U0140 indicates the Powertrain Control Module (PCM) or other primary controller has lost serial data communication with the Body Control Module (BCM) over the CAN bus. This means the BCM is not responding to network messages, which may be due to module failure, wiring faults, or power interruption. The code triggers when expected data packets from the BCM are absent for a calibrated period.
The module's processor or CAN transceiver has failed, preventing it from transmitting or receiving network messages despite proper power and ground.
Open circuit, short-to-ground, short-to-power, or high resistance in the CAN High or CAN Low wiring between the PCM and BCM disrupts serial communication.
Blown fuse, corroded terminals, or poor chassis ground prevents the BCM from waking up or maintaining stable operation.
Moisture intrusion, bent pins, or terminal fretting at the BCM harness connector or inline junctions creates high resistance or open circuits.
Rare internal failure of the PCM's CAN transceiver prevents it from receiving BCM messages, though the BCM or wiring is almost always the root cause.
Generally yes, though convenience features like power windows, locks, and interior lighting may fail. In some vehicles, the immobilizer may prevent starting or cause stalling if the BCM cannot communicate with the PCM.
If the module receives proper power and ground but fails to communicate on a verified intact CAN bus, replacement is typically required. New modules usually require configuration and theft-system programming.
While the PCM sets the code, PCM failure causing U0140 is rare. Most instances are caused by BCM failure or wiring issues. Verify the PCM communicates with other modules before considering PCM replacement.
Voltage spikes or connection sequence errors during battery replacement can corrupt BCM memory or damage the internal network transceiver, especially if terminals were touched together or reversed.