Garrett Kuehner

I found this through a search. So the TCCM grounds a positive voltage from the VCM; the question is how much voltage? The circuit indicates a resistor between ignition voltage and the outlet from the VCM, so it could be anything between 0<x<12V. I really don’t want to burn up the TCCM. Odd request, but is anybody willing to measure this signal on their truck? I believe The VCM should only output a voltage on this circuit when all the conditions to shift into 4lo are met. So you would need to put it in neutral and measure the output voltage (at C4-23 for a 4.3, C2-16 for all other engines) BEFORE selecting and shifting into 4lo. Once 4lo is engaged and the circuit is grounded, you may not get an accurate reading. thanks, garrett

Anybody? Or have I stumped everyone? the only other option I can envision is the TCCM is skimming serial data through PCM C1-53, which is connected to the OBD2 port. thanks again, -Garrett

All, I finally upgraded the driveline on my Grand Wagoneer to an LM7 swap from a 2000 Tahoe (same as Silverado), to include the 5.3, the 4L60E, and the NP263 electronic transfer case. Initially I conducted the swap with the OEM harness, ECU, and TCCM. The t-case shifted as desired into all gears/ranges. I recently upgraded the OEM harness/ecu to a Holley Terminator X, which eliminated the communication to the TCCM from the PCM (grey/black .35 wire, PCM C2-16 labeled “4wd signal low”). Now the t-case will only shift between 2hi and 4hi. Does anybody understand the logic from the PCM to the TCCM? The PCM must be communicating the transmission status (particularly neutral) to shift into low range - does anybody know how? Is this as simple as connecting a ground, 12V, or 5V signal, or is it as complicated as a string of serial data between the two modules? thanks for any insight you can provide.