Lost Communication with Transmission Control Module (TCM)
The engine control module cannot communicate with the transmission control module.
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What it means (plain English)
The engine control unit (ECU) is trying to talk to the transmission module, but it can't because of a wiring or module issue.
What the computer is actually seeing
The ECU is looking for a signal or data from the TCM and isn't receiving it within a specified time frame, usually over a few hundred milliseconds.
What a healthy reading looks like
The TCM should respond to the ECU within 200 milliseconds after a request for data or status, usually operating at 5 to 7 volts on the communication line.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check for any other codes, especially U codes related to communication. If present, address them first.
- 22. Inspect the wiring and connectors between the ECU and TCM for damage, corrosion, or loose connections.
- 33. Verify battery voltage (should read 12.6 V or more). Check ground connections as well.
- 44. Using a scan tool, check the data stream from the TCM. If it shows no response, proceed to the next step.
- 55. Test the TCM power supply. Should be receive battery voltage (around 12V) and ground properly. If not, address power issues.
- 66. If the TCM is not responding to power correctly, you may need to replace the TCM. If it's responding, inspect deeper into the wiring harness or consider reprogramming.
Common causes
- Damaged wiring between the ECU and TCM
- Faulty TCM
- Bad connectors
- Corrosion in the wiring harness
- Low battery voltage affecting module communications
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive if you're experiencing transmission issues, as it can worsen the problem.
Will this code come back after clearing?
Yes, it may return if the underlying issue isn't fixed, like wiring or module failure.
Why does this code sometimes pair with U0100?
U0100 indicates loss of communication with another module, often due to the same wiring issues affecting multiple modules.
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