ncmudbug

I started a thread about this situation a while ago, but I started a new thread because I screwed up the title of the original one.

To recap, I was getting two sets of P0170 and P0173 codes. It was right after I had the tranny fluid changed and I suspected that the codes and the fluid change may be related.

I was advised that it was likely because the MAF was dirty. I cleaned both the MAF and the throttle body and that seemed to be the end of it (this was 7/20). The car drove smoother and didn't throw any codes.

This afternoon, Mrs. NCMudbug came in and announced that she had a CEL and it turns out to be the same two sets of P0170 and P0173.

Does anybody have any ideas of what to do next?

Glyn M Ruck

If you are satisfied that you have no vacuum leaks including the brake booster then it's possible you have O2 sensors getting tired or a MAF that is failing.

ncmudbug

Thanks, Glyn. Is there anyway to tell which one is the problem?

Glyn M Ruck

Fuel trim codes are typical of MAF but sometimes you get no codes. Same goes for O2 sensors. They need to fail to throw a code. Just cycling too slowly will not generally throw a code.

This is where a dealer has an advantage. they can try things from the parts dept.

ncmudbug

Thanks again, Glyn. It would just my luck to buy the one I don't need first! It may be worth taking it to the $tealer .

ncmudbug

Well I did some poking around and saw what the $tealer charged for a new MAF so I bought one from Autohaus. Now if that ends up not fixing the problem, is there an intelligent way to change O2 sensors (i.e. front first, then rear or rear first, then front, etc.). Or should I just change one at a time till the problem goes away?

BTW - The codes came back but this time, only the P0170 showed up (twice as usual) rather than both P0170 & P0173. Is there anything I can take away from that?

Thanks!

Glyn M Ruck

P0170 Fuel Trim Malfunction (Bank 1)
P0171 System too Lean (Bank 1)
P0172 System too Rich (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)

Does not tell you much. MAF takes a while to auto calibrate.

Regarding O2 sensors. If the problem persists after new MAF then change both upstream sensors. The downstream ones just evaluate Cat performance. They have nothing to do with mixture control.

ncmudbug

Thanks, Glyn!