Engine Light comes on and off. Blinks!

SOURCE: 2002 GMC 2500HD 8.1L

Sounds like the cam positioning sensor. I have a 2002 GMC 2500HD 8.1L and this happened to me. Hope this helps.

SOURCE: The "tighten fuel cap" message

It's the gas cap sensor. Or you are getting a vaccuum leak somewhere.

SOURCE: GMC envoy after I filled gas tank the low fuel

You will need to replace the fuel level sensor which is in the fuel tank.They have a lot of problems because the metal fingers on the sensor wear off and gives you the incorrect readings.This will also cause the check engine light to come on.You will probably have a level sensor code.This will be a lot easier if the fuel level is down to about a quarter tank or less.Also you should be able to get just the level sensor and not have to get the complete fuel pump module.Good luck.

SOURCE: 2007 GMC Envoy - Gas gauge showing empty and check engine light

This is a safety feature that the vehicle brings. You need to reset the E.C.U on dealership or it will keep doing it to you. It was probably caused by one single time that you did not closed the fuel cap correctly. Good luck

SOURCE: 2003 GMC Sierra 5.3L (has

CODE PO120 - TP SENSOR 1 SIGNAL RANGE PERFORMANCE. CODE P1516 - TAC MODULE THROTTLE ACTUATOR POSITION PERFORMANCE. CODE P2135 - THROTTLE POSITION SENSOR 1 - 2 CORRELATION ERROR. THIS IS A DEALERSHIP FIX YOU HAVE PROBLEMS OR FAULTS IN THE THROTTLE POSITION SENSOR.