AutoCodes – Generic – C0121

C0121 Code - Valve Relay Circuit

Quick Answer

The system relay is energized when the ignition is ON. Common causes include Faulty Electronic Brake Control Module (EBCM), Electronic Brake Control Module (EBCM) harness is open or shorted, Electronic Brake Control Module (EBCM) 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: C0121 indicates Valve Relay Circuit.
Common causes: Common causes include Faulty Electronic Brake Control Module (EBCM), Electronic Brake Control Module (EBCM) harness is open or shorted, Electronic Brake Control Module (EBCM) 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 16,452

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 May 06, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code C0121 Description

The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage. The Electronic Brake Control Module (EBCM) controls each solenoid valve by grounding the solenoid. The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes:
- Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events.
- Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.

OBDII Code C0121 - Valve Relay Circuit - AutoCodes.com — C0121 Code - Valve Relay Circuit

What does this mean?

What are the Possible Causes of the DTC C0121?

Faulty Electronic Brake Control Module (EBCM)
Electronic Brake Control Module (EBCM) harness is open or shorted
Electronic Brake Control Module (EBCM) circuit poor electrical connection

How to Fix the DTC C0121?

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 C0121 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 C0121 code?

Need more information on how to fix the C0121 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the C0121 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

C0121 Buick — Valve Relay Circuit
C0121 Cadillac — Valve Relay Circuit
C0121 Chevrolet — Valve Relay Circuit
C0121 GMC — Valve Relay Circuit
C0121 Subaru — Front Outlet Valve Left

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 C0121 Code

1. What are common symptoms of OBDII code C0121 (Valve Relay Circuit)?

- Common symptoms include the ABS warning light illuminating on the dashboard, difficulty braking, and potential loss of ABS functionality.

2. What are possible causes of OBDII code C0121 (Valve Relay Circuit)?

- Possible causes include a faulty ABS relay, damaged wiring or connectors in the ABS system, or a malfunctioning ABS control module.

3. How can I diagnose the issue related to OBDII code C0121 (Valve Relay Circuit)?

- Diagnosis typically involves using a scan tool to retrieve the code, checking the ABS system's wiring and connectors for damage, and testing the ABS relay and control module for proper functioning.

4. Can I still drive my vehicle with OBDII code C0121 (Valve Relay Circuit) present?

- It is not recommended to drive the vehicle with this code present, as it may affect the ABS system's operation and compromise braking performance.

5. How can I repair OBDII code C0121 (Valve Relay Circuit) myself?

- DIY repair options include checking and replacing any damaged wiring or connectors, testing and replacing the ABS relay if needed, or resetting the ABS system using a scan tool.

6. Is it necessary to visit a mechanic for OBDII code C0121 (Valve Relay Circuit)?

- While DIY repairs are possible, it is recommended to visit a mechanic for a thorough diagnosis and repair of the ABS system to ensure proper functionality and safety.

7. Are there any safety precautions to take when dealing with OBDII code C0121 (Valve Relay Circuit)?

- Safety precautions include disconnecting the vehicle's battery before working on the ABS system, using proper tools and equipment, and following repair procedures outlined in the vehicle's service manual.

8. How much does it cost to repair OBDII code C0121 (Valve Relay Circuit) at a repair shop?

- Repair costs can vary depending on the extent of the issue, parts needed for replacement, and labor rates at the repair shop, but it may range from $200 to $500 or more.

9. Can OBDII code C0121 (Valve Relay Circuit) cause other problems in the vehicle?

- If left unresolved, this code can potentially lead to ABS system failure, compromised braking performance, and safety hazards while driving.

10. How often does OBDII code C0121 (Valve Relay Circuit) occur in vehicles?

- This code can occur in vehicles with ABS systems, particularly in older vehicles or those exposed to harsh driving conditions, but the frequency may vary depending on individual vehicle usage and maintenance.