What it means
A fault is detected on the negative conductor of vehicle communication bus H; the code descriptor specifies a low condition. Which functions are affected depends on the vehicle’s network design.
How it works
Bus H uses paired positive and negative conductors to carry messages among its connected modules. U0098 indicates that the negative conductor is being detected at an abnormally low level, which can interfere with communication on bus H.
Common causes
Most likely first.
- Short to ground or damaged bus H negative wire
- Loose or corroded connector
- A module or gateway fault
Symptoms
- Communication faults in modules using bus H
- Warning lights or messages
- Functions relying on bus H may be unavailable
How to diagnose it
- Scan the vehicle for U0098 and companion network codes, recording affected modules and any event data that shows when the low condition occurred.
- Identify the bus H negative wire and connector locations from the wiring information, then inspect for a short to ground, crushed insulation, corrosion, or loose pins.
- Check the negative conductor's signal or electrical condition using the manufacturer's specified procedure to confirm the low reading.
- With power isolated as directed, test the negative wire for an unintended ground and check continuity through its connectors.
- If the wiring is sound, use the manufacturer's isolation procedure to determine whether a module or gateway is pulling the negative line low.
Common fixes
- Clean and secure a corroded or loose bus H negative connector.
- Repair damaged insulation or wiring causing the negative conductor to contact ground.
- Repair or replace a module or gateway confirmed to be pulling the line low.
Can I keep driving?
Keep driving only if the vehicle remains predictable and the affected bus H functions are not safety-critical. If important controls or warnings become unreliable, stop safely and have the network checked, because the fault can disable connected functions.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.