GM TEHCM

GM TEHCM (Transmission Electro-Hydraulic Control Module) — Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired (GM TEHCM) and the problem is still happening.
Important: Please do not open/disassemble the module or probe pins from the front of the connector.

• Step 1: Confirm the exact symptom and pull codes first

  • Scan ALL modules and save the full code list with freeze-frame.

  • Note if it is no move/no shift, limp mode, harsh shifts, stuck in one gear, PRNDL issues, or no communication.

• Step 2: Battery and charging health

  • Low voltage can cause TEHCM resets and false shift/pressure codes.

  • Confirm battery condition is good and charging voltage is stable while running.

• Step 3: Verify transmission fluid level and condition

  • Use the OEM procedure for checking level (temp-sensitive on many GM units).

  • Low/burnt/contaminated fluid can trigger pressure, slip, and ratio errors that mimic a TEHCM fault.

• Step 4: Inspect the case connector and harness (very common)

  • Check for bent pins, corrosion, fluid intrusion, damaged seal, or a connector not fully seated/locked.

  • Inspect the harness routing near the transmission for rubbing, oil saturation, or broken wires.

• Step 5: Confirm power and ground under load

  • Check the related fuses with a test light (not visual only).

  • If intermittent, wiggle-test the harness while monitoring scan data and voltage drop on grounds.

• Step 6: Check for internal transmission/hydraulic causes

  • Shift solenoids, pressure control solenoid, valve body wear, or internal leaks can set the same codes as a bad TEHCM.

  • If you have gear ratio or pressure performance codes, prioritize hydraulic/mechanical diagnosis.

• Step 7: Verify programming/adaptations after install

  • If the unit was replaced or programming was performed, it may require correct calibration, setup, and adaptive relearn with a capable scan tool.

• Step 8: Network/communication complaints

  • If you have U-codes/no comm, inspect CAN wiring, grounds, and splice points for corrosion or damage.

  • Check for water intrusion at connectors and underbody harness points.