This may help if you have a similar experience. I started out this morning for a doctor's appointment and noticed the Service Engine Light on. Oh goody, what does this mean. The next service is over 12,000 miles away. I checked the manual and it said it was an emissions problem. Oh, great, the dealer is an hour and a half away. Well, I remembered that I had similar problem with my Alfa and the gas cap was loose. I checked the gas cap and it was tight, but I just loosened it and retightened it and the light went out. problem fixed. If you have similar problem try this solution before traveling to the dealer.

 

I had the service light go on within 100 miles of having the car..........I brought it to the dealer and they said tighten the gas cap after you gas your car. I was like mmmmmm....I haven't even used the first tank up so how can that be the problem.....So they put the computer on my mini and it was a faulty fuel rack or something with the fuel injectors.........So that might be the problem be not always........



tony

 

My dealer told me that 9 times out of 10 the reason the Service Engine Soon light comes on is because of the gas cap not being tightened. However, I'd be careful with this, as sometimes it can mean that carbon monoxide is getting into the cabin of the car. Don't screw around with this, check the gas cap, if that doesn't fix it get it to your dealer, with the windows rolled down.

 

I agree that you should have the dealer check out a problem that lights up the check-engine light.

I don't see how a loose gas cap could cause carbon monoxide to enter the cabin of the car.
This car should produce almost zero carbon monoxide in the firt place, and it all comes out the tailpipe.

The reason the MIL light is being lit is because the computer is required by the federal emissions rules to do a vapor-recovery leak check periodically.

It pumps a little air out of the fuel tank, and measures how long it takes to leak back in through a tiny hole. I think it's 0.01 inches in diameter.

If it leaks in too fast, there is a break in the system somewhere and you should look into it so that fuel vapors don't pollute the environment. (Really a little bit of pollution I know, but a bazillion vehicles adds up).

If the gas cap is loose, it leaks back in fast, and the MIL lights up. The computer can't tell where the leak is, so it asks you to go into the dealer and have it checked out.

Sorry for the lecture, but I honestly think some people like to read about how these things work. (That's what I hear anyway)

So, tighten the gas cap and motor-on. If the MIL lights up, take it to the dealer, but I don't think you need to drive with your window down.

 

say, my 04 has a light for Gas Cap. I assumed that when it failed the evap test this light would go on instead of the MIL. Am I wrong? This is the first OBD II car I've owned with a separate lamp for Gas Cap.

My wife left the cap off her Jetta once and quickly got a lamp. She didn't think about the gas cap and after a couple of days took it to the dealer and they tighten it for her. Oops. Unfortunately, that car was prone to overly enrich the fuel on any failure and soon afterwards the front O2 died.

Lesson:
1. Always check cap first.
2. If you don't have means to fix the fault yourself, quickly have it repaired or you may be looking at other repairs.