03 2500HD No Crank

[JD6105D]

I have a 2003 GMC 2500HD 4x4, 6.0 automatic. Now when I turn the key to the on position the fuel pump does not run (new Delphi fuel pump two years ago) and then when I turn the key all the way the engine does not crank at all. I installed a new ignition switch but no change. Battery and starter are fairly new as well.

 

Computer issue?

[Jsdirt]

Since 2 completely unrelated systems are not working, first place I'd be looking is the fuse box. Bet there's a blown fuse or 2. If that's the case, you'll need find out why they blew. The 2 components may get power from the same source, so that could be a place to start looking as well. Need to do some troubleshooting.

 

If the fuses are all good, leave the key on and start wiggling the harness near the underhood fuse box, for starters. Listen for the pump to kick on, or relays to start clicking. Try to start it if that happens. If that does happen, you'll need to weed through 100 wires to try and find what the problem is. A GOOD wiring diagram is a must. Problem is, all the good ones cost money ... monthly.

 

Another simple and free thing to try is to grab a similar relay from another circuit, and swap it with the one that's non-op. If it suddenly works, you've solved one problem at least.