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All codes/U0039

U0039

Vehicle Communication Bus B (+) Open

High severity

Bus B high-side line is open — broken wire or disconnected. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

Bus B high-side line is open — broken wire or disconnected. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

Common causes

  • Wire broken or connector unplugged

    One of the most commonly reported causes for this code — check this first.

    high

    Typical part cost: $90-1100

  • Gateway module routing CAN messages incorrectly

    Less common, but worth ruling out after the more likely causes.

    low

    Typical part cost: $90-1100

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First things to check

  1. 1Confirm the code with a scan tool and check for additional related codes.
  2. 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.

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Related codes

See related trouble codes

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Frequently asked questions

What does U0039 mean?

U0039 means "Vehicle Communication Bus B (+) Open". It is a generic OBD-II code that points to a fault in the network / communication.

What are the most common causes of U0039?

wire broken or connector unplugged; gateway module routing can messages incorrectly; can terminating resistor (120 ω) drifted out of spec — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.

Can I keep driving with this code?

This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.

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