U0089 is a network communication code indicating the powertrain control module (PCM) has lost communication with a device or module on 'Bus G', a specific CAN bus circuit. This is not an emissions or engine-specific fault but rather a wiring/communication issue between control modules.
The most common cause is physical damage, corrosion, or water intrusion in the wiring harness or connectors for the modules on Bus G.
The specific module (such as a body control module, transmission control module, or sensor) connected to Bus G may have failed internally.
The module on Bus G may not be receiving proper battery voltage or ground due to blown fuses, faulty relays, or bad ground connections.
A short between CAN high and low wires, or an open in one of the bus wires, can cause communication loss.
The 120-ohm termination resistors at each end of the CAN bus circuit may be defective or missing.
The PCM itself may have failed, though this is the least likely cause and should be investigated only after all other possibilities are ruled out.
Almost never. U0089 is a lost communication code indicating another module on Bus G or its wiring has failed. The PCM is the device trying to talk to something that isn't responding—it is rarely the root cause. Technicians should diagnose the affected bus and modules first.
It depends on which module has lost communication. Some vehicles may run but have limited functionality (no gauges, non-working climate controls, or limp mode). If multiple critical modules are affected, the vehicle may not start or could stall.
No. U-codes are network communication faults, not emissions-specific codes. It will not cause an emissions test failure on its own, though underlying issues affecting engine operation might.
When one module fails or the bus wiring is damaged, it can affect communication with multiple other modules, triggering several U-codes simultaneously. This is normal and helps narrow down the failed component or circuit.