U0121 on TOYOTA RAV4
Lost Communication With Anti-Lock Brake System (ABS) Control Module A
Methodology: Reviewed against the SAE J2012 generic DTC definition and NHTSA owner-complaint patterns, then scoped to Toyota Rav4 context without treating complaints as confirmed diagnoses.
Sources: SAE/OBD-II definitions, manufacturer service information, and public reliability reports (including NHTSA where applicable).
- SAE J2012 Diagnostic Trouble Code Definitions — Generic diagnostic trouble code definition reference for U0121.
- NHTSA recalls, complaints, and manufacturer communications — Used to check public owner complaint context, recall status, and safety-related manufacturer communications by VIN or vehicle.
Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.
What U0121 Means on Your TOYOTA RAV4
U0121 is a diagnostic trouble code indicating: Lost Communication With Anti-Lock Brake System (ABS) Control Module A. This code relates to the vehicle network, module communication, or data bus system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.
Real TOYOTA RAV4 Owner Reports
Source: NHTSA Complaints Database
"Steering froze up while leaving my driveway and p/s light came on. shut engine off and back on, but did not resolve. i recall at least one other time that steering locked up temporarily while at a stop. took to dealership for diagnostic as manual recommends. diagnostic shows dtcs u0105 and u0121."
"Heard abnormal mechanical rattle from the front end going over rough streets in san francisco. took vehicle in suspecting suspension issue to capitol toyota of san jose."
All reports filed by vehicle owners directly with the U.S. Department of Transportation.
📊 Complaint Trend by Model Year
Common Causes on TOYOTA RAV4
Based on NHTSA complaint component analysis for this vehicle.
What To Do Next
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1
Check for recalls on YOUR VIN
Go to nhtsa.gov/recalls and enter your VIN. If your vehicle is covered, repairs are free.
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2
Get a proper diagnosis
A code alone doesn't tell you the exact failed part. A diagnostic at a shop ($50–$150) pinpoints the root cause before you spend money on parts.
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3
Compare repair quotes
Get 2–3 quotes. Dealer vs. independent shop prices often differ 30–50% for the same repair.