Lost Communication with TCM
The PCM cannot communicate with 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)
What’s happening is your car’s main computer (PCM) is trying to talk to the transmission’s computer (TCM), but it’s not getting any response. It’s like trying to call someone on the phone and they don’t answer.
What the computer is actually seeing
The PCM detects no communication signals from the TCM. This is often shown by a voltage drop or absence of data within expected communication protocols.
What a healthy reading looks like
Expected data transfer between PCM and TCM usually occurs under a 1.5 ms burst with voltage levels around 0.5V to 5V for signal integrity.
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 the TCM power and ground circuits. Expect battery voltage at the power feed and near zero volts for ground.
- 22. Inspect wiring harness and connectors between PCM and TCM for physical damage, corrosion, or loose connections.
- 33. Verify that other modules are communicating properly. Use a scan tool to check for communication with other computers in the network.
- 44. If the wiring and connectors check out but the code persists, consider swapping the TCM with a known good unit to eliminate it as the cause.
- 55. If the replacement TCM does not resolve the issue, suspect a fault in the PCM itself.
Common causes
- Faulty Transmission Control Module (TCM)
- Damaged wiring or connectors between the PCM and TCM
- Faulty main PCM
- Low battery voltage affecting communication
- Corrosion or bad ground in the circuit
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
No, it’s not safe. You may experience erratic shifting or limp mode, leading to potential safety hazards.
Will this code come back after repairs?
If the root cause is addressed, it shouldn’t return. However, if there are underlying wiring issues, it might.
Why do I see this code with U0100?
Both codes relate to communication issues within the vehicle's network. U0100 is for general lost communication, while U1100 specifically points to the TCM.
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