What is causing this Check engine light

Geörge Kaderabek III

Asked by Oct 10, 2016 at 05:11 PM about the 2006 Chevrolet Impala LT

Question type: Maintenance & Repair

My check engine light is on and solid on my 2006 impala LT 3.9L V6. the
message center is telling me to tighten my gas cap... ive replaced gas cap 4
times now and got the car scanned for codes...got a P0455 so i replaced my
purge valve solenoid which is located on the top of the engine with no success
anything else that would cause this issue?

2 Answers


You need to smoke test the evap system to determine where the leak could be. It's the only way to isolate the problem component without replacing all the components of the system. The top two hits on identifix are the purge valve, which you already did, and the gas cap, which you already did. It could be the fuel tank pressure sensor, but without a smoke machine its jut guess work.

1 out of 1 people think this is helpful.

The FIRST thing you need to do is clear the computer after the repair. The code and light will remain on until the computer runs the diagnostic test on the EVAP system and verifies that the problem is fixed. The computer will only run this diagnosis of the system if your gas tank is between 3/4 and 1/4 full. No more and no less can be in there. So, in this order, fill up the gas tank, clear the computer, run the tank down to below the 1/4 mark, scan the computer and check that the EVAP system readiness monitor has reset. If it has reset and the code/check engine light does not return you're all set. If the readiness monitor has not reset (the EVAP monitor is sometimes hard to set) repeat the above instructions. If you get the code/check engine light back while doing this you must have the EVAP system smoke tested. That's the only way to find a leak in the system! HTH. -Jim

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