Lost Communication With Anti-Lock Brake System Module
What does U0121 mean?
The U0121 code means the vehicle's onboard diagnostic system has detected: Lost Communication With Anti-Lock Brake System Module. This is a moderate severity code.
Common Symptoms
- ABS warning light illuminated
- Check Engine Light may be on
- ABS system inoperative
- Traction control and stability control disabled
- Normal braking still works
Probable Causes (Ranked by Likelihood)
- Failed ABS module Very High
- CAN bus wiring fault to ABS module High
- Corroded ABS module connector Moderate
- ABS module power supply loss Moderate
Step-by-Step Diagnostic Procedure
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Check ABS module power and ground circuits
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Inspect ABS module connector for corrosion -- common due to low mounting position
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Check CAN bus wiring to ABS module
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Verify ABS pump motor operates when commanded
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Replace ABS module if communication cannot be restored
Frequently Asked Questions
Can I drive with code U0121?
Drive short distances only. Lost communication codes indicate a module has stopped communicating on the vehicle network. The affected system may not function correctly.
What causes U0121?
The most common cause is a failed module or a wiring issue in the CAN bus network. Failed ABS module is the most likely cause. Power supply, ground, and connector issues should be checked before replacing any module.
Is U0121 expensive to fix?
Repair costs range from $200 - $1200 (parts and labor). Wiring repairs are on the lower end, while module replacement is on the higher end. The module may also need to be programmed after replacement.