# 2003 GMC Sierra 1500 P0455 **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** sierra1500, gmc\ **Created:** [April 7, 2018, 5:31pm UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154 "2018-04-07T17:31:19Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![RobSexton](https://avatars.discourse-cdn.com/v4/letter/r/e56c9b/32.png) [@RobSexton](https://community.cartalk.com/u/RobSexton)\ **Post date:** [April 7, 2018, 5:31pm UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/1 "2018-04-07T17:31:20Z")
I have a check engine light that has been coming on & off for about 2 years now. The code is PO455 I have had it in two shops & all parts related to this code replaced, some more than once. It has been smoke tested a number of time showing no leaks. It seems that when I fill up with gas, the light goes off and within 100 miles , the light comes back on once in a while. Do you think flashing the computer will get the light to stop coming on. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [April 7, 2018, 6:44pm UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/2 "2018-04-07T18:44:10Z")
No, flashing the computer is a sign that the guy is desperate and/or clueless A word to the wise . . . that code doesn’t specifically mean you have a leak It means a sufficient vacuum couldn’t be generated and maintained in the evap system It could be a leak, a purge valve which cannot draw a sufficient vacuum, or several other things If it is the purge valve, a smoke test will not reveal it to be the problem I feel whoever has been working on your truck doesn’t understand how these codes are generated, and how to verify that the evap system is working properly ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [April 7, 2018, 8:40pm UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/3 "2018-04-07T20:40:13Z")
Agree with @db4690… Even if I give him the benefit of the doubt regarding his skills… Your mechanic may not want to replace a cheap simple sensor that is a bear to reach. There is a sensor on top of the gas tank that measures evap pressure. If that hasn’t been replaced, it may be the problem. It is in the top of the fuel tank. You need to drop it to reach the sensor. ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [April 8, 2018, 1:01am UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/4 "2018-04-08T01:01:10Z")
Flashing the computer will not help, I bought a gas cap from the dealer to cure that code for me, also cleaned where the gas cap meets the filler. ---
**Author:** ![RobSexton](https://avatars.discourse-cdn.com/v4/letter/r/e56c9b/32.png) [@RobSexton](https://community.cartalk.com/u/RobSexton)\ **Post date:** [April 8, 2018, 2:24am UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/5 "2018-04-08T02:24:59Z")
The pressure sensor has been replace two time, once by the shop and once by me. These are new AC Delco parts. ---
**Author:** ![RobSexton](https://avatars.discourse-cdn.com/v4/letter/r/e56c9b/32.png) [@RobSexton](https://community.cartalk.com/u/RobSexton)\ **Post date:** [April 8, 2018, 2:27am UTC](https://community.cartalk.com/t/2003-gmc-sierra-1500-p0455/115154/6 "2018-04-08T02:27:53Z")
New gas cap from dealer.