Here the torque sensor on the traction motor shaft delivers a signal that drops out or jumps for short moments instead of failing permanently. Such shaft sensors, as in the Honda patent with a sensor inside a hollow motor shaft, sit in an area with strong electromagnetic fields and vibration, so loose terminals, chafed wires and interference are the usual suspects. P0A21 sets when the control unit counts too many implausible signal changes. No manufacturer documents P0A21 publicly; CARB demands an approved drive motor monitor. Steady faults would show as P0A19 or P0A20. The warning may come and go.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
Symptoms
- Hybrid warning that appears and disappears
- Brief loss of electric assist
Most likely causes
- Loose or fretted terminal in the sensor connector
- Chafed sensor wiring that shorts briefly under vibration
- Damaged shield letting inverter noise into the signal
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0A21 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- A: Hybrid or air and fuel
- 21: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0A21?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0A21?
The most common causes are: loose or fretted terminal in the sensor connector; chafed sensor wiring that shorts briefly under vibration; damaged shield letting inverter noise into the signal.
Related codes
- P0A17Motor Torque Sensor Circuit
- P0A18Motor Torque Sensor Circuit Range/Performance
- P0A19Motor Torque Sensor Circuit Low
- P0A20Motor Torque Sensor Circuit High
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.