# Mercedes 1997 E420 Smog question **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mercedes-benz, e-class\ **Created:** [December 8, 2012, 5:32am UTC](https://community.cartalk.com/t/mercedes-1997-e420-smog-question/75997 "2012-12-08T05:32:23Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![TastydonutHD](https://avatars.discourse-cdn.com/v4/letter/t/58956e/32.png) [@TastydonutHD](https://community.cartalk.com/u/TastydonutHD)\ **Post date:** [December 8, 2012, 5:32am UTC](https://community.cartalk.com/t/mercedes-1997-e420-smog-question/75997/1 "2012-12-08T05:32:23Z")
Hi, I live in California, and my dad just got his hands on a Mercedes 1997 e420, and has fixed up the minor problems. It runs good, but to sell it he needs to take it to the Smog check. Does anyone know how long it’ll take to reset the computer for it? I know there are strict regulations in California. Any help would be appreciated. Thanks! ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [December 8, 2012, 6:31am UTC](https://community.cartalk.com/t/mercedes-1997-e420-smog-question/75997/2 "2012-12-08T06:31:21Z")
I don’t know the reset procedure for your ECM, on most cars it usually takes several days of driving, a Mercedes expert would have to chime in. You are right that it has to reset. The smog check place won’t test the car until it is. In the way of general guidance on Calif smog testing, suggest you Google “How to pass a California emissions test”. There’s some good info there from a couple of the sites. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [December 8, 2012, 8:14am UTC](https://community.cartalk.com/t/mercedes-1997-e420-smog-question/75997/3 "2012-12-08T08:14:08Z")
Why do you feel there is a problem? Is the Check Engine Light on?