I have a no start issue on my 2003 GMC Sierra that I'm trying to figure out.

It just randomly decided to not start.

The symptoms are:
The starter relay clicks when you turn the key and then all power items go dead until you turn the key off and on again.

Replaced/Tested
Battery - brand new this week - verified voltage at 12-12.5v with the key on.
Starter relay - swapped with the relay next to it.
Try my other key.

The weird thing is the truck fires up and runs perfect if I clear the codes (I'll get those when I get home). It'll start/run normally for a day or 2 - then it'll start this crap all over again. It's like the pcm goes stupid and needs scanner
communication to come back alive.

Any ideas?

 

What codes are you getting? Have you checked the grounds?

 

Sounds like a bad ground or connection somewhere. Check that both battery posts are tight, the ground against the drivers side of the block, the power cable to the starter. Also check for corrosion.

 

I'll post them up when I get home.

 

I thought that too - but clearing the codes completely fixes it. I.E. the truck runs/starts/drives perfect after the codes were cleared. I'll still double check them.

 

But honestly there are no codes or actions of the PCM to disable the starter like that. If it were some sort of security system problem, you wouldn't hear the starter solenoid clicking. It would just shut down the entire system until you released the key from the start position. All the PCM does is applies a small amount of current to the starter solenoid to activate the solenoid. The clicking you're hearing is the solenoid not receiving enough power from the battery to activate the starter. There is no break in the connection from the battery in the starter for the PCM to sever.

 

Verify the relay clicks. If it does click pull the relay out and use a wire jump terminal 30 to terminal 87 starter should crank engine. If it does not can you hear the starter solenoid click it will be a heavy mechanical click. If you hear heavy click of the solenoid but the starter does not spin the engine probably have a bad starter but check all grounds.

All the pcm does is supply ground to the starter relay to close the contacts and then sends 12 to engage the starter solenoid.

check all block grounds they are at the drivers side lower side of block, back of head by the manifold on the drivers and passenger side. nearest the coolant block off plates on the heads.

 

We've had this happen so several of our vehicles. Usually a bad starter or a bad ground, which has already been suggested. Also, I can confirm that the factory vehicle immobilizer disables the fuel rails, not the starter, so the security system is not the culprit

 

Well it appears that clearing the codes must have been a coincidence. It didn't fix it tonight - here was the history:
[TCM] U1000 - Class 2 Communication Malfunction (History) (Immature)
[TCM] U1255 - Class 2 Communication Malfunction (History) (Immature)
[Brake] C0281 - Brake Switch Circuit (History)
[Brake] C0222 - RF Wheel Speed Signal Missing (History)
[Restraints] U1000 - Class 2 Communication Malfunction (History) (Immature)

Tonight it wouldn't start - I disconnected the ground at the battery and waited a minute and reconnected it.

The truck started and ran normally.

Maybe it'll start tomorrow maybe not - it's odd. Turn the key to on - everything is good, turn it to start and the starter relay clicks, everything loses power until the key is back to the on position. If it starts it'll continue to start unless I let it sit overnight......

Battery isn't the issue
Starter isn't the issue
starter relay isn't the issue

guess I'll be checking the grounds and powerlead when there is more light.

 

How did you test the starter? It sounds like that is the problem...that or there is corrosion in one of the battery cables that you can't see as it's hidden by the insulation