Originally Posted by lifted gmc
To reset it back to the first factory start
If your ECM has not been re-flashed with a new program. Simple to do, turn the ignition keys to the run position "engine not running" and pull the ECM fuse out from the fuse block for 20 seconds then place it back in. You should hear the fuel pump energize the fuel line, then turn the ignition key to the off position for 10 seconds and turn on for 30 seconds and turn off again for 5 seconds and then start the engine with a 10 second pause. This will reset your ECM to default and erase DTC history. The engine may stall, but let it. DON"T TOUCH ANYTHING, just restart the engine and let idle for 3 min then go for test drive. The ECM is just relearning all the sensors in the drive train. Good luck and the transmission my shift hard at first but will reset it self also after test drive. Any issues will show up as a MIL light will come on to indicate and the Sierra will need to be scanned for the DTC codes, Auto Zone scan free of charge. Good luck and keep us posted.
Why do you need to reset your ECM????