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U0121
System
Network (CAN Bus)
Scanner som krävs
Full-system scanner (engine, ABS, SRS, transmission, service resets)

Lost Communication with ABS Control Module

Understand U0121, common causes, and the right TOPDON scanner to diagnose it.

ABS module not communicating — ABS, stability control, and sometimes cruise may be disabled.

Vanliga symptom

  • ABS light on
  • Traction control off
  • C-codes may accompany

Typiska orsaker

  • ABS module failure
  • Wheel speed sensor wiring damaging comm
  • Low voltage
  • Blown ABS fuse

Vilken scanner behöver du?

Full-system scanner (engine, ABS, SRS, transmission, service resets)

Använd live-data och freeze frame innan du byter delar. ABS-, SRS- och U-koder kräver oftast en fullsystems-scanner.

Diagnostiktips

  • Spara freeze frame när koden först sätts
  • Rensa koden först efter att orsaken är åtgärdad
  • Kontrollera relaterade väntande koder
  • Verifiera batterispänning över 12,4 V innan du misstänker sensorer

Rekommenderade TOPDON-scannrar

Vanliga frågor

What does U0121 mean?
U0121 indicates lost communication with abs control module. ABS module not communicating — ABS, stability control, and sometimes cruise may be disabled.
Can I diagnose U0121 with a basic code reader?
U0121 may set in the engine module, but related diagnostics often benefit from an enhanced or full-system scanner with live data and freeze frame.
Which TOPDON scanner do I need for U0121?
Full-system scanner (engine, ABS, SRS, transmission, service resets) See recommended tools on this page.
Is it safe to drive with U0121?
It depends on the code and symptoms. Flashing check engine lights and misfire codes should be addressed immediately. Consult a professional if unsure.