Have a 2001 911 and get ECL at exactly 3/4 and 1/4 fuel tank levels
Autozone decoded as 1133, O2 sensor Bank 1 and 2 Sensor 1
And 1126, fuel trim adjustment - bank 2 system too lean.
Any ideas where to go from here? Work with a reputable mech, but would like some idea what's going on and what a reasonable cost be to fix. Car runs great and passes emissions.

 

You have to be careful. P1XXX codes are manufacturer specific.

My reference for these codes;

P1126 - O2 sensing adaptation, lower load range, bank 1

P1133 - O2 sensing adaptation, lower load range, bank 2

Probably the MAF. While I don't hold out much hope some have reported cleaning the thing helps. It shouldn't be dirty unless you are running an aftermarket air filter and it uses oil or is letting unfiltered air into the intake. Oil or dirty air will foul the MAF.

There's a quick and dirty test you can do. Carefully disconnect the MAF from the engine wiring harness. Clear the error codes, which also resets all fuel trims to their defaults. Drive the car. Be aware the CEL may come on and the PSM and ABS may emit error messages/warnings. This is because the MAF is not connected.

Drive the car as you have in the past and see if the CEL and error codes reappear.

If the engine starts acting up, running rough, whatever, shut the engine. The problem ain't the MAF.

If the error codes stay away connect the MAF, clear the codes again, and road test the car. If the CEL and errors come back,...

Oh, after the MAF has been reconnected the ABS and PSM errors/warnings if they remained after the engine was shut off and then restarted should go away after a couple of engine warm up cycles.

 

Thanks much. I reset faults and removed and cleaned the MAF with MAF cleaning solvent I got at PEP Boys. Ran 40 miles and so far no CEL. Air Filter was pretty clean, 6 mos old. The MAF did appear dusty. Car does start a bit smoother and runs great. Think I'm on the right track. Thanks again.

 

Well, for the MAF to be dirty enough to affect its operation is a sign the filter is not filtering. Are you sure the filter element is installed correctly?

I have driven hundreds of thousands of miles and not had to clean the MAF in either car at all. With a properly functioning stock air filter/box the MAF does not get dirty.

 

Thanks again, ordered another OEM filter and checked the integrity of the box. Up to 70 miles with no CEL. I think you are on the mark. Will have a mech check for leaks if it comes again.

 

Cleaned MAF and replaced air filter. ECL light back on again when fuel tank level hit 3/4 with same codes. Would replacing the MAF with a new one be a reasonable step or should I submit to an expensive analysis. Car still starts and runs great.

 

I had to have mine replaced, cost around $700. I too reset then code then went a week thinking everything was fine then it popped up again. Had it replaced and fuel mileage went up and everything is fine 6k miles later..Mine was replaced with less then 50k miles on the clock

 

Replacing the MAF on the 996 is dead simple. You do need a special security torx bit to remove it, however. Look on eBay and you can get the MAF sensor for around $300. Much less than the $700-$800 some places want.

Matt