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P0174 & P0171(pending)


Be Gentle I'm New Here
Feb 2, 2021
Windsor Ontario Canada
1997 Ford Contour 2.5
First, I got engine code P1151, replaced the Bank 2 upstream 02 sensor.
Then I got the other 2 codes mentioned, so I replaced the Bank 1 upstream 02.
I had reset the codes the day before replacing the 2nd 02 sensor and the two codes popped up again after replacement.
It’s only been a few KM since driving but if they pop up again does anybody have any idea what they could be if not 02s?
I keep reading air leaks.. but it has 107,000km and it’s in good shape under the hood. Nothing cracked from what I can see and I hear no noises.
Also, OBD shows MAF and 02 sensor voltages are all correct.

I might be too soon with my post since the codes in the system may have already been wanting to display before I swapped the 2nd 02 and they might not come on again.. but has anybody else successfully tackled these codes ?? Thanks


Oct 31, 2015
Alberta, Canada
Could be catalytic converter issues. My car has had the cats removed and always throws these codes. Both of my 02 sensors are and will always be dirty due to the lack of cats and contaminating the sensors.

However, also check your pcv valve, EGR and your air intake connections as this code is reading a lean mixture, thinking it’s getting too much air from somewhere.