Thought I should start a new thread as this is a slightly different question. Is it possible that a leak in the EVAP charcoal cannister system could cause P0171 without the normal P0440 EVAP code? I ask because my friend's dealer told him he needed a new charcaol cannister and he allowed them to do it. I'm not sure how much time elapsed between that work and the appearance of P0171 but I am going to find out.

 

Charcoal cannister s related only to the P0440, P0441 and P0446 codes.

However, part of the evap system (you know all those hoses you see when you take off the engine cover right on top of the manifold), well a few of those hook up into the top of the throttle body. You should check for any leaks on those.

With the P0171, I used to run a lot of fuel injector cleaner in Mexico (I used to have cases of techron and in my little storage area downstairs at my apartment that I would get at Costco). Despite as dirty as my MAF and intake system would get (and I would clean), I still blame many of those P0171 woes on the gas, because despite having practically the same intake setup, I have seen a lot less P0171 errors running U.S. gasoline (even with the 10% ethanol in Florida), both before and after changing out my A/F sensors not too long ago. Injector blockage/fuel line pressure is one of those things mentioned in the service manual under the P0171 codes.