What it means
A fault is detected on the negative conductor of vehicle communication bus G; the code descriptor specifies a low condition. Which functions are affected depends on the vehicle’s network design.
How it works
Bus G's negative conductor is part of the path that allows connected modules to exchange messages. U008F sets when that conductor is detected at a lower level than expected, which can impair communication on bus G.
Common causes
Most likely first.
- Short to ground or damaged bus G negative wire
- Loose or corroded connector
- A module or gateway fault
Symptoms
- Communication faults in modules using bus G
- Warning lights or messages
- Functions relying on bus G may be unavailable
How to diagnose it
- Scan all modules for bus G codes and note which modules lose communication to narrow down the affected section.
- Review freeze-frame or event data and live network status to determine when the negative-line low condition occurs.
- With power isolated according to the manufacturer's instructions, inspect bus G negative wiring and connectors for shorts to ground, chafing, corrosion, or loose terminals.
- Test the negative conductor for an unintended short to ground and check continuity through suspect sections using the manufacturer's procedure.
- If wiring tests pass, isolate bus G modules and the gateway as directed to identify a unit pulling the negative conductor low.
Common fixes
- Secure a loose bus G negative connector and clean corroded terminals.
- Repair damaged negative-conductor insulation or wiring causing a short to ground.
- Repair or replace faulty connector terminals on the bus G negative circuit.
- Repair or replace the module or gateway confirmed to be pulling the negative line low.
Can I keep driving?
The fault can disable functions whose modules communicate over bus G, so drive only if those functions are not essential to safe operation. Stop driving if any safety-related system is affected or behaves unpredictably.
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.