Jim Grant's Tech Tips

'99 Chevy Astro, Loose Gas Cap Code

Q: The Engine Light on my ’99 Chevy Astro van keeps turning on. I have it checked and the computer is reading a code 442. They tell me it is my gas cap it is not tight enough and they erase the code and tighten the gas cap. Then a week later it comes back on and back I go to the shop. What else is going on or what can I look for? It rides great and has full power. What’s happening with the check engine light?

A: Are you having a problem tightening the gas cap on your vehicle? Have you been shown just how tight the cap should be? Do you hear and feel that gas cap click when it is tight enough? The computer code you’re providing indicates that there has been a small leak detected in your vehicle’s evaporative emission system. In plain words, your gas tank, hoses or vapor system for the gas tank is not sealed properly and gas vapors could be escaping. It only takes a visit or two to the shop before the customer becomes savy and learns the importance of correctly tightening their gas cap. If you have this part under control then there is another problem that is not being addressed. A loose gas cap can set this code. In addition, a defective gas cap can set this code or a small pin hole (about the size of a sewing needle), loose hose clamps and a variety of other little things that could cause a small leak. The computer in most all ’96 and newer vehicles runs a test on the gas tank and related vapor system to be sure it’s sealed correctly. Your vehicle is failing this test. The computer is turning the check engine light on to alert you to this system problem. The gas cap is always the first check to be made, but if the problem is reoccurring and the gas cap is tight, additional diagnosis will have to be performed.