2003 2500HD 6.0 4 Wheel Drive P1518 code - thru Headlights

bobm396 · October 1, 2014

2003 2500 HD plow Truck has 175,000 miles. Blew head gasket 2 weeks ago, sent to garage for repair and all was good. 3 days and 35 miles later I take it for a ride and P1518 – P0758 – P1516-P0120 “Reduced Engine power”. I go on the web and read for 2 days straight. To date I have cleaned / replace a lot of grounds. (No ground strap on back of right side head) Perhaps garage failed to install after the head job? 2 sets of jumper cables ( temp grounds) I don’t think grounds are the issue

I replace the throttle sensor on the throttle body but did not replace the plug. I did do the pull test on the wire. I do not think there is a broken wire.

Heres the weird thing !!

If I clear the errors and disconnect the battery I can start the truck and it seems normal until I turn on the high beam head lights. The truck will shut off at that point. If I repeat the process start the truck and unplug the head lamp, the truck will shut off. If I Repeat the process and pull the head light fuse out of the holder the truck will shut off.

If I install the head light fuse with the ignition on I can hear all the electrical on the engine activating.

It seems like the engine accessories are now being powered thru the head light system.

Anyone have a thought or can maybe send me in the right direction

Thanks bob

gmtech4 · October 1, 2014

Sounds like it's the garages problem ,,, not yours , take it back , you have a year warranty on repairs , all shops do

bobm396 · October 2, 2014

Thanks for the information

bobm396 · October 2, 2014

Rob, My thoughts also. However you know the garage is going to say they worked on the heads and this has nothing to do with that repair. Then it’s going to turn into a debate on who pays for what. I thought I would take a crack at it first ...however after 3 nights of getting nowhere I might be changing my mind soon ...Thanks

gmtech4 · October 2, 2014

Rob, My thoughts also. However you know the garage is going to say they worked on the heads and this has nothing to do with that repair. Then it’s going to turn into a debate on who pays for what. I thought I would take a crack at it first ...however after 3 nights of getting nowhere I might be changing my mind soon ...Thanks

you need a schematic bad to do this

buy alldata $27/yr

maybe you can self diagnose it from the schematics