AutoCodes – Generic – U0039

U0039 Code - Vehicle Communication Bus 'B' (+) Open

Quick Answer

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Common causes include Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s), Check for more codes, Faulty Control Module. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: U0039 indicates Vehicle Communication Bus 'B' (+) Open.
Common causes: Common causes include Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s), Check for more codes, Faulty Control Module.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 3,554

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 29, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U0039 Description

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits. CAN bus uses two dedicated wires for communication. The wires are called CAN high and CAN low. When the CAN bus is in idle mode, both lines carry 2.5V. When data bits are being transmitted, the CAN high line goes to 3.75V, and the CAN low drops to 1.25V, thereby generating a 2.5V differential between the lines. Since communication relies on a voltage differential between the two bus lines, the CAN bus is NOT sensitive to inductive spikes, electrical fields, or other noise. The Diagnostic Trouble Code (DTC) sets when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U0039 - Vehicle Communication Bus 'B' (+) Open - AutoCodes.com — U0039 Code - Vehicle Communication Bus 'B' (+) Open

What does this mean?

What are the Possible Causes of the DTC U0039?

Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s)
Check for more codes
Faulty Control Module
Control Module harness is open or shorted
Control Module circuit poor electrical connection

How to Fix the DTC U0039?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U0039 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the U0039 code?

Need more information on how to fix the U0039 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0039 code diagnosed by a professional: Find a repair shop in your area

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about U0039 Code

1. What does the OBDII code U0039 indicate?

The U0039 code signifies an issue with the Vehicle Communication Bus 'B' (+) Open, indicating a problem in the communication line used by the vehicle's control modules to exchange information. This could be due to a break or disconnection in the bus.

2. What are the common symptoms of code U0039?

Symptoms may include the malfunction indicator lamp (MIL) lighting up, various electrical components not functioning properly, issues with the vehicleâ€™s performance, and possible problems in systems such as ABS, airbags, or transmission control.

3. What can cause the U0039 code to appear?

Potential causes include damaged wiring or connectors in the communication bus, a fault in one of the control modules, or a poor electrical connection that interrupts the bus communication.

4. How is the U0039 code diagnosed?

Diagnosis involves using a scan tool to read the trouble code from the vehicle's onboard computer, inspecting the wiring and connectors for damage or corrosion, and checking the continuity and resistance in the communication bus lines.

5. What are the steps to repair a vehicle showing the U0039 code?

Repair steps typically include repairing or replacing any damaged wiring or connectors, ensuring all connections are secure, and possibly replacing faulty control modules if they are determined to be the issue.

6. Can I drive my car if it shows a U0039 code?

While you might be able to drive the vehicle, it's not recommended as the underlying communication issue could affect critical systems like braking or steering assistance, potentially compromising vehicle safety.

7. What tools are needed to diagnose the U0039 code?

Tools needed include a professional-grade scan tool capable of interfacing with the vehicle's communication network, a digital multimeter for electrical tests, and possibly an oscilloscope to analyze the signals on the communication bus.

8. How long does it typically take to fix the U0039 code?

The repair time can vary widely depending on the specific cause of the code. Simple connector repairs might take a few hours, while tracing and repairing wiring issues or replacing components can take significantly longer.

9. Is the U0039 code a serious concern?

Yes, it should be considered serious because it affects the vehicleâ€™s communication network, which is crucial for the operation of various control modules and systems within the vehicle.