AutoCodes – Generic – U0040

U0040 Code - Vehicle Communication Bus 'B' (+) 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: U0040 indicates Vehicle Communication Bus 'B' (+) 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 4,992

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 U0040 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 U0040 - Vehicle Communication Bus 'B' (+) Low - AutoCodes.com — U0040 Code - Vehicle Communication Bus 'B' (+) Low

What does this mean?

What are the Possible Causes of the DTC U0040?

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 U0040?

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 U0040 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 U0040 code?

Need more information on how to fix the U0040 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0040 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 U0040 Code

1. What are the common symptoms of OBDII code U0040 - Vehicle Communication Bus 'B' (+) Low?

The common symptoms of U0040 include issues with the vehicle's communication systems, such as loss of communication between control modules, warning lights on the dashboard, and issues with electronic components.

2. What are the possible causes of OBDII code U0040?

The possible causes of U0040 can include damaged wiring or connectors in the communication bus 'B', faulty control modules, software glitches, or issues with the communication network within the vehicle.

3. How can I diagnose OBDII code U0040?

Diagnosing U0040 typically involves using a professional OBDII scanner to retrieve the trouble codes, inspecting the wiring and connectors in the communication bus 'B', checking for loose connections, and testing the control modules for any faults.

4. Can a DIY enthusiast repair OBDII code U0040 at home?

Repairing U0040 may require advanced diagnostic tools and expertise, so it is recommended to consult a professional mechanic or automotive technician for proper diagnosis and repair to address the underlying issues effectively.

5. Is it safe to continue driving with OBDII code U0040 present?

It is not advisable to continue driving with U0040 as it can lead to potential communication failures between critical control modules in the vehicle, affecting the overall performance and safety of the vehicle.

6. How much does it typically cost to repair OBDII code U0040?

The cost of repairing U0040 can vary depending on the underlying cause of the issue, the extent of the damage, and the labor rates of the repair facility. It is recommended to get a detailed estimate from a trusted mechanic.

7. Can resetting the trouble codes clear OBDII code U0040?

Resetting the trouble codes may temporarily clear U0040, but if the underlying issue is not addressed, the code is likely to reappear. It is crucial to diagnose and repair the root cause of the problem to prevent further issues.

8. Are there any preventive measures to avoid OBDII code U0040 in the future?

Regular maintenance, timely inspections of the vehicle's communication systems, and addressing any wiring or connector issues promptly can help prevent OBDII code U0040 from occurring in the future.

9. How long does it typically take to repair OBDII code U0040?

The repair time for U0040 can vary depending on the complexity of the issue, the availability of parts, and the expertise of the mechanic. It is advisable to consult with the repair facility for an estimated timeframe.

10. Can OBDII code U0040 affect the overall drivability of the vehicle?

Yes, U0040 can affect the overall drivability of the vehicle by causing communication failures between control modules, leading to issues with various electronic systems, potentially impacting the performance and safety of the vehicle.