P0C8B
Hybrid/EV Battery Temperature Sensor I Circuit High.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- C
- AreaHybrid propulsion
- 8B
- FaultThe specific fault in that area
What it means
P0C8B means the hybrid or EV battery control unit has seen the signal from battery temperature sensor 'I' sit higher than its expected voltage range. This usually points to an open circuit, a short to voltage or a faulty sensor. Which physical sensor is 'I' and where it sits in the pack depends on the model, so check the manufacturer's information for the vehicle.
Symptoms
- Hybrid or EV system warning light, or malfunction indicator lamp, on
- Reduced power or limp-home mode
- Reduced or disabled battery charging and regeneration
- Battery cooling fan running constantly or behaving erratically
- Reduced electric range or the engine running more often on a hybrid
- Car refusing to enter Ready mode in some cases
Possible causes
- Open circuit or high resistance in the sensor wiring or connector, such as corrosion, a loose terminal or a pushed-out pinlikely
- Faulty battery temperature sensor (internal open circuit or drift)likely
- Short to a voltage supply in the sensor signal wirepossible
- Damaged or loose sensor connection at the battery pack or monitoring module, for example after previous repair work or impact damagepossible
- Fault in the battery monitoring unit or control module, including its sensor supply or input circuitrare
- Moisture or coolant ingress in the pack harness or connectorrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, and note any other battery temperature or cell monitoring codes.
- Check the live data for sensor I against the other battery temperature sensors; a value stuck at an extreme or far from the others points to a sensor or circuit fault.
- Check for manufacturer service bulletins or known issues for this model and the sensor in question.
- Visually inspect accessible wiring and connectors for damage, corrosion, moisture, loose terminals or signs of previous repair work. Only work on high-voltage components if you are qualified and have followed the manufacturer's isolation procedure.
- With the system safely isolated, check the sensor's resistance against the manufacturer's specification at a known temperature.
- Check the sensor circuit for continuity, short to voltage and short to earth, and check the reference supply and earth at the connector.
- Wiggle-test the harness and connector while watching live data for sudden jumps in the reading.
- If the wiring and sensor test good, check the monitoring unit's inputs and power and earth supplies as per the manufacturer's procedure.
How to fix
- Repair or replace damaged wiring, terminals or connectors in the sensor circuit.
- Clean and refit corroded or loose connectors, and fix the source of any moisture ingress.
- Replace the faulty battery temperature sensor or sensor harness as the manufacturer specifies, which may involve the battery pack or a sub-assembly.
- Repair any short to voltage found in the signal wire.
- If the monitoring module is confirmed faulty, replace it, or update its software where the manufacturer lists that as the fix, then clear the code and road test.
Can I keep driving?
The car may be driveable, often with reduced power, but the battery cannot be monitored properly so fix it soon. Stop driving and get it checked if warnings escalate, the power drops sharply, or you notice a burning smell, unusual heat or a pack fault message.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.