View Full Version : Info regarding "check gas cap" message....

06-14-12, 08:07 AM
Well, I'm sure it has been discussed, but I've tried searching several times and come up with nothing in my searches.

My maggied V has started giving me the "check gas cap" message about once a tank or so. It's only gone off 3 times.

It may be related or coincidence but it seems like I'm getting a bit larger drop in idle when pulling up to stoplights. Very random but once in a while dropping to like 600rpm for a second or two.

Unless the gas cap itself needs to be changed, I was wondering if this could be related to another area of the fuel system, like the evap system or something else? Or just a random vaccuum leak. I'm just not sure where the sensor is in the system to "know" to check the gas cap.

Any ideas would be great.



06-14-12, 09:00 AM
Ok, I did a google search and the threads popped right up, including this one that was resurrected last month:

This has a great diagnostic if I was getting a DTC but so far no DTC, just the check cap warning.

I'll try some of the other threads, too.


06-14-12, 12:41 PM
Did you check the codes. The MIL light doesn't turn on for all codes.

06-14-12, 04:38 PM
I didn't check codes. I need to sell my Autotap and AKM cable from my '96 Impala SS days and get either a scanner or purchase HPTuners.

I did, however, pick up a new gas cap at O'Reileys for $20, AC Delco GT303 that includes the lanyard. It looks like the exact duplicate. I believe the problem was the seal was just worn out. Here is a cell phone pic but you can see the second seal is just laying flat against the first seal. It lost all memory.

New cap on. Now, I was looking at the old one. With a paperclip you can hook the green seal and pull it off. The seal is u shaped, so the bottom side becomes the top if you flip it over. I would think in a pinch you could just flip the seal and get several more miles out of it before having to get a new gas cap.


07-16-12, 01:45 PM
Now I'm getting Code P0442, and it says "small leak".

I have the troubleshooting guide, linked above.

However, does anyone have a good source for a smoke emitter than can be used to check the system for leaks?

Or, any good places to check visually for cracked hoses/etc.?

My car does have a maggie, so perhaps there are other sources for vacuum leaks? I think the magnavolt or whatever is referenced off the brake booster line. Is that isolated from the evap system or could any leaks there cause it as well?

Just looking for ideas before I start crawling around underneath, etc.



07-16-12, 02:24 PM
You have a voltage booster and have not installed the Racetronix kit or a new fuel pump, right?

07-18-12, 10:08 AM
^^Correct to my knowledge. Everything was installed when I purchased the car. The setup has been running without issue for 40k+ miles. My guess is I have a vaccuum line that is dry-rotted or the charcoal cannister is cracked (have seen in other posts) or something similar.

Is there something that the re-wire or different pump do for the system holding vaccuum after shutdown?


07-18-12, 11:48 AM
If you had a voltage booster, I was going to say that there was a small chance you had melted/fused the connector next to the pump and damaged some of the plastic tubing leading into and out of the fuel tank. That would've been a major fire hazard, and you might've seen a little bit of fuel dripping onto the ground.