: Check Gas Cap Code

04-23-08, 02:13 PM
My 99 STS displays message CHECK GAS CAP constantly. I can clear the code, but it reappears within 2-3 days. I have replaced the cannister purge solenoid valve. I understand the message is generated when the computer interrogates the cannister pressure - checking for low pressure. Question to the forum is: where is the pressure sensor that inputs to this interrogation?


04-23-08, 03:17 PM
What code are you seeing?

Have you also checked the gas cap for proper operation?

04-23-08, 05:21 PM
The message is set anytime the system detects an open fuel tank. The cap is the most likely cause, but don't overlook the vacuum lines from the tank to the EVAP purge valve and canister. I think the pressure sensor is in the tank.

04-24-08, 04:16 PM
There was also a recall for the same code. The fault was in the tank pressure sensor which is part of the pump/level module. The recall replaced the entire tank module. GM Campaign 03038.

04-26-08, 12:10 AM
I still have the same problem, its the pressure sensor. Or at least it should be. It won't hurt anything, as far I know... but it gets quite annoying.

04-26-08, 01:07 AM
There have also been reports of rusted out tank filler necks that are very expensive to repair.

04-27-08, 12:33 PM
Well, I've been having the same problem for about a month. Tried replacing the gas cap and it actually went away for about 3-4 days, then has been back ever since. On the radiator cover it does have a sticker indicating recall 03038 has been performed (along with another one). Pulled off the cover and can't see any noticeable leaks on the EVAP line in the engine bay going to the solenoid. Have not looked under the car yet, I assume it's a steel line though up to the tank or fuel filter. So at this point, should I try replacing the EVAP solenoid if it's cheap (anyway to test the existing noid, say with a meter)? Even if the recall was performed, does that mean the pressure sensor on the replacement could still go bad? Good news is the car was smogged when I bought it in December, so I've got about 8 months to fix it.

04-27-08, 12:54 PM
There have also been reports of rusted out tank filler necks that are very expensive to repair.

you ain't kidding! almost 400 bucks for the part from the local dealer...instead i removed mine, cut out the bad sections (it was rusted on both tubes) and spliced in good quality filler hose. cost: 0$

04-28-08, 07:06 PM
Son of a gun, and just this afternoon on the way home from work the light went out again! I'm sure it'll be back in a few days though.