TCC quirk

[flattopwill]

Just bought this ‘97 Silverado 1500 5.7 2wd auto and boy does it have some quirks. I’m hoping you guys can help me narrow some of these issues down.
Symptoms:
When I put the column shifter into reverse the parking lights come on. Including parking lights on front, tail lights, and dash lights.
Reverse lights do not work.
Blower fan only works on high and the torque converter will only lock up if the blower fan switch is in the off position or in the high position.
No cruise control. (This is probably due to CEL on)
The parking brake light on the dash comes on intermittently. Seems to be related to the throttle/load/vacuum(?) and not brake pressure.
Truck pulls to the right under initial brake application.

What I’ve done since buying:
Some brake work including the master cylinder, one caliper, both rear wheel cylinders, and shoes on both.
I replaced the multifunction switch.
I replaced the blower resistor and it made no difference to the blower speed capability.

I’ve inspected the brake switch and it appears to be adjusted well and properly functioning. (The tail lights work.) The BTSI doesn’t work so it stays unplugged. The parking brake is missing the cable adjuster so it’s not even hooked up.

I know this probably seems like a rambling list of problems but I was hoping you experts could help me connect the dots on some of these. Especially that TCC-blower fan connection!

 

[Nad_Yvalhosert]

Adjust your PRNDL switch. Get a scanner, go to the data stream and find "gear selection". Loosen the PRNDL switch and move it until is states P when you're in Park, OD when in OD, and 1st when... well fill in the blank.
That "should" start sorting the tail light issues. Also may get the TCC to function correctly, if the PCM "knows" you're in OD when the shifter is actually in OD.
Next, diag any light issues: possible short through the tail light circuit boards lighting other bulbs

 

[flattopwill]

Thanks, that’s helpful. I have a friend with a scanner so I’ll have him plug in and see if the PRNDL switch agrees with my shifter position. At least the gear indicator on the dash is working correctly.

 

[Nad_Yvalhosert]

And possibly reverse lights!

 

[flattopwill]

And possibly reverse lights!

Does the PRNDL switch give power to the reverse lights or does that come from a switch in the column?

 

[Nad_Yvalhosert]

Column physically moves the shifter arm on the transmission, PRNDL switch sends B+ power to reverse lights

 

[flattopwill]

My buddy’s scanner showed the PRNDL switch is working correctly. It also revealed a fault with the brake switch. I replaced it tonight and will give it a test drive in the morning to see if it fixed anything.

 

[flattopwill]

Test drove this morning. No change except now the BTSI works properly. The cruise control still doesn’t work. TCC lockup is still dependent on the blower fan being off or on hi. Still no reverse lights. I also tested to make sure that the TCC unlocks when I tap the brake pedal.

 

[flattopwill]

Ok so after replacing the tail light sub harness all my lighting issues have been resolved including the reverse lights.
The blower fan still only works on high and the fan speed selection still affects the TCC lockup. The TCC will only lock if the switch is in the off or high position.
Still no cruise control. By testing voltage readings at the plug at the CC module I can see my switch is sending the right signals however where I’m supposed to be getting 12V it’s actually only reading 10V. (Reading 12V directly at the battery). Also I tested the resistance for the ground pin to the ground at the intake an it’s reading 5ohms but my service manual says it should read less than 1ohm. I chased down the two grounds my manual says the cruise control uses. G103 at the thermostat housing and G104 on the back of the passenger side head. Both appear to be clean and tight.

Any electrical gurus that can help me?

 

[flattopwill]

Well I had a breakthrough. Posting so maybe someone in the future can use it. I discovered that cruise control, brake, and HVAC are all on the same power circuit at the dash fuse box. Power comes through the ignition switch. I tested voltage on that circuit at the dash fuse box and discovered it’s only getting 4.5v and it should be getting 12v. I happened to have a spare ignition switch laying so I plugged it in and voila the circuit is getting 12v and the fan blows on all speeds!

Unfortunately the truck is not running right now in preparation for an LQ4 swap so I can’t test the cruise control or TCC function but I bet it’s fixed.

The only electrical gremlin left is the passenger door lock switch doesn’t work. It works fine from the driver’s side but nothing from the passenger side. If you press the passenger door lock button nothing happens except the cab lights dim. If you hold it down it blows the fuse. I replaced the switch but no change. Also the remote door locks will only unlock. Will not lock. I figure these two functions are related.