U0099 indicates that the high side of Vehicle Communication Bus H is reporting a voltage level above the expected range. This typically means a wiring fault, connector issue, or a module on that bus is pulling the line high, preventing normal data exchange.
Damaged insulation, chafed wires, or a short to power can raise the bus voltage above specification.
Oxidation, bent pins, or incomplete seating increase resistance and can cause a high‑voltage condition.
A missing or out‑of‑range termination resistor prevents proper line biasing, resulting in a high reading.
A malfunctioning gateway, body control module, or other node may drive the bus line high continuously.
An internal driver failure in the powertrain control module can affect Bus H, but this is uncommon compared to wiring or module issues.
No. The PCM is rarely the root cause; wiring faults, connector problems, or a faulty module on Bus H are far more common.
Yes. An open or out‑of‑spec termination resistor will prevent proper bus biasing and often triggers U0099.
Driving may be possible but communication loss can disable safety or drivetrain features; the issue should be diagnosed promptly.
Only if the code is caused by a known firmware bug affecting bus management; most cases require hardware repair.