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AutoCodes – Generic – U0031

U0031 Code - Vehicle Communication Bus 'A' (+) Low

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
U0031 indicates Vehicle Communication Bus 'A' (+) Low.
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 5,812
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Mar 29, 2020
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Code U0031 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 U0031 - Vehicle Communication Bus 'A' (+) Low - AutoCodes.com
U0031 Code - Vehicle Communication Bus 'A' (+) Low
What does this mean?

What are the Possible Causes of the DTC U0031?

  • 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 U0031?

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 U0031 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 U0031 code?

Need more information on how to fix the U0031 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0031 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 U0031 Code

What does the OBDII code U0031 mean?

U0031 indicates that the Vehicle Communication Bus 'A' (+) signal is operating at a lower voltage than expected, which may disrupt communication between vehicle modules.

What are the common symptoms of code U0031?

Symptoms may include warning lights on the dashboard, reduced functionality of electronic systems, communication errors between modules, or intermittent electrical malfunctions.

What causes the U0031 code to appear?

Common causes include damaged wiring or connectors in the communication bus, short circuits, module failures, or issues with the power supply to the affected bus.

Can the U0031 code cause drivability issues?

In some cases, yes. If the communication bus is critical for drivetrain or safety systems, it can lead to reduced performance or disable certain features.

How do you diagnose code U0031?

Diagnosis involves inspecting wiring and connectors for damage, testing the voltage on the communication bus, scanning for additional codes, and verifying module functionality.

Can a dead battery trigger code U0031?

Yes, a weak or dead battery can disrupt communication on the vehicle bus and potentially result in the U0031 code.

Is it safe to drive with the U0031 code?

Driving may be possible, but it's not recommended until the issue is resolved, as critical communication between modules may be compromised.

How do you fix code U0031?

Repairs typically involve fixing or replacing damaged wiring, connectors, or modules associated with the communication bus, and ensuring proper voltage and ground connections.

Can a faulty module cause the U0031 code?

Yes, a malfunctioning module can disrupt communication and result in the U0031 code being stored.

Does clearing the U0031 code fix the problem?

Clearing the code may temporarily remove it, but the underlying issue needs to be resolved to prevent the code from reappearing.

Discuss the causes and fixes for U0031 OBDII Code

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