Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Good morning, when PO455 sets it means there is a large leak in the evap system or a problem with the evap purge system.
The most common cause of this is a bad gas cap. If you haven't already I would replace that first.
If the gas cap does not solve the leak the vehicle will need to be smoke tested. This is a procedure where a special machine is used to introduce smoke into the EVAP system to find the leak.
I'll post manufacturer troubleshooting info on this below for your reference.
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