hi guys,
prior to registering my car, I had to perform an emissions check and from that, the gas cap test failed (there was NO check engine light on prior to the test). bought a new cap from my local jaguar dealership and swapped it over. I noticed that with the old cap, it clicked 3 times with a single rotation but the new cap only does a single click. a few days later, the check engine light comes on w/ the p0442 code (small leak). made sure the cap was on correctly and after a dozen or so starts, the light was still present. I then swapped over the old cap but after a dozen starts again, the light is still on. any idea? I'm thinking of gong to the dealer and telling them I got a faulty new cap. also, I'm assuming the check engine light would self correct once the new cap was put in, am I incorrect about this or does it need to be manually cleared?

thanks

 

Have you checked carefully for damage to the fuel cap's mating surface at the filler? Perhaps a rough spot or gouge from a pump nozzle.

 

thanks for the suggestion. just checked it and mating surface is good. will have to stop by the dealership and get their input on it but if anyone else has any feedback, please let me know. thanks.

 

Have you tried clearing the code? Most auto parts stores will usually do it for you, if you don't have a scanner. I had a similar small Evap Leak code caused by pump attendant (NJ) not putting cap back on fully. It didn't show up right away, so it was obviously an intermittent thing, but when it did, it never cleared itself. Then I cleared the code and I haven't seen it since. Been over a week now.

 

I have not cleared the code myself but I confirmed w/ the service department that the code would auto clear once the appropriate gas cap is installed. which brings up my conversation with the parts guys behind the counter...I ordered the incorrect gas cap based on the part number that I believe I found here on this forum. he said new correct cap was $66 but with my discount (I set up an account with them), it would be $54. asked about price matching and he said he would only match prices to other GA shops because out of state shops would charge shipping. told him thanks and went on my way.

so I've placed an order yesterday with brit-car for a new gas cap and that gave me an excuse to oder the front fender/splash guards along with it.

what's funny is that the code cleared today using the old gas cap.

 

Sounds like it may not be the gas cap, though that would be an easy and cheap fix. This code relates to a small evaporative leak, and usually loose gas caps are the issue, but it could also be the the purge valve, or leaking O-ring in the carbon canister or many other places in the system. If the cap does not fix it, the best way to DX is with a smoke test...That will quickly identify where the leak is.

Good luck,
DC

 

I think your first statement is not entirely accurate. I think it clears automatically but not immediately. I'm not sure the algorithm, but it's either going to be number driving cycles (start, drive some distance), miles, or just stop/start cycles. To add to confusion, I believe the evap system has a pump that self-tests when the vehicle is off.

 

Correct, that is what I meant to say and experienced. Today was my longest one way trip of 40 miles and it finally cleared at the next restart...had about a dozen restarts prior but all were shorter trips of less than 15 miles. Will install the new cap once it arrives but at least for now, no more check engine light.

 

EVAP codes can take several drive cycles to clear by themselves. Further, on some cars the ECU only tests for compliance at a certain level of gasoline in the tank.

So, be patient if the light comes on again.