U0119 indicates the vehicle's main computer (PCM/ECM) has lost communication with the Fuel Cell Control Module (FCCM) on the controller area network (CAN). This is a network communication fault, not an emissions or sensor issue, and it commonly affects fuel cell electric vehicles like the Toyota Mirai and Hyundai Nexo.
The FCCM itself has internal electrical failure, which is the most common cause when communication is permanently lost.
Physical damage to the FCCM harness, corroded connectors, or broken pins between the FCCM and the CAN bus can interrupt communication.
A failed fuse or relay that supplies power to the FCCM will cause it to go offline, resulting in lost communication.
A short, open, or interference on the CAN bus network that affects the FCCM circuit specifically.
Loose, dirty, or oxidized connectors at the FCCM or the PCM can cause intermittent communication loss.
The PCM itself is very rarely the cause; it should be diagnosed last after all other possibilities are ruled out.
No. The PCM is almost never the cause of U0119. In the vast majority of cases, the problem is the Fuel Cell Control Module itself, its wiring, connectors, or power supply. Replacing the PCM is almost never the correct fix.
It is not recommended. Depending on the vehicle, you may experience no-start conditions, reduced power, or the fuel cell system may shut down completely for safety reasons. Have it diagnosed promptly.
U0119 is relatively rare because it only applies to fuel cell electric vehicles, which represent a very small fraction of vehicles on the road. The code is more common in Toyota Mirai and Hyundai Nexo vehicles.
Some technicians may not be familiar with fuel cell systems and default to replacing the main computer when they see a communication fault. A competent diagnosis should always check the module, its power supply, and wiring first before suspecting the PCM.