What it means
The vehicle hybrid control module detects a circuit 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 reports the temperature of the hybrid or EV power electronics cooling loop to the hybrid control module. P2B20 sets when the module detects an electrical fault in sensor B's circuit, so it may not be able to rely on that reading to protect the electronics from overheating.
Common causes
Most likely first.
- Sensor failed
- Wiring or connector fault
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-system codes to see when the sensor B circuit fault appeared and whether power was reduced.
- With the vehicle safely powered down according to its instructions, visually inspect sensor B's connector and accessible wiring along the power electronics cooling loop for damage, moisture, corrosion, or loose fit.
- Check live data for the sensor B temperature reading and compare it with other available coolant temperature readings when the vehicle is cold and during operation; look for an implausible or missing value.
- Check the sensor B circuit and connector for continuity, shorts, or poor connections using the manufacturer's wiring information and test method.
- Test sensor B against the manufacturer's specification and inspect its seating in the power electronics cooling loop before replacing parts.
Common fixes
- Reconnect and secure the sensor B connector if it is loose.
- Repair damaged or corroded wiring in the sensor B circuit.
- Replace coolant temperature sensor B if it fails testing against the manufacturer's specification.
- Refill and bleed the affected cooling loop as required after sensor removal, then confirm the reading and warning status.
Can I keep driving?
Because this fault can prevent the vehicle from monitoring the power electronics cooling loop correctly, follow any reduced-power warning and avoid demanding acceleration or extended driving. Stop safely if a cooling warning appears or power drops further, and have the hybrid system checked promptly.
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.