U0008 Trouble Codes and Diagnostics

The diagnostic trouble code (DTC) U0008 is related to the High-Speed Controller Area Network (CAN) communication bus. It indicates that the CAN bus (-) line is experiencing abnormally high voltage, which interferes with communication between the vehicle’s electronic control units (ECUs).

The CAN bus allows ECUs (e.g., engine control module, transmission control module, ABS, etc.) to communicate with each other efficiently.

Symptoms:

Communication Errors, Warning Lights, Loss of Functionality, Starting Issues, Intermittent Problems

Possible Causes of U0008 Code :

• Wiring Issues:

1. Short to voltage on the CAN (-) line.
2. Open circuit or damaged insulation on the CAN (-) line.
3. Corrosion in connectors or wiring harnesses.

• Faulty Control Modules:

1. One or more ECUs may be malfunctioning and sending incorrect voltage levels.
2. Improper grounding of a module.

• Connector Problems:

1. Loose or damaged pins in the CAN bus connectors.
2. Corrosion or moisture in connectors.

• Electrical Interference:

1. Aftermarket installations (e.g., radios, alarms) interfering with the CAN bus.
2. Faulty termination resistors.

• Environmental Factors:

1. Water intrusion in wiring or connectors.
2. Physical damage from an accident or rodents.

How to Fix It?

Be sure to check for any damaged components and inspect the connector pins for signs of being broken, bent, pushed out, or corroded.

Common Diagnoses and Repairs:

• Scan for DTCs: Use an OBD-II scanner to check for related CAN bus codes across all modules.
• Inspect Wiring:

1. Look for damaged, corroded, or shorted wires in the CAN (-) line.
2. Pay attention to the CAN bus wiring near high-heat or high-vibration areas.

• Check Connectors:

1. Inspect all CAN bus connectors for damage, corrosion, or loose pins.
2. Clean and re-secure connectors as necessary.

• Test Termination Resistors: Use a multimeter to check the resistance between CAN (+) and CAN (-) lines. It should be ~60 ohms.
• Module Isolation: Disconnect one module at a time to identify if a specific ECU is causing the issue.
• Check Voltage Levels: Use an oscilloscope or multimeter to measure the CAN (-) line voltage. It should be around 0-2.5V.
• Inspect Aftermarket Installations: Remove or isolate aftermarket devices to rule out electrical interference.