P0A21 fault code: Motor Torque Sensor Circuit Intermittent High severity

P0A21 means “Motor Torque Sensor Circuit Intermittent” — a hybrid propulsion fault in the powertrain. If the car enters ready mode and drives normally, short trips are fine; do not ignore isolation warnings. Typical UK repair cost: £90–£3000 depending on the underlying cause.
HighSeverity
P0AxxHybrid Propulsion
£90–3000Typical UK repair cost
MOT fail riskif the warning light stays on

What does P0A21 mean?

P0A21 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P0Axx block, which covers hybrid propulsion. The stored description is “Motor Torque Sensor Circuit Intermittent”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed, which is why a short diagnosis pays for itself before replacing components.

Symptoms you may notice

  • Hybrid or EV warning light on the dash
  • Reduced electric range or the engine running constantly
  • Car refuses to enter ready mode

Most common causes

  1. Ageing high-voltage battery cells or balancing faults
  2. Cooling system faults for the battery pack
  3. 12V auxiliary battery failure (surprisingly common trigger)
  4. Isolation faults in high-voltage wiring

How to diagnose P0A21 yourself

  1. Test the 12V auxiliary battery first — a weak 12V battery causes many phantom hybrid codes
  2. Read hybrid battery block voltages with a capable scanner
  3. High-voltage repairs belong with a hybrid-qualified technician
Tools that read and clear P0A21

A basic code reader confirms the fault; a full-system scanner shows the live data you need for the steps above.

Will P0A21 fail an MOT?

Hybrid and EV warning lamps are inspected at MOT — an illuminated propulsion battery warning is a Major defect.

Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.

Typical UK repair costs

OutcomeTypical cost (parts + labour)
DIY: read code + basic checks£0 (scanner assumed)
Independent garage diagnosis£30–£60
Typical repair range for this fault£90–£3000
Main dealer equivalent£135–£5400

Costs are indicative UK ranges for independent garages in 2026. Main dealers typically charge 40–80% more.

Diagnose the symptom, then price the repair

Car diagnostic test cost UK (2026): scan vs actual diagnosis£40–£100 is typical for an independent first assessment — but a code read is not the same as finding the cause.
P0A00Motor Electronics Coolant Temperature Sensor Circuit P0A01Motor Electronics Coolant Temperature Sensor Circuit Range/Performance P0A02Motor Electronics Coolant Temperature Sensor Circuit Low P0A03Motor Electronics Coolant Temperature Sensor Circuit High P0A04Motor Electronics Coolant Temperature Sensor Circuit Intermittent P0A05Motor Electronics Coolant Pump Control Circuit/Open P0A06Motor Electronics Coolant Pump Control Circuit Low P0A07Motor Electronics Coolant Pump Control Circuit High

P0A21 — quick answers

Is it safe to drive with P0A21?

If the car enters ready mode and drives normally, short trips are fine; do not ignore isolation warnings.

Will P0A21 clear itself?

If the underlying fault stops occurring, most ECUs extinguish the light after around 40 healthy warm-up cycles — but the code stays stored as history. Fix the cause, clear it with a scanner, then confirm it stays away over a full drive cycle.

How much does it cost to fix P0A21 in the UK?

Typically £90–£3000 at an independent garage depending on which cause you confirm. Diagnosing it yourself with a scanner avoids a £30–£60 diagnostic fee and stops parts being replaced on guesswork.

Will P0A21 fail my MOT?

Hybrid and EV warning lamps are inspected at MOT — an illuminated propulsion battery warning is a Major defect.

Code definitions follow the SAE J2012 standard. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.