I have 2003 v6 silverado recently converted to a v8 5.3. I'm getting several trouble codes, can someone tell me how to fix them. 1.) PO455- Evaporating Emission System Leak Detected (i have a feeling its the gas cap) 2.) PO480 Cooling fan relay 1 control circuit - PO481 same as PO480 but relay 2. I have cleared the codes but they still come on. Also tried disconnecting the battery too! Everything works fine the check engine light is starting to get to me.

Who did you get your PCM from???? Did you do the swap yourself?

PM me for more info....

Are you using elec fans or mechanical?? Just something we need to know about when the swap was done

The fans are mechanical.

well there is the answer to p0480 and p0481, you have a pcm that was once made for use with electric fans and now since there are none it will set the DTC's.

The guy said he could not make the electric fans work, so he put a mechanical fan. He has had this problem with other trucks when a v6 was swaped for a v8 with electric fans. I forgot to mention this.