Engine control module (ECM / PCM) codes

How its codes differ

• P0606 and P0607 come from the computer checking its own processor and memory, or finding it is not programmed or programmed wrongly. GM service information has the battery, cables, power feeds and grounds checked, and the module reprogrammed, before the module itself is replaced.
• P061B is an internal check that the computer's own torque calculation makes sense. In the bulletins we found, Mazda and Ford fix it with new software rather than a new computer.
• U0100 is stored by other modules that stopped hearing from the engine computer. Damaged network wiring, power, ground or a wake-up circuit is more often the cause than the computer itself, so check those first.
• A low battery or a poor ground can make a healthy computer, or another module, set these codes. GM bulletins describe the brake module setting P0606 from low voltage on 2019 to 2026 trucks.

Codes

• P0606

  A control module found a fault in its own processor or programming

  Severity: Inspect soon

• P0607

  A control module failed one of its internal performance checks

  Severity: Inspect soon

• P061B

  Engine computer’s internal torque calculation check failed

  Severity: Inspect soon

• U0100

  Lost communication with the engine or powertrain computer

  Severity: Inspect soon

Signs it's failing

• Check engine light with P0606, P0607 or P061B
• U0100 stored in other modules
• Stalling, no start, or the engine shutting off while driving
• Harsh shifting or reduced power on vehicles where the computer also controls the transmission

How to test it

1. Read and note every stored code in all modules with a scan tool, not just the engine computer. Another module may have stored the code, and other sensor codes usually point to the real fault. (Low risk)

2. Have the battery and charging system tested; many parts stores do this free. Check that the battery cables are clean and tight. (Low risk)

3. Ask a dealer whether your VIN has a software update, bulletin or recall for the code before agreeing to a new computer. Several makers fix P0606, P0607, P061B and U0100 with software. (Low risk)

4. Testing the computer's power, ground and network circuits, reprogramming it and replacing it are jobs for a shop with the maker's programming tools. (Best left to a shop)

   Warning: A replacement engine computer has to be programmed to the vehicle and the anti-theft system relearned, or the engine may not start. Connecting test leads to the wrong terminals can damage the module.

After the repair

• After a new computer is fitted, confirm the shop completed programming, the anti-theft learn and the relearn procedures the maker calls for, such as the crankshaft variation learn and throttle idle learn on GM.
• Have history codes cleared in every module once the repair is done, so old codes do not mislead later diagnosis.
• Drive normally over several days with both city and highway driving so the readiness monitors can complete; replacing or reprogramming the computer resets them to not ready, which fails an emissions test.