Code U0077 indicates that the vehicle's on-board diagnostics have detected a loss of communication on 'Bus E,' a specific data network used by control modules. This means modules assigned to this network are unable to exchange data, which may disable specific vehicle features.
Physical damage to the communication wires, such as chafing, rodent damage, or broken conductors, causing an open or short circuit.
Moisture intrusion or loose pins at the module connectors leading to intermittent or total loss of signal.
An internal hardware failure within one of the modules connected to Bus E, preventing it from broadcasting or receiving data.
A weak battery or failing alternator causing modules to under-voltage and drop off the communication network.
A failure in the main engine or body control module's network interface, though this is less common than wiring issues.
No. While the PCM is involved in networking, U-codes are far more likely to be caused by wiring faults, connector corrosion, or the failure of a peripheral module rather than the PCM itself.
Yes. Many control modules require a specific voltage threshold to operate; if the voltage drops too low, the module may shut down, causing the rest of the network to report a communication loss.
It depends on the systems assigned to Bus E. If critical safety systems like electronic stability control or power steering are affected, the vehicle may be unsafe to operate.