U0098 is a network communication code indicating that the Body Control Module or other gateway module has detected an abnormally low voltage on Communication Bus H, one of the vehicle's serial data (typically CAN) networks. The 'Low' designation usually means the bus signal line is being pulled toward ground, indicating a short-to-ground, a stuck-low module, or a break in the terminating circuit. Because modern vehicles rely on this bus to exchange data between modules, a persistent low condition will typically disable communication with one or more modules on that network.
The most common cause. The Bus H wire is often routed through door boots, the trunk hinge area, under seats, or near sharp body seams where insulation wears through and the conductor shorts to ground.
Any control module on the network (body, comfort, infotainment, instrument cluster, etc.) can develop an internal short that holds the bus line low. This is the second-most-frequent cause and is identified by disconnecting modules one at a time while watching bus voltage.
Moisture intrusion and pin spread at intermediate splice packs or module connectors can produce a partial short or high-resistance path to ground, dragging the bus voltage down.
Incorrectly installed alarms, remote starters, audio equipment, fleet tracking units, or telematics that splice into the CAN/Bus H wiring frequently cause low-bus conditions.
Bus H relies on terminating resistors at each end of the network. An open termination can alter the recessive voltage, and in some topologies the controller reports this as a low-bus condition.
The engine control module is occasionally implicated, but this is genuinely uncommon for U0098. It should only be considered after all wiring, connectors, termination, and other modules have been ruled out by direct testing.
No. Despite the code often surfacing in powertrain communication, the PCM is rarely the failed component. The overwhelming majority of U0098 cases are traced to damaged wiring, a connector issue, or a shorted module elsewhere on Bus H. Replacing the PCM without first proving the bus integrity usually does not resolve the code.
It depends on which modules have lost communication. If only non-critical body systems are offline, the vehicle may still drive, but functionality such as gauges, shifter interlock, or stability control may be impaired. If critical modules drop off the network, the vehicle may not start or may enter a limp mode. Diagnosis should not be delayed.
All modules on a bus share the same two wires, so a single low-bus fault takes down communication for every module on that network. Each affected module will typically set its own U-code referencing lost communication, which is why a U0098 is often accompanied by several other network codes.
A meter or oscilloscope is used to identify the segment with the low reading, and modules on that segment are then unplugged one at a time. The module whose removal restores normal bus voltage is the one internally shorting the line. Wiring shorts are localized by flexing the harness while monitoring voltage.