What it means
The DC/DC converter temperature sensor B circuit signal is higher than expected.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The DC/DC converter steps high-voltage battery power down for the vehicle’s lower-voltage electrical system. The control module monitors temperature sensor B’s signal and sets P0C40 when the circuit reading is above its expected electrical range; an open circuit or short to voltage can create a high signal even if the converter is not hot. The converter may restrict output when it cannot trust this temperature input.
Common causes
Most likely first.
- Open circuit in the sensor wiring
- Short to voltage in the sensor circuit
- Faulty temperature sensor
Symptoms
- Hybrid-system warning light may illuminate
- Reduced power or limited hybrid operation
- DC/DC converter may limit output to protect itself
How to diagnose it
- Save freeze-frame data and check live data for sensor B to confirm the high reading and identify when it occurs.
- With the vehicle powered down according to the manufacturer’s procedure, inspect sensor B’s connector for a loose terminal, corrosion, water, or a disconnected plug.
- Trace sensor B’s wiring for a broken conductor, pulled connection, damaged insulation, or contact with a voltage-carrying wire.
- Use the wiring diagram and manufacturer’s procedure to check sensor B circuit continuity and test for a short to voltage.
- Test sensor B’s resistance or signal response against the manufacturer’s specification and compare it with sensor A where applicable.
Common fixes
- Reconnect sensor B’s plug and repair loose or damaged terminals.
- Repair an open in sensor B’s wiring or a short to voltage.
- Replace temperature sensor B if it fails its specified test with wiring intact.
- Clear the code and verify the sensor B reading is plausible during operation.
Can I keep driving?
Keep trips short and avoid heavy electrical loads if hybrid operation or power is reduced. Stop safely if a critical hybrid warning or major power loss occurs, as converter output may be limited further.
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.