AutoCodes – Generic – U1521

U1521 Code - Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus

Quick Answer

The Local Interconnect Network (LIN) Bus consists of a single wire with a transmission rate of 10.417 Kbit/s. Common causes include Faulty Left Headlamp, Left Headlamp harness is open or shorted, Left Headlamp 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: U1521 indicates Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus.
Common causes: Common causes include Faulty Left Headlamp, Left Headlamp harness is open or shorted, Left Headlamp 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 5,598

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 Jun 03, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1521 Description

The Local Interconnect Network (LIN) Bus consists of a single wire with a transmission rate of 10.417 Kbit/s. The serial data is transmitted over a LIN circuit between a master control module and other LIN devices within a particular subsystem. If serial data communication is lost between any of the LIN devices on the LIN bus network, the master control module will set a no communication code against the non-communicating LIN device. The Diagnostic Trouble Code (DTC) will set when a supervised periodic message to the Headlamp Control Module/Headlamp Leveling Control Module from the Left Headlamp has not been received.

OBDII Code U1521 - Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus - AutoCodes.com — U1521 Code - Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus

What does this mean?

What are the Possible Causes of the DTC U1521?

Faulty Left Headlamp
Left Headlamp harness is open or shorted
Left Headlamp circuit poor electrical connection
Faulty Headlamp Control Module/Headlamp Leveling Control Module

How to Fix the DTC U1521?

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 U1521 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 U1521 code?

Need more information on how to fix the U1521 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U1521 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U1521 Buick — Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus
U1521 Cadillac — Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus
U1521 Chevrolet — Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus
U1521 GMC — Headlamp Control Module/Headlamp Leveling Control Module Lost Communication With Left Headlamp On LIN Bus

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 U1521 Code

1. What are the common symptoms of OBDII code U1521?

- Common symptoms include the left headlamp not functioning properly, flickering headlamp, or dashboard warning light related to headlamp issues.

2. What does OBDII code U1521 indicate?

- This code indicates a communication problem between the headlamp control module or headlamp leveling control module and the left headlamp on the LIN bus network.

3. What are the possible causes of code U1521?

- Possible causes include a faulty headlamp control module, damaged wiring or connectors, a malfunctioning headlamp leveling control module, or a communication network issue.

4. How can I diagnose OBDII code U1521?

- Diagnosing this code involves checking the wiring and connectors for damage, testing the headlamp control module and headlamp leveling control module, and verifying communication on the LIN bus network.

5. How can I repair OBDII code U1521?

- Repair options may include replacing a faulty headlamp control module, fixing damaged wiring or connectors, replacing the headlamp leveling control module, or addressing any communication network issues.

6. Can I continue driving with OBDII code U1521?

- It is not recommended to drive with this code present, as it can affect the proper functioning of the left headlamp, potentially compromising visibility and safety.

7. Is OBDII code U1521 a serious issue?

- While this code may not affect the drivability of the vehicle, it is important to address it promptly to ensure the proper operation of the headlamp system.

8. Can a DIY enthusiast fix OBDII code U1521?

- Depending on the cause of the code, some repairs may be within reach of a skilled DIY enthusiast, such as checking and fixing wiring or replacing modules. However, complex diagnosis and repair may require professional assistance.

9. How much does it cost to repair OBDII code U1521?

- Repair costs can vary widely depending on the underlying issue and whether parts need to be replaced. It is recommended to obtain a diagnostic from a qualified technician for an accurate estimate.

10. Can weather conditions affect OBDII code U1521?

- Extreme weather conditions, such as water damage from flooding or exposure to excessive heat, can potentially contribute to the development of communication issues leading to code U1521.