p0171, p0174, and p0420 active codes

Question

1996 mercury sable with 3.0 ohv engine has p0171, p0174, and p0420 active codes. engine idles rough.

Answer 1

Hi there,

I the P0171 and 174 codes indicate a lean fuel mixture. When affecting both banks like this it's usually a problem with the fuel pressure or the mass air flow sensor. The P0420 indicates a problem with the bank 1 catalytic converter. I would try to resolve the mixture codes, then clear the codes and see if the converter code returns.