CEL P1128 and MAF

[trauh]

I've had a history of P1128 check engine lights on my 2001 C2 cab. It appeared to be fixed by tightening the bolts for the air intake on the throttle body. A few weeks ago, after 1,200 miles, it re-occurred so I took it to the dealer to have it checked. They diagnosed as needing a new mass air flow sensor, which I then replaced. It feels to me like the car is faster and it definitely gets better mileage since then.

Not sure what to take out of this, although I wonder if the leaking air intake could have damaged the MAF. I elected not to try to clean the MAF, given my long history of issues. Hopefully this ends the chapter for my nagging CELs! For those of you with similar issues (and there seem to be several), its worth noting the MAF replacement.

[rcg412]

FWIW. This is all on a 2001 996C2. When I got my first CEL (p1128) it was due to the rubber housing around the air filter not being seated correctly... hence a "Massive air leak" was occurring. Dealer fixed.

After fixing the rubber housing, the car worked great until a few weeks later when the CEL came on again... another trip to the dealer and was due to oil cap not being tight, so tightened it. This never sat right with me

When the CEL came on a third time, took it to the dealer and diagnosed as a MAF... replaced and have not had a reoccurrence with ~3000 miles (knock wood), my gas mileage and idle are also improved. When I asked the dealer why didn't he detect the MAF in the first place, he said it was due to the air leak bringing in dust/pollen/etc and getting in the MAF.

Nonetheless, I have found on that CELs have a nasty tendency to come on usually after a service(mine came on ~ 500 miles after 45K service). Which leads me to believe it may be due to dust, contamination when they change the filter.

Hope this helps. Ross

Edited November 21, 2005 by rcg412

[PTEC]

When I asked the dealer why didn't he detect the MAF in the first place, he said it was due to the air leak bringing in dust/pollen/etc and getting in the MAF.

For what its worth, an air leak can disguise a failing MAF. Air leaks cause the MAF to read less air, failing MAFs almost always read more air. Therefore you can have a failing MAF and a big enough air leak to offset the MAF reading high. Any technician sees fuel adaption towards positive and thinks air leak immediately. Technician finds the air leak and corrects it. Now what should have been done is a test drive and recheck of fuel adaptions, which if the MAF was failing, would be going towards negative and would indicate the MAF as on its way out. Unfortunately technicians dont get paid for test drives so the motivation to thoroughly ensure a repair is pretty low.

[gcp]

Here's a sample of one opinion....for whatever it's worth. The air filter being clean "at all times" is very important in my book. Since I cleaned my stock filter and reset the CEL the problem disappeared.

Since then I've installed an EVO induction system and still no CEL light. I'd say make it a habit to keeping the filter clean and a lot of these problems of failing MAFs my disappear.

I have a suspicion that most dealers/techs tend to throw parts at this problem and if it doesn't work, oh well, lets keep trying/charging more in hope of a solution. It's beyond me that they do this with a clear conscious, being that they have access to costly high powered trouble shooting computers <_<

Thanks,

Edited November 22, 2005 by gcp