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U0040: Vehicle Communication Bus B (+) Low

What Does U0040 Mean?

U0040 is a diagnostic trouble code indicating: Vehicle Communication Bus B (+) Low. This code relates to the network communication system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

What To Do Next

  1. 1
    Find your vehicle above

    Click your make and model for real owner reports and common causes specific to your vehicle.

  2. 2
    Check for recalls

    Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.

  3. 3
    Get a professional diagnosis

    A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

Related Codes

U0035 Vehicle Communication Bus A (-) High U0036 Vehicle Communication Bus A (-) shorted to Bus A (+) U0037 Vehicle Communication Bus B U0038 Vehicle Communication Bus B Performance U0039 Vehicle Communication Bus B (+) Open U0041 Vehicle Communication Bus B (+) High U0042 Vehicle Communication Bus B (-) Open U0043 Vehicle Communication Bus B (-) Low