U0021
Low Speed CAN Communication Bus (+) Open
U0021 is an OBD-II diagnostic trouble code meaning: Low Speed CAN Communication Bus (+) Open. Common causes: physical damage to can bus wires, short circuit in can circuit. Estimated repair cost: $6–56.
Symptoms
- Secondary systems do not work or work incorrectly (climate control, audio system)
- Multiple related errors appearing on different systems
- Check Engine Light Is On
- Problems with diagnostics (some modules may not be read)
Causes
- Physical damage to CAN bus wires
- Short circuit in CAN circuit
- Poor contact in module connectors
- Fault in one of the modules connected to the bus
- Corroded contacts or damaged wiring harness
How to Fix
- Visual inspection of the CAN bus wiring harness for damage
- Checking the integrity of wires and the quality of contacts in connectors
- Diagnostics of resistance and voltage in the CAN bus
- Disabling modules one by one to identify a faulty component
- Repairing or replacing damaged wires or connectors
Related codes
Error U0021 by Vehicle Brand
FAQ
What does the U0021 code mean?
U0021 is an OBD-II diagnostic trouble code that indicates: Low Speed CAN Communication Bus (+) Open
What causes a U0021 error code?
The most common causes of U0021 include: Physical damage to CAN bus wires; Short circuit in CAN circuit; Poor contact in module connectors; Fault in one of the modules connected to the bus.
How do I fix a U0021 diagnostic trouble code?
To fix U0021: Visual inspection of the CAN bus wiring harness for damage. Checking the integrity of wires and the quality of contacts in connectors. Diagnostics of resistance and voltage in the CAN bus. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with U0021?
Yes, but get it checked soon
How much does it cost to fix U0021?
The estimated repair cost for U0021 is $6–56. Actual cost depends on your vehicle, location, and labor rates.
See also: Russian version · NationStat