This started after trying to determine why the battery would sometimes go down overnight. Had pulled the fuses and relays one at a time and replaced looking for a short. After this it now only turns over but doesn't start up. I did notice that the steering column doesn't lock any longer. Also by accident inserted the key for my 2006 Silverado and it turned the ignition switch. Could this be a problem with the Passlock? The fuel pump comes on when the ignition is turned on for about 3 seconds and goes off.
2003 Sierra with 4.3L engine turns over but doesn't start. on 2003 GMC Sierra 1500
If your passlock is the problem the security light will stay solid or flash. Sounds like something is not plugged in correctly or possible fuse. Make sure the shifter is all the way in park.
passlock issue try a relearn procedure. try www.alldatadiy.com