2008 Chevy Impala LS 3500 motor 2 codes

Question

PO455 code followed a month later with trouble starting when engine is cold and PO172 code.

Answer 1

Hi there

The P0455 is for a gross evap leak. This will not cause hard starting unless the leak if from the purge valve to the intake. Otherwise, you need to do a smoke test to locate the leak.

The second code, P0172 is for a rich fuel mixture on bank 2. This could be the result of a faulty front O2 sensor or a leaking fuel injector which might cause the hard start. I have also seen this issue with a bad mass air flow sensor as well.