FAULTBASE
Error CodesASKCars
© 2025 FAULTBASE
All rights reserved.
v2.0.0 • Production
ContactPrivacyImpressum
Home/Cars/Tesla/Model S/Plaid/Refresh (2021-present)/what does error code U0121 mean in my Tesla Model S Original (2012-2020)

what does error code U0121 mean in my Tesla Model S Original (2012-2020)

Tesla Model S Plaid/Refresh (2021-present)

Error Codes
Severity: highDifficulty: mediumError Code: U01212-3 hours
3 min read
509 words

⚠️ Safety Warning

This issue requires immediate attention. If you are not experienced with automotive repairs, consult a professional mechanic. Working on critical systems can be dangerous.

Problem Statement

Learn how to diagnose and fix U0121 ABS communication issue in Tesla Model S. Step-by-step guide with diagnostic procedures and repair instructions.

Error Code
U0121
Affected Component
Brakes
Estimated Time
2-3 hours

Safety Warnings

  • ⚠Disconnect the battery before working on electrical systems to prevent shorts and electric shock.

Symptoms

  • •Check engine light illuminated
  • •Loss of braking assistance or ABS functionality
  • •Inconsistent brake pedal feel
  • •Warning messages related to stability control or ABS
  • •Possible electrical system irregularities

Diagnostic Steps

  1. 1Scan the vehicle's onboard diagnostic system using an OBD-II scanner to confirm U0121 and check for any additional codes.
  2. 2Inspect the ABS module connections and wiring for damage, corrosion, or loose connections.
  3. 3Verify the condition of the vehicle’s battery and charging system, ensuring proper voltage levels.
  4. 4Check for any blown fuses related to the ABS or communication circuits.
  5. 5Perform a visual inspection of the CAN bus wiring to ensure there are no breaks or shorts.
  6. 6Use a multimeter to test the continuity of the ABS module's power and ground circuits.

Solution

Solution

1. Preparation

  • Gather tools and safety equipment.
  • Disconnect the vehicle's 12V battery to ensure safety while working on electrical components.

2. Inspect Wiring and Connections

  • Tools Required: Socket set, multimeter, OBD-II scanner
  • Sub-steps:
    • Locate the ABS module and inspect the wiring harness for damage or corrosion.
    • Disconnect the ABS module connector and clean the terminals with electrical contact cleaner.
    • Reconnect the ABS module and check for secure connections.

3. Check Battery and Fuses

  • Tools Required: Multimeter, fuse puller
  • Sub-steps:
    • Use a multimeter to measure the battery voltage; it should be around 12.6V or higher when fully charged.
    • Inspect the fuses related to the ABS and PCM circuits; replace any blown fuses with the appropriate amperage rated fuses.

4. Test CAN Bus Communication

  • Tools Required: OBD-II scanner, multimeter
  • Sub-steps:
    • Using the OBD-II scanner, check if the ABS module communicates with the PCM.
    • If communication is still lost, inspect the CAN bus wiring for continuity and shorts using a multimeter.

5. Reconnect Battery and Clear Codes

  • Tools Required: None
  • Sub-steps:
    • Reconnect the 12V battery.
    • Use the OBD-II scanner to clear any stored trouble codes.

Verification

After completing the repair, verify that the issue has been resolved:

  • ✓Test the affected component to ensure it functions correctly
  • ✓Check for any error codes or warning lights
  • ✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

  • •Follow the manufacturer's recommended maintenance schedule
  • •Address warning signs early before they develop into major issues
  • •Use quality parts and fluids recommended for your vehicle
  • •Keep detailed records of all repairs and maintenance

Tools & Equipment Required

  • •OBD-II scanner
  • •Multimeter
  • •Socket set
  • •Fuse puller

Parts Required

  • •ABS module (if faulty)
  • •Fuses (if blown)

Additional Information

Error Code
U0121
Affected Component
Brakes
Estimated Time
2-3 hours
Difficulty
medium
Severity
high
Tools Required
4 items
Parts Required
2 items

Related Faults

  1. why does my Tesla Model S have a hard clutch pedal

    Learn how to diagnose and fix a hard clutch pedal in Tesla Model S. Step-by-step guide with diagnostic procedures and repair instructions.

    Transmission5 symptoms

  2. how to fix transmission slipping in my Tesla Model S Plaid/Refresh (2021-present)

    Learn how to diagnose and fix transmission slipping in Tesla Model S Plaid (2021-present). Step-by-step guide with symptoms, diagnostics, and solutions.

    Transmission5 symptoms

  3. my Tesla Model S has a hard steering when cold what should I check

    Learn how to diagnose and fix hard steering issues in Tesla Model S. Step-by-step guide with symptoms, diagnostic steps, and repair instructions.

    Steering5 symptoms

  4. my Tesla Model S battery drains too quickly what should I check

    Learn how to diagnose and fix rapid battery drain in Tesla Model S. Step-by-step guide with diagnostic procedures and repair instructions.

    Electrical5 symptoms

  5. my Tesla Model S Plaid/Refresh (2021-present) has a hard brake pedal what should I check

    Learn how to diagnose and fix hard brake pedal issues in Tesla Model S Plaid (2021-present). Step-by-step guide with symptoms, diagnostic steps, and repair instructions.

    Brakes5 symptoms

  6. my Tesla Model S has a loud popping noise from the speakers what's going on

    Learn how to diagnose and fix loud popping noise from speakers in Tesla Model S. Step-by-step guide with diagnostic procedures and repair instructions.

    Electrical5 symptoms

Share this solution

Comments

Sign in to share your thoughts

Sign In

No comments yet

Be the first to share your thoughts

Back to Generation