('04 Cavalier) has been setting a p0455 code. All the components seem to be working, at least roughly: - purge valve operates, and blocks/passes when I blow on it. - vent valve, same. - canister blows through. (ie, doesn't seem plugged) - (I did change the gas cap.)
Alldata (supposedly the same as the Helm book) says the EVAP test is run when ... - The engine is running. - ignition voltage is between 10-18 volts . - barometric pressure (BARO) is more than 75 kPa. - fuel level is between 15-85%. - engine coolant temp (ECT) is between 4-30C (39-86F). - intake air temp (IAT) is between 4-30C (39-86F). - start-up ECT and AT are within 9C (16F) of each other. - vehicle speed (VSS) is less than 121 km/h (75 mph) .
We should meet that every time we run, this time of year. Instead, it usually takes multiple start/run cycles before the code sets ... AND, according to our scan tool, the EVAP test HAS NOT BEEN RUN before that. It's not that it sometimes passes: it says it hasn't been run. All the other diagnostics have, but not EVAP.
Further confusing to me, when the test does run (and fails), the freeze-frame data shows an engine temp of ~175F, every time. This is consistent with where we are in the drive cycle - the engine is warm. This seems to directly violate the ECT 39-86F rule.
I would appreciate any thoughts on any of the above.
Thank you.