U0100 — Lost Communication With ECM/PCM A

What it means

Another control unit no longer receives the expected CAN bus messages from the engine control module for a defined time. On the CAN network the engine module is the main source of load, speed and torque data, so its silence disables many functions at once: transmission strategy, stability control, cluster gauges and starting. The car may fail to start, stall, or run with several warning lamps lit.

Likely causes (most common first)

1. Broken, shorted or chafed CAN high or CAN low wire in the bus harness
2. Loss of power or ground to the engine control module: blown fuse, bad relay, corroded ground point
3. Corroded or water filled connector at the module or in a bus splice
4. A different module dragging the bus down, for example one with an internal short
5. Missing or damaged bus terminating resistor, resistance far from the usual 60 ohm
6. Failure of the engine control module itself

Can you drive with it?

Do not drive: the engine can cut out and safety systems such as ABS and stability control may be disabled.