What it means
The vehicle hybrid control module detects a range/performance fault on the coolant temperature sensor B that monitors the power electronics cooling loop.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Coolant temperature sensor B measures the temperature of the hybrid or EV power electronics cooling loop for the hybrid control module. P2B21 sets when the reported temperature is outside the expected range or does not respond plausibly to operating conditions, which can happen if the sensor has drifted or is not seated correctly.
Common causes
Most likely first.
- Sensor characteristic drifted
- Sensor mounting displaced
- Sensor element aged beyond calibration window
Symptoms
- Hybrid-system or powertrain warning light
- Reduced hybrid or electric drive power
- Cooling-system warning
How to diagnose it
- Read freeze-frame data and related hybrid codes, noting the reported sensor B temperature and vehicle operating state when the range/performance fault set.
- Compare live sensor B temperature with other available coolant temperature readings when the vehicle is cold and as it warms; look for an implausible offset or lack of change.
- With the vehicle safely powered down according to its instructions, inspect sensor B's seating and connector, then check accessible wiring for damage, moisture, corrosion, or looseness.
- Check the power electronics cooling loop for signs of poor circulation or an abnormal temperature condition that could make a valid sensor reading appear unexpected.
- Test sensor B response and its circuit using the manufacturer's method and specification to distinguish a drifting sensor from a wiring or cooling-loop problem.
Common fixes
- Reseat and secure coolant temperature sensor B if it is displaced.
- Repair damaged, corroded, or loose connections in the sensor B circuit.
- Replace sensor B if its temperature response is outside the manufacturer's specification.
- Correct a confirmed cooling-loop circulation or temperature problem, then verify sensor readings and warning status.
Can I keep driving?
Reduced hybrid or electric drive power may be intended to protect the power electronics, so avoid hard acceleration and prolonged driving while the warning is present. Stop safely if a cooling warning appears or power falls further, and arrange prompt diagnosis because an inaccurate temperature reading can delay protection from overheating.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.