C121C: owner reports and bulletins
Got C121C on your scanner? Tell the mechanic your year, make, model and any symptoms and you'll get the likely cause and what to check first. Ask about this code.
What owners report to NHTSA
17 complaints filed with NHTSA mention C121C, 12 of them since 2015, across 10 different models. The component owners most often filed it under: power train.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| CHRYSLER TOWN AND COUNTRY | 4 | 2008, 2010 |
| JEEP WRANGLER | 4 | 2013, 2016, 2021, 2025 |
Manufacturer service bulletins that name C121C
13 technical service bulletins and manufacturer communications filed with NHTSA mention C121C, from 4 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- JEEP GLADIATOR (2021, 2022), bulletin 10212348: ESC (Electronic Stability Control) Lamp On, DTC C121C-00-TORQUE REQUEST SIGNAL DENIED
- MITSUBISHI ECLIPSE CROSS (2018), bulletin 10142734: This is a Technical Service Bulletin sent to dealers. It instructs dealers to reprogram the engine ECU with updated software to correct the issue, on certain vehicles, of MIL illumination with DTC P061A. During turbochar…
- CHRYSLER PACIFICA (2017), bulletin 10080001: "FLASH: 3.6L POWERTRAIN DIAGNOSTIC AND SYSTEM ENHANCEMENTS THIS BULLETIN INVOLVES REPROGRAMMING THE POWERTRAIN CONTROL MODULE (PCM) WITH THE LATEST AVAILABLE SOFTWARE. CUSTOMERS MAY EXPERIENCE A MALFUNCTION INDICATOR LAM…
- VOLKSWAGEN ROUTAN (2009, 2010), bulletin 10121189: Tech Tips: Routan equipped with 3.8 L or 4.0 L - Stumble/Jerk at low speeds or while stopping, C121C stored in the ABS module (sporadic)
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.