DTC U0012 – Medium Speed CAN Communication Bus Off

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DTC U0012 – Medium Speed CAN Communication Bus Off

What Does DTC U0012 Mean?

DTC U0012 indicates that the Medium-Speed Controller Area Network (MS-CAN) has entered a Bus Off condition. This occurs when excessive communication errors force a control module to temporarily disconnect itself from the CAN network. The exact definition may vary by manufacturer.

Severity

High. A Bus Off condition can interrupt communication between multiple control modules and disable several vehicle functions.

Can You Drive with U0012?

In many cases, the vehicle can still be driven, but some electronic systems may not operate correctly. The fault should be diagnosed as soon as possible.

Symptoms

  • Check Engine or communication warning light.
  • Multiple communication-related DTCs.
  • Loss of communication with one or more modules.
  • Electrical accessories malfunction.
  • Instrument cluster warning messages.

Common Causes

  • Short circuit on the CAN bus.
  • Open circuit in CAN High or CAN Low wiring.
  • Loose or corroded connectors.
  • Faulty control module disrupting network communication.
  • Low battery voltage or charging system problems.

How to Diagnose U0012

  1. Scan every control module for stored DTCs.
  2. Check battery voltage and charging system performance.
  3. Inspect CAN High and CAN Low wiring.
  4. Measure CAN bus resistance with the ignition OFF.
  5. Disconnect suspected modules one at a time if the network is down.
  6. Repair the fault and verify communication is restored.

Typical CAN Bus Layout

          PCM
           │
CAN H ─────┼──────── BCM
CAN L ─────┼──────── ABS
           │
           ├──────── Cluster
           │
           └──────── HVAC

Estimated Repair Cost

  • Battery or charging repair: $50–250
  • CAN wiring repair: $80–300
  • Connector replacement: $30–150
  • Control module replacement: $300–1,000

Related DTCs

  • U0001
  • U0010
  • U0011
  • U0013

Frequently Asked Questions

What does Bus Off mean?

Bus Off means a control module has stopped transmitting on the CAN network after detecting too many communication errors.

Can a bad battery trigger U0012?

Yes. Low voltage can cause unstable CAN communication and may contribute to a Bus Off condition.

Is U0012 the same on every vehicle?

No. The exact definition and diagnostic procedure vary between manufacturers. Always consult the factory service information for the specific vehicle.

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