Lost Communication With Transmission Control Module (TCM)

What it means

Another module, usually the engine computer (ECU), the instrument cluster or the ABS module, has stopped receiving messages from the transmission control module (TCM) over the CAN bus. The transmission usually goes into limp mode to protect itself. Most cases come from lost power or ground at the module, or a connector or bus wiring fault, and several U codes together point to a bus or battery problem rather than this module alone.

Related codes: U0100U0001U0073U0402P0700P0562

Symptoms5

• Transmission in limp mode, stuck in one gear.
• Harsh or delayed shifts, or no shifting at all.
• Check engine light on, sometimes with the gear indicator missing from the cluster.
• Scan tool cannot communicate with the transmission module.
• No start on some vehicles because the park signal does not arrive.

Possible causes6

• Weak battery or loose terminals.
• Blown transmission module power fuse or faulty relay.
• Corrosion, oil or water in the module connector, especially when it is mounted on the transmission.
• Poor ground connections.
• Open or shorted bus wiring to the module.
• Internal module failure from heat, water or a voltage spike.

How to diagnose5

1. Read codes from all modules; if many modules report lost communication, start with the battery and the bus, and if only the transmission control module is missing, focus on it.
2. Try to communicate with the transmission control module directly with a scan tool; no response points to lost power, ground or wiring to it.
3. Locate the transmission control module from the manufacturer information, since on some vehicles it is built into the engine computer and on others it is separate or mounted on or inside the transmission, then check its power fuse and measure power and ground at its connector.
4. Inspect the module connector for water, corrosion or loose terminals, and check the bus wiring to it.
5. Disconnect the battery and measure resistance between the CAN bus wires at the module connector, comparing with the manufacturer specification to find an open or short.

How to fix6

1. Charge or replace the battery, and clean and tighten its terminals.
2. Replace the blown fuse after finding why it blew.
3. Clean the module connector and repair the ground or damaged bus wiring.
4. Update the module software if the manufacturer has an update.
5. Replace the transmission control module if proven faulty with good power and bus wiring, then program and code it to the vehicle.
6. Clear codes in all modules and confirm the code does not return.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a battery, fuse or connector, rises with wiring repairs, and is highest if the transmission module must be replaced and programmed, especially when it is built into the transmission.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions