So I’ve searched and read all of the threads covering the “not shifting out of park” concerns but my issue seems to be different.

When getting ready to go on a fishing trip, the low battery light came on; I replaced the alternator with a Carquest brand alternator as I could not find a GM/AcDelco part locally. We then pulled to a flat part of the road to check the oil before starting the long drive to the beach. While checking the oil, the aftermarket radio froze. While tapping on the radio, the radio pushed into the dash little bit. I seriously doubt any of this is connected to the shift interlock but trying to give a whole picture here.

So we took apart the center console to use the manual method of depressing shift interlock to get the H2 out of park and back on the road.

Once back home, in an attempt to repair the truck not shifting out of park unless the shift interlock is manually depressed, I replaced the shift interlock solenoid and the brake safety switch. Neither of these parts fixed the issue. The wires all seem to be in good condition. I do not see a BTSI fuse under the hood or on the driver side of the dash. ALL fuses test out as working properly. Using a PowerProbe, I found that one of the terminals on the shift interlock wiring harness provides power once the brake pedal is pressed as it should. But the solenoid will not release the little tab that holds the shifter from releasing from park.

I can’t seem to find a wiring diagram for our 2008 H2. Also, I can’t find if the neutral safety start switch is located on the exterior of the transmission or it is internal to the transmission. I imagine this is related…my driveway is extremely steep and the E-brake never seems to be able to hold the truck still so when we put it in park, the truck rolls back slight in park putting pressure on the transmission.

What could I be missing? Any help would be greatly appreciated. Under hood fuse panel photo below.

 

Updating here since I can’t find the section to edit my signature and I think this info might be needed.

2008 Hummer H2 SUV
130k miles
Black on black
No engine mods

 

if power is getting to the solenoid then you need to verify the ground to it. check its grounding point terminal to the chassis for corrosion. i am not positive if it's location is behind the e-brake kick panel on an 08.

 

Must emphasize I've no direct experience with the shift solenoid, so not 100% sure, however it looks like later model years are wired very differently.

Below is the 04 wiring:-


This is the wiring I found for an 08:-

It may explain why there is no BTSI fuse as the BCM now controls the solenoid, but again I'm not 100% confident about this.

It also supports @bronxteck comments.

 

That is a great point! Thank you! I’ll check that again. I did see that I had ground via the Power Probe but I did have one pin that gave me bright power nor ground whether the key was on or the brake was applied.

 

That is a huge help. My apologies for the inconvenience but you don’t happen to have access to which pin on the connector is power and which is ground, do you?

 

that is the diagram of the colors. light green with black (L-GN\BK) is positive and black (BK) is negative. you need to find where ground point G208 is and check it.

 

More wiring info:-

Another consideration could possibly be serial communications related since you mentioned your aftermarket radio. Your radio may be connected to the low-speed serial bus going directly to the BCM, if it's corrupting the serial bus this could affect BCM operations, so it might be worth unplugging the radio completely just to check.

 

10/4. I could swear that I had a pink wire. I’ll double check.

 

Agreed. I completely gutted the radio and steering wheel adapter last week, as I wanted to start fresh for the new one. Still no change. Thank you for the diagram!