U0086: Vehicle Communication Bus F - Low

What it means

A fault is detected on the negative conductor of vehicle communication bus F; the code descriptor specifies a low condition. Which functions are affected depends on the vehicle’s network design.

How it works

Bus F is the communication network used by its connected modules, with separate positive and negative conductors. This code means the bus F negative conductor is being detected at an abnormally low electrical level, potentially disrupting messages across the network.

Common causes

Most likely first.

1. Short to ground or damaged bus F negative wire
2. Loose or corroded connector
3. A module or gateway fault

Symptoms

• Communication faults in modules using bus F
• Warning lights or messages
• Functions relying on bus F may be unavailable

How to diagnose it

1. Scan all modules and capture freeze-frame data and related codes to see which bus F functions are affected and when.
2. Refer to the vehicle network diagram to locate the bus F negative conductor and connected modules and gateways.
3. Inspect the negative wire and connectors for chafing, crushed insulation, moisture, corrosion, or loose terminals that could pull the line low.
4. Following the manufacturer's isolation procedure, test the negative conductor for a short to ground and check its electrical condition at accessible connectors.
5. If the wiring is intact, use the manufacturer's procedure to isolate modules and determine whether a gateway or module is pulling bus F negative low.

Common fixes

• Clean and secure a loose or corroded bus F negative connector.
• Repair insulation damage or a short to ground on the bus F negative wire.
• Repair a damaged negative-conductor terminal or connector.
• Repair or replace a confirmed module or gateway pulling bus F negative low.

Can I keep driving?

Driving may be possible if the vehicle remains controllable and affected functions are noncritical, though bus F features may fail or warnings may appear. Stop if the fault affects steering, braking, powertrain control, or another essential system.