U0079 indicates that a control module has detected the manufacturer-specific “G” communication bus (typically a CAN or serial data line) is electrically offline, open, or shorted, halting data exchange between the modules on that network segment. The code sets when the bus remains inactive beyond a calibrated timeout or when voltage levels stray outside valid ranges. It is a network integrity fault rather than a sensor or mechanical failure.
Open circuits, short-to-power, short-to-ground, or high-resistance connections in the Bus G twisted-pair harness, inline connectors, or pin headers due to corrosion, water intrusion, or chafing.
Missing, corroded, or out-of-specification termination resistors (if Bus G uses discrete 120 Ω resistors) causing signal reflection and a bus-off condition.
Voltage drop, poor ground, or supply-side fault at a module on Bus G causing it to drop off the network and trigger the bus-off detection.
A non-PCM control module on Bus G with a failed CAN transceiver that pulls the bus lines to an invalid state or creates excessive noise.
Rare failure of the PCM’s own CAN transceiver or bus interface circuitry; the PCM usually only reports the fault rather than causes it.
Almost never. The PCM typically stores U0079 because it detects the bus is electrically offline; the root cause is almost always wiring, connectors, or another module on the network. PCM failure is statistically unlikely.
It is a manufacturer-specific designation for a particular communication network segment, often a high- or low-speed CAN bus that links modules such as the transmission control unit, ABS controller, or body control module.
No. Loss of inter-module communication can disable safety systems, prevent gear selection, or trigger limp-home mode. The vehicle should be repaired before normal operation resumes.
The underlying electrical fault—such as an intermittent short, corrosion, or a failing module—remains present. The code will persist until the physical wiring or faulty module is repaired.