P2B21Hybrid/EV Electronics Coolant Temperature Sensor B Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Here sensor B delivers a voltage inside its electrical window, yet the temperature it reports does not fit the rest of the vehicle: it may stay flat while the electronics warm up, or disagree with other temperatures after the car has stood for hours. No manufacturer publishes the set condition of P2B21. NTN-SNR names it a deviation or malfunction of the sensor B signal. For sensor A, GM's 2019 HPC2 table runs such a test once per key cycle after a long rest and checks the reading against outside air, transmission fluid and the refrigerant high side (limits 27–28 °C, 8 s in 10 s, Type B as P0CEF). Typical causes are a drifting element, trapped air at the sensor tip or corroded contacts. Hard electrical faults go to P2B22 and P2B23, the A/B comparison to P2D2A.
- What you may notice
- Hybrid system warning, often only after a cold start
- Cooling pump or fan behaviour that does not match conditions
- Occasionally limited electric power
- Likely causes
- LikelySensor B element drifted out of its characteristic curve
- PossibleAir pocket around the sensor after coolant service or a leak
- PossibleCorroded or loose terminals adding resistance to the signal
- RareController calibration that needs an update
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €40 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.