U0004
High Speed CAN Communication Bus (+) Low
U0004 is an OBD-II diagnostic trouble code meaning: High Speed CAN Communication Bus (+) Low. Common causes: open or short circuit in the can (+) circuit, wiring harness damage. Estimated repair cost: $6–56.
Symptoms
- Unstable operation of electronic systems
- Malfunction indicator light comes on
- Lost connection with some modules
- Problems starting the engine
- Incorrect instrument readings
Causes
- Open or short circuit in the CAN (+) circuit
- Wiring harness damage
- Malfunction of one of the modules on the CAN bus
- Poor connection or corroded connectors
- Problems with module power supply
How to Fix
- Check the integrity of the CAN bus wires (+)
- Inspect connectors for corrosion or damage
- Check the power and ground of the modules on the CAN bus
- Disable the modules one by one to identify the faulty one.
- Check resistance and voltage on the CAN bus
Related codes
Error U0004 by Vehicle Brand
FAQ
What does the U0004 code mean?
U0004 is an OBD-II diagnostic trouble code that indicates: High Speed CAN Communication Bus (+) Low
What causes a U0004 error code?
The most common causes of U0004 include: Open or short circuit in the CAN (+) circuit; Wiring harness damage; Malfunction of one of the modules on the CAN bus; Poor connection or corroded connectors.
How do I fix a U0004 diagnostic trouble code?
To fix U0004: Check the integrity of the CAN bus wires (+). Inspect connectors for corrosion or damage. Check the power and ground of the modules on the CAN bus. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with U0004?
Do not drive — repair immediately
How much does it cost to fix U0004?
The estimated repair cost for U0004 is $6–56. Actual cost depends on your vehicle, location, and labor rates.
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