ECM and Immobilizer Programming

[Chevrolet, Buick, Cadillac, GMC]

⚠️ Read notes on GM’s Global A Architecture, before swapping used parts.

Step 1. Attempt to start the vehicle (won’t start), then release the key to ON.
Step 2. Leave ignition in the ON position for 10 mins
Step 3. Turn ignition OFF for 5 seconds
Repeat Step 2 and Step 3 two more times.
Step 4. Turn ignition OFF and then to Crank
- IMPORTANT: The vehicle learns the Passlock Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.

Tech 2 has an option called “VTD option reset” (1998 Chevy Cavalier 2.2L)
It disables the Antitheft system.
Works best with unplugged passlock at the steering column. If to leave it plugged in, the car might not start.

Put a resistor (e.g. 2k) between passlock signal (yellow) and ground (black) wires.
- Sensor signal voltage should be lower than 5V. With 2k resistor should be around 2.3V.
- “Passlock Code” should say “Valid Code x” (x=number)
Perform 30 mins relearn.

Buy SPS Subscription.
Reprogram ECM
- Don’t forget to enter a different VIN and the very beginning, or you will loose your purchased subscription for one VIN
- Disconnect any aftermarket equipment. Sometimes need to disconnect communication wires to the other modules, having only PCM communicating with a scan tool.
Go to Vehicle Deterrent System Relearn.
- Note: Don’t go to Theft Deterrent System Reprogramming, it will not match ECM and immobilizer.
If diesel,
- perform Injector Flow Rate Programming
  - Autel ➱ Glow Plug Module ➱ Copy Flow Rate Calibration from GPM to ECM
  - Clear codes
📝 ECM Reprogramming | 2004 Chevy Trailblazer
- Tried to reprogram two different used ECMs with the same part number as the original.
  - SPS has started programming fine, but the last 10-11 seconds stopped with the Programming Error.
  - Before programming it asks to remove two fuses from the rear fuse box, but this hasn’t helped.
  - Without programming car doesn’t start.
- Probably needs a new ECM.
  - Customer declined repair, so cannot test this hypothesis.