I had a friend bring his OBDII Scanner to check my codes. This CEL light came on a few weeks ago and after being parked over night went away. It initially came on when I did a 6K plus rev for a friend to hear the exhaust. It has now come on again yesterday and been on for almost 2 days time. When my friend checked the codes I got a P0171 and P0420. I've read that the 0420 can be fixed with an anti-fouler for the O2 sensor. When researching 0171 I saw it could be a MAF problem, O2 sensor problem, or vacuum hose to FPR disconnected. I also saw people said the 0171 is difficult to locate and whether or not other codes were thrown. So being that I have both codes being thrown and the 0420 was thrown twice im unsure whether these two are together or seperate from each other. Any help is much appreciated thanks.

 

p0171 is too lean. Too lean means either too much air or not enough fuel. Possibly low fuel pressure or an air leak after the MAF sensor. Do you have a wideband on the car to check your own AFR? p0420 is for the cat converter. Do you have a test pipe or do you still have the stock converter? If you have a test pipe than the quick fix is a spacer for the rear o2 sensor. Is the car tuned? Be careful with the too lean issue. If you run the engine very lean you will cause engine damage.

 

I have perrin cat it may just be a resonator test pipe cause its not much bigger than the pipe. Thats for the 0420 which ya i believe the defouler will cure that. As for leaning, I have a Innovate wideband and my AFRs are fine. I idle at 14.5+/-0.3. When I do a 3rd gear pull or just about any gear for that matter at WOT I starting at 11.3 +/- 0.2 and decreases to about 10.7+/-0.2, which I would think if anything I am running a bit rich. It has tune that is a protune. That being said I am unsure what shop did it. I have HKS intake, greddy intercooler, headers, greddy turboback, perrin cat/resonator.

 

Yea space the rear o2 out, P0420 done. As for the P0171 sounds like your AFR is on point. If you have access to a scanner or evoscan you can watch your (STFT) short term fuel trims and (LTFT) long term fuel trims. The short will always be moving and should stay within +/- 10. The LTFT shoud be ideally 0 but will stay more steadily at +/- 10 and that is acceptable. If those numbers are in spec than you are good to go especially since you can monitor additionally with your wideband. A boost leak test wouldn't hurt just to make sure no unmetered air is getting in on occasion. Sounds to me like you do not have any real problems.