P2B20: Hybrid/EV Electronics Coolant Temperature Sensor B Circuit
What to do
Drivable — expect reduced power or extra fan noise while the system protects electronics it cannot see. Check the electronics cooling loop's level first (it is separate from any engine coolant), and have the sensor verified against its neighbours rather than replaced on suspicion. Do not ignore it: this loop guards components whose replacement cost makes the sensor a rounding error.
What this code means
Hybrid/EV electronics coolant temperature sensor B's circuit has a fault.
The power electronics have their own cooling circuit, and this sensor is one of its thermometers. An inverter switching hundreds of amps makes real heat in a small package, and semiconductors fail fast above their limits — so hybrids and EVs run a dedicated low-temperature loop for the electronics, separate from any engine cooling, with its own pump and its own sensors. The letters name multiple measuring points around that loop.
Losing a thermometer forces the system to be pessimistic. The module cannot run the electronics close to their limits when it cannot see the temperature, so expect derated power, a louder-than-usual pump or fan running as a precaution, or reduced charging — protection, not failure.
The sensor is cheap and its neighbours are not, which decides the checking order. Verify the reading against a second sensor in the loop before trusting it; a sensor reading plausible-but-wrong is exactly how a healthy inverter gets derated — or an overheating one gets missed. And check the coolant level first of all, because a low loop uncovers sensors and reads strange before anything is actually broken.
Likely causes
Start here
- Faulty inverter coolant temperature sensor · specialist
- Corroded or loose connector · specialist
Less common
- Low inverter coolant level · easy
- Coolant leak into the sensor connector · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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