Vehicle Trouble Codes and Diagnostics

The U0012 OBD-II code signals an issue with the Medium Speed CAN Communication Bus (+) being open. This pertains to a fault in the CAN (Controller Area Network) communication system, specifically the medium-speed bus that facilitates communication between different vehicle modules. An open circuit on the Medium Speed CAN Bus (+) means that the system is not receiving the expected signals from the CAN bus. This issue typically involves the medium-speed bus, which is used for data transfer between various modules, unlike the high-speed CAN bus, which handles more critical functions like communication with the powertrain control module, body control module, and transmission.

Symptoms:

Check Engine Light (CEL), Communication Problems, Poor Vehicle Performance, Difficulty with Diagnostics

Possible Causes of U0012 Code :

• Wiring Issues: Damaged or corroded wiring or connectors, poor insulation, or a broken wire along the CAN bus circuit.
• Faulty CAN Bus Module: A malfunction in one of the electronic control units (ECUs) connected to the medium-speed CAN bus.
• Faulty Bus Termination: The bus might not be properly terminated, or resistors may be faulty.
• Loose or Corroded Connectors: Issues with the physical connection between the bus and its modules.
• Short Circuit or Grounding Issue: A short circuit or improper grounding could lead to the CAN signal being lost.

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:

• Visual Inspection: Check for damaged wiring, connectors, or any visible faults on the CAN bus wiring.
• Scan for Other Codes: Look for related trouble codes that might point to a specific faulty module or part.
• Verify Bus Termination: Ensure the CAN bus is correctly terminated with appropriate resistors.
• Check Power Supply to ECUs: Ensure that all modules connected to the CAN bus are receiving proper power and grounding.