U0055: Vehicle Communication Bus D

What it means

A fault is detected on vehicle communication bus D. The code identifies the bus but does not specify the cause.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

Vehicle communication bus D carries messages between the modules connected to that network. A control module detects a fault affecting bus D communication and sets U0055, but the code alone does not say whether the cause is a wire, module, gateway path, or termination problem.

Common causes

Most likely first.

1. Wiring or node fault on bus D
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules for communication codes and record freeze-frame data and which bus D modules do not respond.
2. Use the wiring diagram to identify bus D modules, its gateway routing, connectors, and termination points.
3. Inspect accessible bus D wiring and connectors for damage, corrosion, loose pins, moisture, and poor prior repairs.
4. Use the scan tool to compare which bus D modules communicate and check whether the fault changes when accessible connectors or harness sections are gently moved.
5. With power isolated as required, test bus D conductors for continuity and shorts, and compare termination with the manufacturer's specification.
6. If wiring and termination pass, use the manufacturer's network procedure to isolate the gateway and individual bus D modules.

Common fixes

• Repair damaged or chafed bus D wiring found during inspection.
• Clean, reseat, or repair a loose, wet, or corroded bus D connector.
• Repair a failed splice or termination fault confirmed by testing.
• Repair or replace a gateway or bus D module only after its wiring and power and ground connections pass checks.

Can I keep driving?

If the vehicle has warnings or lost functions involving steering, braking, engine, or transmission control, stop driving and arrange assistance. If only noncritical functions are affected and the vehicle operates normally, drive cautiously and limit use until diagnosed.