06, 2LT, 170k
First cold night in AZ and an old issue has returned. When the night time temp drops below 60 I get a CEL and a P0442 code.
This does not happen during the summer.
This only happens once per tankful of fuel, and, it happens every time around 1/2 tank.
2nd issue, I have no CHMBL, but my cruise control works.
I used to have the light with LED's installed
Any ideas? My brain has hit a roadblock.
Thanx

 

Aside from the fuel cap leaking here are the othe culprits to look for

https://www.obd-codes.com/p0442

I had an issue and when I tested the Evap purge valve under the , it had failed I should be in the closed position when not on.
I could blow air through both directions.

 

The p0442 test only runs at night when the fuel tank is between 1/2 and 3/4 full. Being cold sounds like a seal is shrinking.
It's CHMSL. Took me a while to figure it out. Brake vs Stop.
Did you leave a resistor in. Why did you break the law by removing the CHMSL? There is resistance in the circuit. It is asking for trouble not having it.

 

I did not remove the CHMSL. It just stopped lighting up which is why I'm at a loss as of why.
I never installed a resistor in that circuit.
It worked for over a year with the LED's and then just stopped.
I will reinstall the incandesent bulbs and see if that fixes the issue.
BUT that doesn't explain why the cruise works.

 

The gas cap was replaced last year with one from the Chevy dealer.
Which seal?

 

Seals all over the EVAP system.

 

The seal at the evap canister under the car by the fuel tank.