Powertrain, generic (extended)

P2B21 Hybrid/EV Electronics Coolant Temperature Sensor B Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Sensor B element drifted out of its characteristic curve
Air pocket around the sensor after coolant service or a leak
Corroded or loose terminals adding resistance to the signal
Controller calibration that needs an update

Symptoms

  • Hybrid system warning, often only after a cold start
  • Cooling pump or fan behaviour that does not match conditions
  • Occasionally limited electric power

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–450
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hybrid electronics coolant temp sensor bwiring harnesshybrid control module

Related codes

P2B20P2B22P2B23P2B25P0CEFP2D2A

References: law.cornell.edu, ntn-snr.com, gsi.ext.gm.com.