What it means
The control module monitors the DC/DC converter temperature sensor B signal and sets this code when the signal is below the expected electrical range. This indicates a low circuit reading, which may not reflect the converter's actual temperature.
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 changes high-voltage battery power into lower-voltage power used by vehicle electrical systems. The control module monitors temperature sensor B’s signal and sets P0C3F when the circuit voltage is below its expected electrical range; a low signal can result from a short to ground or a failed sensor and does not prove the converter is actually cold. The converter may limit output if the temperature information is unreliable.
Common causes
Most likely first.
- Short to ground in the sensor circuit
- Faulty temperature sensor
- Poor connector connection
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
- Record freeze-frame data and inspect live data for sensor B to confirm the low reading and note the conditions when it occurred.
- With the vehicle powered down as directed by the manufacturer, inspect sensor B’s connector for moisture, corrosion, bent terminals, or a terminal touching ground.
- Check sensor B’s harness for rubbed-through insulation, pinching, or contact with grounded metal that could pull the signal low.
- Using the wiring diagram and manufacturer’s procedure, test the sensor B signal circuit for a short to ground and check circuit continuity.
- Test temperature sensor B against the manufacturer’s specification, then compare its response with sensor A if appropriate.
Common fixes
- Clean and secure sensor B’s connector or repair a terminal shorting to ground.
- Repair chafed sensor B wiring that is contacting ground.
- Replace sensor B if it produces a low signal with the circuit wiring intact.
- Clear the code and confirm sensor B’s signal returns to a plausible range.
Can I keep driving?
Avoid long trips and heavy electrical loads if hybrid operation or power is limited. If the vehicle shows a critical hybrid warning or loses substantial power, stop safely because the converter may reduce output 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.