I recently replaced a transmission in a 2003 Trailblazer. 4.2L 4x2. The job went off with no real problems, plenty of the proper tools and know how. After installation I fired up the truck and got the fluid levels right and went to test it out while still on the stands... The shifter is stuck in park now. I have tail lights, verified all the fuses are good. I wasn't hearing a "click" from the BTSI solenoid beneath the shifter, so I took apart the center console and verified that the solenoid was not clicking. I have power going to it from the red wire, but the light green/black stripe wire that should get power when applying the brake is not getting any power. I supplied this terminal with 12v and got the solenoid to click, verifying that the shifter solenoid is indeed working. I tested voltage on all the fuses and get a 12v reading from all the fuses, except the BTSI fuse. The steering wheel won't lock in park with the ignition off either, so it led me to test the ignition switch input wires(red & red/white stripe) and the output wires(pink and white) and all four tested out to 12v. Not sure what's going on here! Was thinking that maybe I wiggled a ground wire loose when freeing the transmission from the motor during the uninstall, but I should see 12v at the BTSI fuse correct? Any help or guidance would be greatly appreciated! Thanks in advance!

 

So I just want to make sure I understand your post clearly. The BTSI fuse in the UBEC is only hot when the ignition is in the Run/Start position. Was they igniton in that position when you checked that fuse? If it was, check the "BACK UP" fuse in the UBEC (fuse 27; 15a). If the fuse is good, and with the key in the "RUN" position, check it for battery voltage. If that is good, move to your Park Neutral (PNP) switch (mounted on left side of tranny and back probe the light green wire (pin "B") on connector 2 (the upper darker gray connector) for voltage (ignition in "RUN"). Let's see where that takes us.

 

The BTSI fuse is never hot, regardless of key position, running or not. The BACKUP fuse reads 12v, as does the IGN0 fuse under the backseat. Going out to check the PNP now!

 

When I say hot, I mean voltage going thru it.

 

OK, 10-4! I apologize, yes the BTSI fuse does have voltage running through it, but it's so low I had to set my multimeter to mV to detect it... It reads around 9 to 10mV... As for the light green wire running into the top plug of the transmission, PNP I believe you called it, it does not read any voltage with the key in the run position...

 

Hold on, trying to upload an image but my tablet is giving me grief.

 

Just to make sure we are on the same sheet of music, the attached image is the PNP switch mounted on the lower left of your tranny. Unplug that same connecter (C2) and probe the harness side of the pink wire (cavity "C"). Key in run (KOEO). Voltage comes from the UBEC, through the pink wire into the PNP switch and then out the PNP switch thru that light green wire back up to the BTSI fuse (yes, back in the UBEC) then out of th BTSI fuse where it splits off to provide voltage to both the Park Lock Solenoid and the A/T Lock Control Solenoid (via the Stop Lamp switch.

Since one of the solenoids is open with key on and the other solenoid is closed, I'm trying to determine the circuit design which may be why you aren't seeing voltage. But you should definitely see it oon the pink wire.

 

Without even going out to the garage I can tell you from having already doing it a cpl times that in the smaller connecter on the left side of the transmission, all 4 wires are hot when probed, key in run position... And on the bigger grey connector right above it, the only 2 wires in that connector that are hot, are the 2 pink wires... There are 2 pink wires but one is a bigger gauge than the other and they are both hot with key in run position

 

Ok. So could be by design the voltage is being pulled to ground which is I believe might be by design and would be why you don't see voltage. So let's take that element out. Unplug the Stop Lamp Switch and the plug at the Shift lever for the solenoids. Check the harness side of the shift lever plug. Nothing should be pulled to ground then. Probe that LT GRN/BLK wire on the harness side of the solenoid plug to see if you get voltage. Also probe the same color wire on the harness side of the Stop Lamp switch for voltage. You should see voltage on both wires. At least then we will know for sure that everything is good up to those two plugs.

But have both plugs unplugged at the same time (Stop Lamp Switch and Shift Lever plug).

 

See attached.