AutoCodes – Generic – U0074

U0074 Code - Control Module Communication Bus 'B' Off

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: U0074 indicates Control Module Communication Bus 'B' Off.
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 29,107

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 U0074 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 U0074 - Control Module Communication Bus 'B' Off - AutoCodes.com — U0074 Code - Control Module Communication Bus 'B' Off

What does this mean?

What are the Possible Causes of the DTC U0074?

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 U0074?

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 U0074 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 U0074 code?

Need more information on how to fix the U0074 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0074 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U0074 Buick — Control Module Communication Powertrain Expansion CAN Bus Off Malfunction
U0074 Cadillac — Control Module Communication Powertrain Expansion CAN Bus Off Malfunction
U0074 Chevrolet — Control Module Communication Powertrain Expansion CAN Bus Off Malfunction
U0074 Ford — Control Module Communication Bus 'B' Off
U0074 GMC — Control Module Communication Powertrain Expansion CAN Bus Off Malfunction
U0074 Lincoln — Control Module Communication Bus 'B' Off
U0074 Mercury — Control Module Communication Bus 'B' Off

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 U0074 Code

1. What does the OBDII code U0074 mean?

The code U0074 indicates that there is a communication issue on the Control Module Communication Bus 'B,' suggesting that the bus is offline and not transmitting or receiving any signals.

2. What symptoms might I notice if my car has the U0074 code?

Symptoms can include the check engine light turning on, the vehicle entering a limp mode, or various electronic systems (such as ABS, traction control, or airbags) becoming non-operational.

3. What are common causes of the U0074 code?

Common causes include faulty control modules, damaged wiring harnesses, poor electrical connections, or a malfunctioning CAN (Controller Area Network) bus.

4. How can I diagnose the U0074 code in my vehicle?

Diagnosing this code typically involves using a scan tool to monitor the communication bus, checking for damaged wires or loose connections in the communication network, and possibly testing individual control modules for faults.

5. What steps should be taken to fix the U0074 code?

Repairing the U0074 code may involve replacing damaged wires or connectors, repairing or replacing faulty control modules, and ensuring all connections in the communication network are secure.

6. Is it safe to drive a vehicle with the U0074 code?

While the vehicle can often still operate, driving with the U0074 code can be risky as critical systems like braking or steering aids may malfunction. It is advisable to address the issue promptly.

7. How urgent is it to repair a car with the U0074 code?

It is fairly urgent to repair this issue due to the potential failure of essential safety-related vehicle systems. Delaying repairs could lead to unsafe driving conditions.

8. Can a U0074 code impact the vehicle's fuel economy?

Although U0074 primarily affects communication between control modules, indirect effects such as the vehicle entering limp mode can alter driving performance and potentially impact fuel economy.

9. What tools are needed to diagnose and repair the U0074 code?

Essential tools include a professional OBDII scanner, a digital multimeter, and potentially an oscilloscope to check the integrity and signals on the communication bus.

10. Could a U0074 code indicate a problem with the vehicleâ€™s ECU?

Yes, a U0074 code could be indicative of a problem with the ECU (Engine Control Unit) or other critical control modules, as it signals an interruption in communication which could be due to a malfunctioning ECU.