U0055 is a network communication code indicating a malfunction on the vehicle's 'Bus D' communication line, one of several data buses that allow control modules to exchange information. The code is set when one or more modules detect that they cannot transmit or receive valid messages on this bus, pointing to a wiring, connector, termination, or module-level fault rather than a sensor or mechanical problem.
Broken, pinched, or corroded wires between modules on Bus D are the most common cause. Harness damage at body hinges, ground points, and areas that flex during normal use is a frequent culprit.
Connectors at the modules on Bus D often develop pin corrosion, moisture intrusion, or spread terminals that increase resistance and distort the data signal.
If one module's internal transceiver fails, it can drag the bus voltage down and block communication for every other module on the same bus segment.
Most CAN-style buses rely on termination resistors at each end of the bus (commonly around 120 ohms total). An open, shorted, or missing resistor causes signal reflections and communication errors.
Moisture inside a connector or conduit, and rodent-chewed insulation, both create intermittent or hard communication faults on the bus.
The PCM's network transceiver can fail, but this is uncommon. Most U0055 cases trace to wiring, connectors, another module, or termination issues, not the PCM itself.
It depends on which systems are affected. The engine may still run, but features like ABS, airbags, stability control, or the instrument cluster may be disabled. Drive only if critical systems remain functional and have the fault diagnosed as soon as possible.
Usually no. U0055 is set when the wiring, a connector, a termination resistor, or another module on Bus D is disrupting communication, and the PCM is most often a victim reporting the problem rather than the cause. Replacing the PCM without first checking the harness, connectors, other modules, and bus termination rarely resolves U0055 and can waste money.
Many vehicles use multiple data buses (sometimes labeled A, B, C, D, etc.) to separate high-speed powertrain traffic from lower-speed body or convenience traffic. Bus D is simply the label for one of these segments; which modules sit on it and its data rate depend on the specific vehicle platform.
A scanner capable of reading codes from multiple modules is helpful, and a graphing multimeter or lab scope is usually needed to check bus voltages and termination resistance. A wiring diagram that shows which modules are on Bus D is also strongly recommended for an efficient diagnosis.