service engine light error code indicates low level emission error related to fuel vent / recovery system.
2003 Trailblazer EXT
Need to find location of fuel vent valve and solenoid to check them out.
Daily re-seating of gas cap seems to extend the time intervals between error light coming on, but local mechanic thinks vent valve might be dirty and sticking open...

 

try a new gas cap first

 

I tried a new locking gas cap and it captures the fill neck tabs less securely than the original equipment cap.

 

I am hoping someone can direct me to a photo or diagram of the fuel system components so I can minimize my time freezing under the vehicle and/or disassembling the wrong parts...