U0012 indicates that the vehicle's medium‑speed CAN bus is not communicating properly, meaning messages from one or more modules are not being received. This can affect multiple vehicle systems that rely on the network.
Inspect and reseat the connectors on the CAN high and low wires; corrosion or poor contact can create an open circuit on the bus.
Check the high and low speed CAN wires for cuts, abrasions, or broken shields that interrupt the communication path.
A malfunctioning module such as the Body Control Module, Transmission Control Module, or another networked component may stop transmitting messages, appearing as an open bus.
PCM failure is rare; it typically only occurs after wiring and other modules have been verified as functional.
No. The code most commonly points to wiring or connector issues; PCM failure is rare and should be considered only after other causes are ruled out.
You may be able to drive, but some vehicle functions could be limited or intermittent. It is advisable to address the issue promptly to avoid further complications.
Clearing the code without repairing the underlying communication fault will usually cause the code to reappear once the fault is detected again.
U0012 is a generic SAE-defined code for a medium‑speed CAN bus open condition, though individual manufacturers may have additional notes or related codes.