Engine light I have a 2004 gmc savana and check engine light came one. Mileage 79875 and have had no problems so far. What could be the problem?

The check engine light notifies you of any faults within your emissions systems. Many parts and systems within your vehicle are emissions related but a sensor must notice the fault the first and then send a message to your ECM(electronic control module) otherwise known as your computer. this will trip the check engine light. If you have noticed no attributes related to your emissions system such as rough or uneven idle, sluggish accelleration or missing throughout the driving or idling range (slight loss of power) then there is the probability that you did not put the gas cap on tight enough. Always make sure you turn your cap until you it clicks a number of times. After doing this and keeping it in mind you can try to reset the computer by removing the negative battery cable for a while (3 minutes mimimum) and reattaching. If the light is now gone and does not reappear you have found the problem. If the light is still on immediately after reattaching the battery then your computers memory has not been cleared. If the light comes back on then you can try to pull the codes from your computer if it is OBD1. You can tell this by looking at the diagnostic connector under the dash right around where the drivers left knee would be. If this connector has 2 slots with metal connectors and the far right either at top or bottom you should be able to get the stored fault codes. If there is only one or no metal tabs in two adjacent slots of the connector then your system is OBD2 which means you would need to have the codes read with a scan tool. Most mechanics should do this for around $40. If it is more call someone else.

Renove the rock shield from arround the gas filler. (they zip tied it on the bottom You may find the copper groung wire corroded to the pipe allowing a leak (great engineering) if possible remove and braze pipe >$150.00 , replace ground strap and this time either **** the shield or this time put the zip tie up top so the shield will not retain water,