What are the symptoms of U0100?

Multiple warning lights across clusters — ABS, SRS, traction control all on simultaneously. Instrument cluster gauges dropping to zero. Engine may not start. Transmission stuck in limp mode

Check battery voltage and terminal connections first — low voltage causes false U-codes. Verify PCM power and ground circuits with a DVOM (should read battery voltage and <0.1 Ω ground resistance). Inspect main engine harness connectors at PCM for corrosion or pushed-back pins. Use advanced scan tool to check CAN bus health; look for bus-off errors indicating a module pulling the bus low

U0100

Lost Communication With ECM/PCM

Q: What does U0100 mean?

A control module on the CAN bus cannot communicate with the Engine Control Module.

🔴 CRITICAL — STOP DRIVING NETWORK · CAN Bus

A control module on the CAN bus cannot communicate with the Engine Control Module.

What You'll Notice

Multiple warning lights across clusters — ABS, SRS, traction control all on simultaneously
Instrument cluster gauges dropping to zero
Engine may not start
Transmission stuck in limp mode

Probable Causes

CAN bus wiring fault — chafed, corroded, or accidentally cut harness
Failed PCM / ECM module
Bad PCM ground or power supply circuit
Corroded battery terminals causing intermittent voltage drop on CAN network

Direct Repair Steps

Check battery voltage and terminal connections first — low voltage causes false U-codes
Verify PCM power and ground circuits with a DVOM (should read battery voltage and <0.1 Ω ground resistance)
Inspect main engine harness connectors at PCM for corrosion or pushed-back pins
Use advanced scan tool to check CAN bus health; look for bus-off errors indicating a module pulling the bus low

Vehicles Affected

chevy ford gmc dodge jeep bmw honda toyota