Earlier this week my check engine light came on. I had the computer scanned and it said 2 codes and then showed P0442. I have a 2007 C6Z06.

I then did some research on this code and learned it is a small leak in the fuel vapor system.

P0442 Evaporative Emission (EVAP) System Small Leak Detected ECM DTC P0442 in Engine Controls

The number one cause that everyone says is the gas cap. I have checked this but the engine light is still there. I never did clear the code when I scanned it, I guess I should have. I have since started the car 6 or 7 times and have driven 50 or 60 miles.

I have a number of questions that hopefully I can get some answers to.

On my gas cap, once it is on, I cannot grap it and pull it off, but when I do rotate it CCW to remove, it does not take much force. On a typically good gas cap, does it take a good amount of force to remove it? My gas cap appears to have no obvious signs of wear or damage.

How much is a new gas cap from GM? Can I just buy a GM replacement at the local auto store?

Do all scan tools allow you to clear codes? The one I used at Pep Boys had a button called reset, which I pressed but it did not clear the code from what I could tell.

The reason I am questioning whether it is the gas cap is I recently had my heads removed and rebuilt, so the engine compartment has been taken apart. Might I have a leak in a line? The question I have is where do I look? Which lines belong to this system?

Does anyone have a diagram of this circuit and pictures of where the components are?

Is this statement true, I saw this in another post? "The EVAP system does not test for leaks with ignition cycles. You need to be cruising at speeds generally over 40 MPH with between 15%-85% fuel level for the EVAP system test to run." If so, when I had the computer scanned, I had less than 15% fuel. It then retighted the cap and filled my tank up, so I think I am currently over 85%.

I have a track event next week and want to get this resolved.

Thanks for your help.

 

As far as the gas cap question goes, it should take a little force to break the seal. Not sure how much they cost, but the reason I am responding is whenever your engine service light comes on and you have tried a fix, it wont reset until you disconnect the positve terminal of the battery for about 15 minutes, then reconnect battery cable, if light stays off after road trip, it cleared. Im thinking you probably tried this but just in case you havent, hope this helps.

 

I have not tried this. I was under the impression that disconnecting the battery would not necessarily clear the code assuming the fix I tried worked. The computer needs to run the test for this a few times and get back no errors before it would go out.

 

"The computer needs to run the test for this a few times" ...thats what the road test is for. good luck.

 

I noticed that my gas filler tube does not have that little flap valve that I thought was once there. Do our cars have these? This is the little flap that you push the gas nozzle down through.

 

No flap valve in filler tubes anymore, and I did notice my cap has real good tension on it. Did you try to remove battery cable and did the error show back up afterwards without even starting the car?

 

Yes, I removed the cable from the battery and now the check engine light is gone. We shall see.

 

Little later I know but hey
hold down the options button then tap the fuel button 4 times
Use guages and trip buttons to scroll through the menus
Hold reset on a code and it clears it
That's how I turned off my check engine light whrn i got the p0442 code
Press e/m to exit the menu

All these buttons on the dash to right of steering wheel

 

This is the C6 forum. What you described only works on the C5.

 

​​​​​Where's the hand to face emoji...
My mistake man.

No such feature on the c6 tho? Hm...
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