Hi,

I am getting an intermittent P0171 CEL pop up on my 2004 WRX. I have tried
most of the items (except 4,5,6) mentioned on this topic:
http://forums.nasioc.com/forums/showthread.php?t=475620

The car runs well, however I am sure it's slightly down on power due to this damn code.

When putting standard unleaded in, the CEL usually stays on, however if I put premium unleaded in the car it seems to 'help' the issue as the code will disappear after driving a few miles, but after couple of cycles it is back glaring me in the face.

What could be causing this?

Thanks
Jonny

 

Front 02 sensor is my guess, sorry the link isnt working for me at this time so not sure what you have tried.

 

Can't open link either but code suggests a vac pipe is split or come off causing lean running.

 

I recently had p0171 popping the CEL up a few times. Car didn't seem any different at first, then the idle became ridiculous to the point where revving at every set of lights was a necessity to keep it awake.

Turned out to be a leaky gasket on the exhaust manifold. One of the gaskets on the end of the pipe joining left to right exhaust banks. So I guess front o2 sensor was picking this up. Fuelling went up and I was doing about 250 per tank instead of 350

Also felt down on power, which makes sense - if exhaust gases were escaping before the turbo, then it wouldn't be able to draw as much air in etc etc

Simple 30 quid fix I was pulling my hair about

 

Thanks for all your help guys, much appreciated. I will have a look at the areas you all suggested and we will go from there. Hopeully it will be one of the above, especially the exhaust gasket as my exaust system is old and rusty.

Regards,
Jonny

 

Hi Guys,

Turns out it was because of a non OEM (Denso) front O2 sensor had been fitted. Swapping this for a Denso has solved all problems.

Thanks,
Jonny

 

Glad you got it sorted, but a good example of how important a Denso 02 is for others in the future.