OBD Guide
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C121C

Torque Request Signal Denied

C121C is an OBD-II diagnostic trouble code meaning: Torque Request Signal Denied. Common causes: problems with the can bus, malfunction of sensors (mass air flow sensor, accelerator pedal position sensor). Estimated repair cost: $56–167.

Severity
⚠️ Medium
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$56–167 (est.)

Symptoms

  • Reduced engine power
  • Unstable engine operation
  • Switching to emergency mode
  • Check Engine light comes on

Causes

  • Problems with the CAN bus
  • Malfunction of sensors (mass air flow sensor, accelerator pedal position sensor)
  • Software failures in the ECU
  • Wiring harness damage
  • Contact corrosion

How to Fix

  1. Check the CAN bus for open circuit and short circuit
  2. Diagnose torque-related sensors (mass air flow sensor, accelerator pedal position sensor)
  3. Check the ECU software for errors
  4. Inspect the wiring harness for damage
  5. Clean or replace oxidized contacts

Related codes

P0121P0122P2135

FAQ

What does the C121C code mean?

C121C is an OBD-II diagnostic trouble code that indicates: Torque Request Signal Denied

What causes a C121C error code?

The most common causes of C121C include: Problems with the CAN bus; Malfunction of sensors (mass air flow sensor, accelerator pedal position sensor); Software failures in the ECU; Wiring harness damage.

How do I fix a C121C diagnostic trouble code?

To fix C121C: Check the CAN bus for open circuit and short circuit. Diagnose torque-related sensors (mass air flow sensor, accelerator pedal position sensor). Check the ECU software for errors. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with C121C?

Limited driving only, diagnose soon

How much does it cost to fix C121C?

The estimated repair cost for C121C is $56–167. Actual cost depends on your vehicle, location, and labor rates.

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