What it means
The ECM detects a circuit fault on the hybrid/ev battery pack coolant temperature sensor b circuit. Reading cannot be used reliably for control.
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 battery pack cooling system, and the vehicle control module uses its signal to manage battery cooling and charging. This code sets when the sensor B circuit has an electrical fault that makes its reading unreliable.
Common causes
Most likely first.
- Coolant temperature sensor B failed
- Damaged wiring or poor connector connection
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Save freeze-frame data and read battery coolant sensor data to see what the module reported when the circuit fault set.
- With the vehicle powered down according to the manufacturer's safety procedure, inspect sensor B's connector and accessible wiring for damage, coolant contamination, or a loose connection.
- Compare sensor B's reading with other battery coolant temperature data and ambient conditions to identify an implausible or missing signal.
- Check the sensor B circuit connections and continuity using the manufacturer's procedure, paying attention to connector contact quality.
- Test sensor B against the manufacturer's specification and replace it only if the wiring and connections are sound.
Common fixes
- Reconnect or clean a loose or contaminated sensor B connector, following the manufacturer's high-voltage safety procedure.
- Repair damaged wiring or poor connections in the sensor B circuit.
- Replace battery pack coolant temperature sensor B if it fails the specified test.
- Clear the fault and confirm sensor B data is plausible and the warning does not return.
Can I keep driving?
Because the vehicle may limit power or charging to protect the battery, avoid hard acceleration and long trips if reduced power is present. Stop safely if the vehicle warns of a battery temperature or hybrid system problem, and follow its instructions.
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.