AutoCodes – Generic – U0049

U0049 Code - Vehicle Communication Bus 'C' (+) 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: U0049 indicates Vehicle Communication Bus 'C' (+) 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 2,780

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 U0049 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 U0049 - Vehicle Communication Bus 'C' (+) Low - AutoCodes.com — U0049 Code - Vehicle Communication Bus 'C' (+) Low

What does this mean?

What are the Possible Causes of the DTC U0049?

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 U0049?

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 U0049 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 U0049 code?

Need more information on how to fix the U0049 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0049 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 U0049 Code

1. What does OBDII code U0049 mean?

Code U0049 indicates a low voltage issue on the Vehicle Communication Bus 'C' (+), which can disrupt communication between vehicle modules.

2. What are the common symptoms of code U0049?

Symptoms may include warning lights on the dashboard, erratic or loss of communication between modules, or failure of certain electronic systems like ABS or traction control.

3. What causes code U0049 to set?

Common causes include damaged or corroded wiring, poor connections in the communication circuit, failed control modules, or a short to ground in the bus system.

4. Can a weak battery cause code U0049?

Yes, a weak or failing battery can lead to low voltage in the communication bus, potentially triggering this code.

5. How do you diagnose code U0049?

Diagnosis typically involves inspecting the wiring and connectors for damage or corrosion, checking the voltage and resistance of the bus circuit, and using a scan tool to identify communication issues.

6. Can I drive with code U0049 active?

Driving with this code active is not recommended, as it can lead to unpredictable behavior of critical vehicle systems like braking or steering.

7. What repairs can resolve code U0049?

Repairs may include fixing or replacing damaged wiring, cleaning corroded connectors, replacing a faulty module, or addressing voltage supply issues.

8. How much does it cost to fix code U0049?

Repair costs vary depending on the cause, ranging from $100 for minor wiring fixes to $1,000 or more if a control module needs replacement.

9. Can clearing the code fix the problem?

Clearing the code without addressing the underlying issue may temporarily remove the warning, but the problem will likely return.

10. What tools are needed to troubleshoot code U0049?

Youâ€™ll need a scan tool capable of reading manufacturer-specific codes, a multimeter for testing voltage and resistance, and possibly an oscilloscope to monitor bus signals.