02 Sierra 4.8 will not start when key turned; guages, lights, radio come on...

[02SierraTucson]

I have looked through the forums and found some posts like mine, but not exactly.

 

About 3-4 years ago my truck started to not start with the key turned, everything else wo`uld come on: radio, fuel pump, gauges, lights, etc. I would swap the start and ignition relays, clean the relay posts and sockets, tap them together, and the truck would start. It would do this intermittently, and then about two years ago it stopped.

 

Fast forward to a few days ago, It started again. The only change in the last couple years is that my ignition lock cylinder has gotten to the point that I can pull the key out with the truck running. I thought this might me it, but it is a mechanical part, not electrical. I'll be changing it anyway. I thought it was the cold as it would not start after work yesterday, but it started fine this morning.

 

A few things I tried, I put a jumper across terminals 30 and 87 on the relay socket and the started turns over. I have checked the battery cables and they are clean and secure. I have not tried starting with the gear select in neutral.

 

Before I start throwing parts at it I wanted to hit up the hive mind first. I was thinking start relay in the column, replacing the start and ignition relays in the engine compartment, and obviously the cylinder.

 

When I turn the key, I can hear a relay in the engine fuse box clicking, could it still be the ignition relay?

 

Any help would be appreciated, this is my only vehicle right now. Thank you all. 

[richard wysong]

Welcome to the forum! My money is on either a bad neutral switch or the wiring to that switch. Before you fire the parts cannon get a wiring diagram and a DVOM meter and see where the fault is. The factory service manual or Alldata will have the diagram and the diagnostic tree to find the problem, Haynes manuals may not have this info

Edited February 4, 2023 by richard wysong

[Scott Tucker]

Do you have a wire harness or access to wireless harness diagram,, I would check for 12 votes on the starter relay, There should be 2 12 volt Circuits One is a 12 volt all the time and the other 12 out when you turn the ingntion switch to start,, I'll be glad to help you with it I'm old and type slow But I am Chevrolet certified in 1988 ASE mastertech by 1990 , But I'll try to walk you through it

 

[richard wysong]

Welcome Scott! It sounds like you may be a great asset to the Forum. 

[02SierraTucson]

Scott, thank you for the info. I have a wiring diagram in the maintenance manual I have. I will check the voltages.

 

What would cause those voltages to be intermittnet? the truck does start, just intermittently does not.