OBD2 U0028

Severity

Summary

Code U0028 indicates an issue with Vehicle Communication Bus A in the vehicle area network (VAN), which is responsible for data transmission between various controllers and modules.

Symptoms

• Engine drivability concerns
• Erratic transmission shift patterns
• Lighting malfunctions or inoperative lighting
• Illumination of service engine soon lamp, traction control lamp, or antilock brake lamp
• Diminished climate control system performance
• Inoperative or erratic speedometer or odometer operation
• Power door lock or power window malfunctions

Common Causes

• Defective power relays
• Faulty or blown fuses or fusible links
• Cut, burnt, or damaged wiring harnesses or connectors
• A defective PCM or other controller
• PCM or controller programming errors

Diagnosis

1. Inspect system wiring, connectors, battery cables, and terminals.
2. Test fuses, circuit breakers, and power supply relays under load.
3. Retrieve stored trouble codes and freeze-frame data.
4. Determine the specific section of VAN or controller involved using a service manual.
5. Use diagnostic tools to check for input signals from controllers.
6. Perform resistance and continuity tests on individual circuits.

Fixes

• Repair or replace damaged wiring, connectors, fuses, relays, or defective control modules as needed.

FAQ