AutoCodes – Generic – U0242

U0242 Code - Lost Communication With Headlamp Control Module 'B'

Quick Answer

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Common causes include Faulty Headlamp Control Module 'B', Headlamp Control Module 'B' harness is open or shorted, Headlamp Control Module 'B' circuit poor electrical connection. 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: U0242 indicates Lost Communication With Headlamp Control Module 'B'.
Common causes: Common causes include Faulty Headlamp Control Module 'B', Headlamp Control Module 'B' harness is open or shorted, Headlamp Control Module 'B' circuit poor electrical connection.
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 8,407

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 Apr 04, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U0242 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 periodic message from the Headlamp Control Module 'B' has not been received.

OBDII Code U0242 - Lost Communication With Headlamp Control Module 'B' - AutoCodes.com — U0242 Code - Lost Communication With Headlamp Control Module 'B'

What does this mean?

What are the Possible Causes of the DTC U0242?

Faulty Headlamp Control Module 'B'
Headlamp Control Module 'B' harness is open or shorted
Headlamp Control Module 'B' circuit poor electrical connection

How to Fix the DTC U0242?

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 U0242 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.

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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 U0242 Code

1. What does the OBDII code U0242 mean?

U0242 indicates a loss of communication with the Headlamp Control Module 'B,' meaning the vehicle's systems cannot communicate with this specific module.

2. What are the common symptoms of the U0242 code?

Common symptoms include malfunctioning or inoperative headlights, warning lights on the dashboard, and possible issues with automatic headlamp adjustments.

3. What causes the U0242 code to appear?

The code can be caused by faulty wiring, a damaged Headlamp Control Module 'B,' a failed network connection, or a software glitch in the vehicle's communication system.

4. Can I still drive my car with the U0242 code?

Yes, but your headlights or related functions may not work properly, which can compromise visibility and safety, especially at night or in bad weather.

5. How do you diagnose the U0242 code?

Diagnosis involves using an OBDII scanner to confirm the code, inspecting wiring and connectors for damage or corrosion, and testing the Headlamp Control Module 'B' for proper operation.

6. What are common fixes for the U0242 code?

Common fixes include repairing or replacing damaged wiring, cleaning corroded connectors, reprogramming the module, or replacing the Headlamp Control Module 'B' if it is faulty.

7. How much does it cost to fix the U0242 code?

Repair costs vary but can range from $50 for minor wiring repairs to $500 or more if the Headlamp Control Module 'B' needs replacement.

8. Can a dead battery cause the U0242 code?

Yes, a weak or dead battery can disrupt communication between modules and cause this code to appear.

9. Is the U0242 code a manufacturer-specific issue?

No, U0242 is a generic OBDII code, but the specific symptoms and solutions may vary depending on the vehicle make and model.

10. Can a software update fix the U0242 code?

In some cases, updating the vehicle's software or reprogramming the module can resolve communication issues and clear the U0242 code.

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