Chevy HHR Network - New code in my 2009 money pit

I had sort of the opposite, P0172. It was starting WAY too rich, smoke and all, and the fuel “trim” would only correct after it got warm enough for the O2 sensors to work. Turned out the system was convinced it had 50% ethanol in the tank, even though a sample tested 11%. It should have know better, eventually, anyway. I ended up taking it to the dealer to reset the ethanol % to zero, because my scanner wouldn’t do it, nor my regular mechanic’s. After a few weeks, the car set itself to 10% ethanol, consistent with what I had been pumping.

May have been triggered by a fuel line leak and /or short trips, saying that only because another member here had a nearly identical experience after short trips and a fuel line leak. It was his thread that clued me in to check the ethanol % in the computer and in the tank.

P0171 Fuel Trim System Lean
P0172 Fuel Trim System Rich

Do you ever use E85 fuel? Or maybe accidentally, or been at a station that sells it and maybe mixed things up? Not the it should cause this problem, because 2009 and later are supposed to be fine with E85.

The air/fuel mix with E85 needs to be very different that with gasoline (which is often E10, of course.)

Obviously your problem is quite different than mine was, but after trying the other easier things, I might suggest sampling the fuel for ethanol %, and with the right scanner you can check what the computer thinks the ethanol % is, and also monitor the long and short-term fuel trim as the car warms up.

Also, it turns out that with FlexFuel, it’s especially important to turn off the motor when fueling. Donbrew has a pretty good explanation for that.