you might extend it's life to just past the point of it's warranty.

A mechanic that does not verify the diagnosis before blowing YOUR money on parts is one not to be returned to. A whack of O2 sensors can be expensive, and what if they don't solve the problem? Do you get a refund?

The proper procedure would be to read the values, and if high (1.32) then replace the AMM with a fresh unit and drive the car. Recheck adaptation values. If they are normal, presto! Problem solved. If not, reinstall AMM and begin new diagnosis. Mechanics that just start swapping parts on your dime are not worth your time, and will only run you way more money than you would ever spend on diagnosis time with a good tech. If he properly diagnoses the problem as the other O2 sensor, verify that this means that your money has fixed the problem. No more games of throwing parts and cash.

99% of the time 0170 and 0173 are either an Air Mass Meter or fuel pressure regulator, depending on adaptation values. Depends if it's compensating lean or rich.

Are you still using the Non-OEM air filter? They (K&N, etc...) are AMM killers, and might preclude the new AMM from being covered under warranty.

teky

P0170 fuel trim malfunction- Bank 1

P0173 fuel trim malfunction- Bank 2

i put it down to the EVAP canistor purge valve
other faults that cause them codes are o2 sensor/intake leak/fuel pressure-pump/injectors

Fathead

I agree with BlackMercedes.
Go to a mechanic who has the correct equipment.
I got caught in the same loop 6 months ago w/ my 98 W210. Same CEL, same codes. After screwing around for a couple of weeks with an poorly equiped indie, I took it to the dealer. Replaced all 4 o2 sensors & MAF sensor in 1 day.
The car has run great ever since; forced indie to give me a refund.
Here's a kick in the head: the dealer was about the same price as the indie.

eddieo45

hey fathead (no offense), how much was your trip to the dealer? my indie hasn't charged me anything for the diagnosis or the AMM/MAF swap experiment.

Fathead

The MAF was $450 installed and my recollection is all 4 O2 sensors (use caution, my indie's generics Bosh did not work) cost an additional $600 for about $1,100 complete.

I have no regrets. The car has run perfectly ever since.