U0121 Code - Lost Communication With Anti-Lock Brake System Control Module

Quick Answer

When a vehicle's onboard computer system detects the U0121 code, it means that there is a communication problem between the Engine Control Module (ECM) and the Anti-Lock Brake System Control Module (ABS). Common causes include Faulty ABS control module, Loose or corroded wiring connections, ECM software malfunction. 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

U0121 indicates Lost Communication With Anti-Lock Brake System Control Module .

Common causes

Common causes include Faulty ABS control module, Loose or corroded wiring connections, ECM software malfunction.

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.

• Description
• Common Causes
• Symptoms
• How To Fix
• Cost to Fix
• FAQs
• Comments
• Add Comment

Common Causes of U0121

Symptoms of U0121

How to Fix U0121

Cost to Fix U0121

Need more information about the U0121 code?

Need more information on how to fix the U0121 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0121 code diagnosed by a professional: Find a repair shop in your area

Code U0121 Information for Specific Makes

• U0121 Buick — Lost Communication With Electronic Brake Control Module
• U0121 Cadillac — Lost Communication With Electronic Brake Control Module
• U0121 Chevrolet — Lost Communication With Electronic Brake Control Module
• U0121 Chrysler — Lost Communication With Anti-Lock Brake System Module
• U0121 Dodge — Lost Communication With Anti-Lock Brake System Module
• U0121 Fiat — Lost Communication With Anti-Lock Brake System Module
• U0121 Ford — Lost Communication With The Anti-lock Brake System Control Module
• U0121 GMC — Lost Communication With Electronic Brake Control Module
• U0121 Honda — Lost Communication With Anti-Lock Brake System Control Module
• U0121 Hummer — Lost Communication With Electronic Brake Control Module
• U0121 Infiniti — Lost Communication With Anti-Lock Brake System Control Module
• U0121 Jeep — Lost Communication With Anti-Lock Brake System Module
• U0121 Lincoln — Lost Communication With The Anti-lock Brake System Control Module
• U0121 Mazda — Lost Communication With The Anti-lock Brake System Control Module
• U0121 Mercury — Lost Communication With The Anti-lock Brake System Control Module
• U0121 Nissan — Lost Communication With Anti-Lock Brake System Control Module
• U0121 Pontiac — Lost Communication With Electronic Brake Control Module
• U0121 RAM — Lost Communication With Anti-Lock Brake System Module
• U0121 Saturn — Lost Communication With Electronic Brake Control Module

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 U0121 Code

1. What are the common symptoms of OBDII code U0121 (Lost Communication With Anti-Lock Brake System Control Module)?

- Common symptoms include the ABS warning light illuminating on the dashboard, loss of anti-lock brake system functionality, and potential traction control issues.

2. What are the possible causes of OBDII code U0121?

- The code U0121 can be triggered by issues such as damaged wiring or connectors, a faulty ABS control module, a malfunctioning CAN bus communication system, or a problem with the power or ground circuit.

3. How can I diagnose the cause of OBDII code U0121?

- To diagnose the cause of U0121, it is recommended to perform a thorough inspection of the wiring and connectors related to the ABS control module, check for any loose connections, and use a diagnostic scan tool to analyze the communication between the modules.

4. Can driving with OBDII code U0121 pose any risks?

- Driving with code U0121 can be risky as it may result in the loss of important safety features provided by the anti-lock brake system. It is advised to address the issue promptly to ensure safe driving conditions.

5. What are some repair tips for resolving OBDII code U0121?

- Repair tips may include checking and repairing any damaged wiring, ensuring all connectors are securely plugged in, resetting the fault codes after repairs, and testing the vehicle to confirm the issue has been resolved.

6. Is it possible to reset OBDII code U0121 without fixing the underlying issue?

- While you can clear the code with a diagnostic scan tool, it is not recommended to reset the code without addressing the underlying problem. The issue may persist, potentially leading to safety concerns or further damage.

7. How much does it typically cost to repair OBDII code U0121?

- The cost of repairing U0121 can vary depending on the root cause of the issue, the extent of the repairs needed, and the labor rates in your area. It is advisable to consult with a professional mechanic for an accurate estimate.

8. Can OBDII code U0121 be triggered by a dead battery?

- Yes, a dead or disconnected battery can sometimes trigger U0121 due to the loss of power to the ABS control module. In such cases, resolving the battery issue may also resolve the communication problem.

9. Are there any common related codes that may accompany U0121?

- Yes, codes related to communication errors or faults in other control modules, such as the Engine Control Module (ECM) or Transmission Control Module (TCM), may sometimes accompany U0121 and provide additional diagnostic clues.

10. How urgent is it to address OBDII code U0121?

- It is important to address code U0121 promptly to ensure the proper functioning of the anti-lock brake system and maintain safe driving conditions. Ignoring the issue may compromise vehicle safety and lead to further complications.