U0100

What it means

This code means that one or more of the vehicle's computer modules has lost communication with the main engine and transmission computer (the ECM/PCM). It's like different parts of the car's 'nervous system' can't talk to its 'brain'.

Is it safe to drive?

This is a critical communication failure. Driving is highly unsafe as vital systems may not function, leading to loss of power, steering, braking, or other unpredictable behavior.

Most likely causes

• Faulty ECM/PCM

  high

  The engine's main computer itself may have failed, preventing it from communicating with other modules.

• Wiring/Connector Issues (CAN Bus)

  medium

  Damaged, corroded, or loose wiring in the CAN (Controller Area Network) bus system can interrupt communication.

• Faulty Ignition Switch/Relay

  low

  An issue with the ignition switch or a relay could prevent the PCM from receiving power, leading to communication loss.

• Other Module Failure

  low

  A shorted or faulty module on the same communication bus can bring down the entire network, including communication with the PCM.

Related help

• Full U0100 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?