# 2004 Blazer **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 28, 2009, 11:07pm UTC](https://community.cartalk.com/t/2004-blazer/32564 "2009-06-28T23:07:28Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Baroness](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Baroness](https://community.cartalk.com/u/Baroness)\ **Post date:** [June 28, 2009, 11:07pm UTC](https://community.cartalk.com/t/2004-blazer/32564/1 "2009-06-28T23:07:28Z")
My Check Engine light comes on whenever the car idles - even if just at a traffic light. Had it put on a diagnostic machine at the local garage and it showed that it was an oxygen sensor. Replaced both sensors and the first time I let it idle the light came on again. Any ideas? I did find that sometimes if I removed and replaced the gas cap it would make the light go out. Sometimes the light just goes out for no reason. I tried calling the show, but after an hour of busy signal just gave up. ---
**Author:** ![waterboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/waterboy/32/764_2.png) [@waterboy](https://community.cartalk.com/u/waterboy)\ **Post date:** [June 28, 2009, 11:32pm UTC](https://community.cartalk.com/t/2004-blazer/32564/2 "2009-06-28T23:32:44Z")
Try cleaning the gas cap gasket and gas filler neck really well, It worked for me though it took about a week for it to go out, how many miles and what maintenance? as it could be air filter fuel filter spark plugs related. ---
**Author:** ![oldschool](https://avatars.discourse-cdn.com/v4/letter/o/e19adc/32.png) [@oldschool](https://community.cartalk.com/u/oldschool)\ **Post date:** [June 29, 2009, 12:39am UTC](https://community.cartalk.com/t/2004-blazer/32564/3 "2009-06-29T00:39:54Z")
We don’t want to assume the same code keeps getting set, that would be a mistake. Have you ever thought of getting a personal code reader?