Lost Communication With Transmission Control Module (TCM)
The engine control module is not receiving data from the transmission control module.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
Your car’s engine computer is trying to talk to the transmission computer, but they're not connecting. It’s like a phone call that’s dropped because one phone is off or broken.
What the computer is actually seeing
The engine control module (ECM) sees zero signals or responses from the transmission control module (TCM) for more than 1 second when it should be receiving regular updates.
What a healthy reading looks like
Voltage should be around 12V on the data lines; if the TCM is powered and awake, the communication lines should output valid data signals.
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.
- 1Check for blown fuses related to the transmission control module and replace if needed.
- 2Inspect wiring and connectors between the ECM and TCM for damage or loose connections.
- 3Use a scan tool to check for any other codes that may indicate issues with the transmission system.
- 4Verify power and ground to the transmission control module with a multimeter (expected around 12V).
- 5If TCM is receiving proper power and ground, but the problem persists, consider testing/reshimming the TCM or replacing it.
Common causes
- Faulty TCM
- Wiring issue (broken or corroded wires) between ECM and TCM
- Bad connectors or loose connections
- Faulty ECM
- Software issue in the TCM
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
No, driving with this code can prevent the vehicle from shifting properly, which can lead to transmission damage.
Will the code come back after clearing it?
It may come back if the underlying issue isn’t fixed, such as a wiring problem or a bad TCM.
Why does this code pair with U0101 sometimes?
U0101 and U0102 are related and indicate communication issues; if one is present, the other may appear due to similar underlying problems.
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