1996 Tahoe 5.7 No Crank Ignition Switch

[Glin60]

Background:
I have a no crank condition on a new to me 1996 Tahoe 2 door that I’ve run the GM Service Manual troubleshooting tree on, researched the forums, and I'm looking for some ideas on where else to check. The vehicle itself has 350k miles, but seems mostly original for better or worse (aside from some old audio equipment wiring that I've removed). In the month I’ve had it so far, the truck has been cranking, starting, and running just fine. Last weekend, I replaced the radiator, water pump, T-stat, heater core, belt, and tensioner, fired it back up and ran for about 15 minutes to bleed the cooling system. Shut down and went to re-start a few minutes later and it would not crank with the ignition switch. It does crank, start and run when jumpered at the solenoid/relay. These systems have been consistent throughout and persist despite the troubleshooting below.

Symptoms:
Turn the key to run and the dashboard lights come on. Fuel pump primes. Move the key to start and there is no crank. On the first attempt, I’ll get what sounds like an additional fuel pump prime, and what sounds like a click around the fuel spider on top of the manifold, but nothing following that, or on subsequent cranking attempts until I recycle the sequence again. However, when jumped directly at the solenoid and at the starter relay in the underhood fuse center, the starter cranks and the engine starts. This has led me to troubleshooting the control side of the starter circuit.

What I’ve done so far:
Normally, something like this happening shortly after doing work on a car, makes me go straight for what was disturbed during the course of the previous job. In this case, I didn’t disturb much of the starting system doing the cooling work, but moved some harnesses around at various points. So I started with the following actions:

• Battery charged to ~12.4V
• Replaced positive battery terminal (preventative, looked terrible)
• Replaced negative battery terminal/ground cable (2 AWG)
• Inspected/cleaned grounds G101, G102, and G105 (relevant to the start control circuit)
• The ground wire terminating at G105 displayed chafing and exposed wires (photo below)

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• I spliced in new matching 10 AWG with a crimp-style butt connector and heat shrink, which subsequently checked good for continuity and resistance.
• Issue persists
• Swapped relays with A/C relay, no change

Next I ran the troubleshooting tree in the 1996 GM C/K Service Manual (I bought the paper copy before I realized you guys are awesome and have PDFs available to DL as a sticky, but actually like paper copies for note taking and ease of flipping between multiple sections... Have I mentioned how impressed I am with this forum yet?):

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Notes from the troubleshooting tree:

• I’m getting 12v from the battery to the relay
• I’ve got continuity from the relay to the ground
• I’m not getting 12v from the ignition switch circuit to the relay when switch in start
• I’m not getting 12v at the Park/Neutral Position Switch yellow wire when switch in start
• I’m not getting 12v at the instrument panel fuse box #8 cranking fuse when switch in start
• I’m not getting 12v at the ignition switch yellow wire (signal from the ignition switch) when switch in start
• I AM getting 12v at the red wire (242 in the manual) running to the ignition switch.
• The troubleshooting tree indicates the ignition switch should be replaced based on these observations, which made sense to me. However, I replaced the switch with a new one from NAPA and the symptoms remain unchanged. (Caveat: following switch replacement, the key/door buzzer now buzzes constantly for some reason, whereas it never made a sound before. The ignition switch behavior did not change regardless if I had the sensor on the tumbler connected or not)

Where to go next:
Looking at the schematic there’s not really much else obvious to explore, but are there other things related to this circuit not on the schematic that could influence its behavior? I’m tempted to start digging into other splices (elsewhere in the ground distribution or pertaining to the ignition switch, but want to make sure I’m not chasing ghosts and unintentionally creating other problems along the way. I'm also not above taking the switch back to NAPA and asking for a new one, but I'm not sure that's the problem either. Moreover, I’m not a professional, especially with wiring, so definitely not afraid of constructive criticism from those with more experience. Searching the forum so far has yielded some awesome posts and dialog addressing many similar problems and solutions, but I didn’t see any this drawn out. Any ideas?

Thanks in advance for any thoughts or insight!

 

[Cadillacmak]

• I’m not getting 12v from the ignition switch circuit to the relay when switch in start

Park, neutral safety switch? Try moving the shifter around while cranking, if that works it needs adjusted or replaced.

 

[movietvet]

Yes, like @Cadillacmak said, try starting in neutral and other positions. Everything I read from you says "ignition switch". Power in but not out. Possible bad new part.

 

[Schurkey]

• Battery charged to ~12.4V

A fully-charged battery should show 12.6--12.8 volts. Yours is still semi-discharged.

But that's not the real problem.

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• I spliced in new matching 10 AWG with a crimp-style butt connector and heat shrink, which subsequently checked good for continuity and resistance.

"Continuity and resistance" are poor tests on heavier-gauge, multi-strand wiring. You'd be MUCH better-off to be doing Voltage Drop testing on such wires. Voltage Drop testing is functionally similar to checking resistance with an ohmmeter, but it does so with the circuit under load, not static. A single strand of heavy-gauge wire in a multi-strand cable might show acceptable resistance and continuity, yet the cable could be incapable of carrying it's intended load.

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• I’m not getting 12v at the Park/Neutral Position Switch yellow wire when switch in start
• I’m not getting 12v at the instrument panel fuse box #8 cranking fuse when switch in start
• I’m not getting 12v at the ignition switch yellow wire (signal from the ignition switch) when switch in start
• I AM getting 12v at the red wire (242 in the manual) running to the ignition switch.
• The troubleshooting tree indicates the ignition switch should be replaced based on these observations, which made sense to me. However, I replaced the switch with a new one from NAPA and the symptoms remain unchanged. (Caveat: following switch replacement, the key/door buzzer now buzzes constantly for some reason, whereas it never made a sound before. The ignition switch behavior did not change regardless if I had the sensor on the tumbler connected or not)

You have power into the ignition switch. You don't have power coming out of the ignition switch when in the "Start" position.

Switch is misadjusted, defective, or the wrong part for the application.

Disconnect switch (perhaps remove entirely) and test with ohmmeter between power input terminal where Red 242 connects, and power output terminal Yellow 5 connects, when switch is manually turned to "Start".

 

[GoToGuy]

If your not getting power out of the start switch when cycled that's your first problem. As said above. No power out of start switch , further downstream testing is a waste of time till it's fixed.. what manual are you using? It doesn't look like GM FSM.

 

[Glin60]

Thanks all for the quick responses! A few follow ups:

You have power into the ignition switch. You don't have power coming out of the ignition switch when in the "Start" position.

Switch is misadjusted, defective, or the wrong part for the application.

Disconnect switch (perhaps remove entirely) and test with ohmmeter between power input terminal where Red 242 connects, and power output terminal Yellow 5 connects, when switch is manually turned to "Start".

Concur, based on this, I took your idea to check for continuity of these two terminals and turned the key in the ignition to crank. Did not show continuity. However, I removed the switch entirely and used a screwdriver to manually test the function of the switch. When driven counterclockwise to the 5 o'clock position, it has continuity. This made me wonder how far the key was driving the spline, and if it was getting to the required position to crank.

With the ignition switch removed from the rest of the ignition lock housing, I can see the orientation of the white plastic spline that engages with the electrical side of the ignition switch. When I turn the key fully to crank, I could see that the orientation of the spline only rotated to the 7 o'clock position, short of the 5 o'clock position the switch was looking for. Photo Below:

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Follow on questions: Does it seem like the switch should be rotating further into the crank sequence? The fact that the key-activated switch at max rotation does not match or attain the position required to crank seems to indicate something is not right. To be clear the exact symptom and key feel was occurring with the old switch as well. Is there a mechanical adjustment available for the ignition key on these models? Would think an adjustment would get us back to where we need to be.

UPDATE: With the harness connected, but the switch end not installed, I'm able to start the vehicle by manually actuating the switch input with a flat-head screwdriver. That makes me believe the electrical side of the system is good, but the mechanical interaction between ignition lock cylinder and the switch itself is the issue. Given that it displayed identical symptoms with both switches, it leads me to believe the root cause is on the ignition lock cylinder and/or housing side of things. Any adjustments there to restore full deflection?

Additional background, I believe the cylinder has been replaced at some point, when I bought the truck it didn't come with keys and the GM-made keys based on the VIN didn't turn in the ignition, (but did on the doors). Had a locksmith re-key the cylinder to match the GM-made VIN specific keys and all was golden. He mentioned the cylinder had some wear, but nothing too bad. Could something in the ignition lock cylinder be preventing the key from turning fully to crank?

Thoughts?

 

[Glin60]

If your not getting power out of the start switch when cycled that's your first problem. As said above. No power out of start switch , further downstream testing is a waste of time till it's fixed.. what manual are you using? It doesn't look like GM FSM.

Indeed the 1996 GM C/K Truck FSM. 2 large books for this year. The GM FSMs are a stickied at the top of this forum as well. If there's a different one I should be using, please let me know.

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[GoToGuy]

Got it, great choice. In the first book CK-1 is the starter troubleshooting/ diagnostic. Chapter 6 Engine, section 6D cranking system.
The CK-2 , chapter 8 deep dive electric diagnostic.
Seems you found it, so is the plastic pin clocked in wrong position, is your tumbler not rotating enough, is the rod damaged, ?

 

[Glin60]

Got it, great choice. In the first book CK-1 is the starter troubleshooting/ diagnostic. Chapter 6 Engine, section 6D cranking system.
The CK-2 , chapter 8 deep dive electric diagnostic.
Seems you found it, so is the plastic pin clocked in wrong position, is your tumbler not rotating enough, is the rod damaged, ?

Scouring said manuals, forums, and YouTube now to see if there's a way to adjust any of those items. Turning the key had always felt more or less normal, but it did seem that maybe it seemed to crank a bit sooner than I would normally expect, but I've not have the truck long enough to know what normal should feel like, and don't really have much experience with GMT400s in the past to compare this one to.

With as much of the column I already have apart, I may pull the tumbler out to inspect it, and see if there's any way to adjust the relationship between how far the key turns and how far the plastic pin rotates. Not a ton of experience in messing with these in the past, but it looks just as simple as the lock cylinder, housing and switch. I'm vaguely aware that the older models have rods that you can adjust, but do these have something similar, or is it more direct?

 

[GoToGuy]

You have service manual, steering column breakdown, I'd start there.