Originally Posted by
zip439
What you were told about the secondary air pump coming on after long slow idle doesn't make sense to me. Adding air to the exhaust increases burning and heat which the
O2 sensor interprets as a lean condition (excess oxygen), giving low voltage to the PCM/ECU and thus the PCM will increase short term fuel trim. Thus adding more oxygen to an already lean condition as noted by the short fuel trim is the wrong thing to do. IF I INTERPRET THIS CORRECTLY!
If the 02 sensors are operating correctly and the PCM is responding correctly giving you the increase in short term fuel trim the voltages the 02 sensors are producing should be 0 to no more than .5 volts. Checking the voltages of the
O2 sensors against the short term fuel trim could help you determine if the PCM is going bad as you suspect.
On one of my n/a crossfires I have a aftermarket secondary air pump that is pretty loud and I can tell you it most certainly does come on at times during idle after the engine is hot. Iwill try and find the time to brush up on the secondary air system this weekend in case this is the issue that is causing his CEL.
Edit: when the pump comes on at idle after the engine is hot (sitting at a stop light) I'd say I have never heard the pump run for more than 2-3 seconds, if that helps at all.