Lbz starter cranks in on position

[javithewrench]

My 07 classic started cranking when the key was turned to the run position.I’ve looked and haven’t found any solid answers anywhere but this fixed my truck. In the under hood fuse box I noticed a relay (#5 ignition) was facing the wrong way as all the others looked backwards when looking at them from the drivers fender. I checked that relay and the diode was popped, so I installed a new one the correct way and she’s back to normal. I looked online and noticed lots of relays are backwards?? I’m the original owner and have never messed with these relays so I’m guessing it’s been that way from the factory. Hope this helps
Notice the relay with the writing installed backwards, these are random pics I found online

 

[dndj]

Those rectangular relays (horn, DRL, A/C compressor, etc) function fine when plugged in either direction since the flyback/snubber component in parallel with the relay coil is likely just a resistor, not a diode. My GM FSM schematic shows a snubber resistor, although I will admit I haven't torn one apart to look. Pins 85-86 are the SPST switched circuit and 30-87 is the control coil and these work when the relay is plugged in either orientation. If a snubber diode was used, orientation would obviously matter, but the wrong direction would lead to a no-start since the relay coil circuit in the ECM would connect the diode from +12v forward biased to ground, keeping the coil from energizing until the diode or ECM control circuit burned up. If the diode blew first, in theory the relay would work just fine after that, but without flyback voltage spike protection when the relay shuts off.

The switched contacts 85-86 were probably burned together in your starter relay causing your truck to attempt to start when key was placed in the ON position.

 

[javithewrench]

That’s interesting, I guess that’s why you can plug them in either way. What I don’t understand is why my truck starts normally now, the relay I replaced was #5 ignition not the starter relay. Thanks for the info

 

[dndj]

Hmm ok I misunderstood which one you replaced, I was assuming one of the rectangular relays. If you're talking about one of the 3 larger square body relays, the one marked 5* in the last black and white picture? That is labeled EDU on my truck. This relay runs the FICM and energized by the ECM presumably when the key is in on or start positions.

Not sure why your truck would crank in the on position, I thought the ECM would only do that if it saw +12v on the CRANK circuit which is only connected to the start position on the key.

 

[LBZ]

I’m gonna guess it was coincidence. I feel like this will come back and a new ignition switch is going to be in your future. Or possibly a new start relay.

 

[javithewrench]

I’m starting to think maybe the contacts in that relay #5 were stuck closed. Now that I know the relay doesn’t have a diode, I’m really confused. She has been starting up fine. That’s for the help guys!

 

[dndj]

I'm kind of thinking along the lines of LBZ's comment. Your starter relay contacts may have been stuck together, fiddling around in the fusebox while you were changing 5* may have been just enough to knock it loose. Problem may come back. Good to have one of the rectangular relays as a spare in your glovebox anyway since there are 7 of them used in the underhood fusebox.