OBD2 U0101: Lost Communication with TCM

Error code

OBD2U0101

Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Lost Communication with TCM.

Severity

highThe vehicle may be drivable but with significant transmission issues. It is recommended to address the issue promptly.

Summary

U0101 indicates a loss of communication with the Transmission Control Module (TCM), which can affect transmission shifting and overall vehicle performance.

Symptoms

Check Engine light illuminated
Transmission shifts erratically
Transmission stuck in 2nd gear or limp mode
PRNDL display inaccurate or not working
Diagnostic scan tool won't power up

Common Causes

Broken or damaged wiring (sometimes rodent-related)
IOD fuse poor connection
Low battery voltage
Transmission control module internal short
Bent connector pins
Corrosion on wiring or connectors

Diagnosis

Check for service bulletins from your vehicle manufacturer.
Verify that the PCM has the correct VIN if it was recently replaced.
Inspect the IOD fuse and ensure a good connection.
Use a quality scan tool and digital volt-ohmeter (DVOM) to trace issues.
Check the main connector at the TCM for 12V power and proper ground.
Inspect wiring connectors for corrosion, moisture, and bent pins.
Test CANbus circuit resistance using DVOM.

Fixes

Repair damaged or corroded wires and ensure secure connections.
Replace the TCM if internal failure is suspected, requiring professional programming.

FAQ

What should I do if my diagnostic scan tool won't power up?

Check the DLC fuse and ensure it is not burnt. If necessary, replace the fuse.

How can I verify that the TCM is active on the network?

Use a quality scan tool to check if the TCM is active on the CANbus network.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

All OBD2 codes →Search more codes →

OBD2 U0101