06 trailblazer - No start, No crank - new starter, Ignition switch, starter relay

[dragginblazer]

Hello,

First of all I have spent hours researching trying to diagnose this problem. I have a 06 trailblazer I6 with approx 65k miles. For maybe the past week I have noticed the starter sounding weak. I did research and others said this was signs of the starter going out. Then one day the truck failed to crank. I immediately swapped a good known battery to rule out a weak battery. From there I started checking relays and fuses which all turned out good. Before I swapped the starter relay with an identical drive train relay the starter was clicking. Once i swapped the relays the starter stopped clicking. That is when I replaced the starter relay which also failed to actuate. I then was frustrated and replaced the starter which changed nothing. I am able to manually jump the starter over in the fuse panel so I know that circuit is working (did not crank this way before the starter swap). After that I replaced the ignition switch which also did nothing. All major electrical connections were cleaned. Transmission gear sensor is reading correctly and was cleaned. Crank sensor was recently replaced. Security light is not on. Coolant temp is reading correct. All other electrical is working on the truck. With the key in the ignition the throttle body is reading at 28% on my scanner but not sure if this is correct. I unplug the throttle body and it spikes to 100%. Engine block ground is clean. Does anyone have any suggestions on what else to try besides a new pcm? Thanks in advance

 

[The_Roadie]

Welcome! I didn't think the starter relay had a twin anywhere in the fuse panel. I thought it was square instead of rectangular, but I may be misremembering something.

In any event, when you jump the starter relay 47, are you specifically jumping the IN to the OUT terminals, so that fuse #34 is feeding a good 12V to the relay socket? Another test would be to test the relay's control pins with a voltmeter lead connected to a tiny wire wrapped around the relay blade so you can check it with the relay plugged in.

One end of the control coil is grounded by the PCM when you want to start. But make sure the other side has a solid 12V, fed from front fuse #22 *and* the PARK/NEUTRAL interlock switch on the driver's side of the transmission. Those items go out or end up with flaky wiring far more often than expensive PCMs die.

Added, the PARK/NEUTRAL interlock is on the same assembly, but a different contact, from the gear selection indicator switch.

 

[dragginblazer]

Thank you for the reply and some good info. Turns out either I'm an idiot or someones messing with me. I went to check the fuses once again and the pmc fuse was missing! Plugged in a fuse and the under hood stuff started making noises like normal and it fired right up.

P.S. and on this 06 TB there is an identical square relay for something in the drive train above the starter relay.

 

[bspurloc]

Thank you for the reply and some good info. Turns out either I'm an idiot or someones messing with me. I went to check the fuses once again and the pmc fuse was missing! Plugged in a fuse and the under hood stuff started making noises like normal and it fired right up.

P.S. and on this 06 TB there is an identical square relay for something in the drive train above the starter relay.

so now you have to backtrack to find out what actually was shot that you replaced before accidentally taking the pcm fuse out!

 

[DenaliHD66]

My starter has been sounding weak on cold starts the past few days. Starter works perfectly fine if the truck is still fairly warm, but the first morning starts are the weakest. Everything in the cluster goes to maximum voltage and there is no "bog down" and the lights don't dim or anything. Truck still turns over and starts in the same amount of regular time; it just has that weak sound to it. Pretty sure it is the original starter for my 2004.