P0C85
Hybrid/EV Battery Temperature Sensor H Circuit Intermittent/Erratic.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- C
- AreaHybrid propulsion
- 85
- FaultThe specific fault in that area
What it means
P0C85 is a generic powertrain code meaning the control unit has detected an intermittent or erratic signal from the hybrid or EV battery temperature sensor designated 'H'. The battery management system saw readings that jumped, dropped out or did not follow a plausible temperature change. Which physical sensor 'H' refers to depends on the vehicle and battery pack design, so check the manufacturer's documentation.
Symptoms
- Hybrid or EV system warning light on the dashboard
- Reduced power or the car going into a limited performance mode
- Reduced or unavailable electric assist or regeneration
- Battery cooling fan running constantly or behaving oddly
- Reduced charging rate or charging that stops unexpectedly
- Fluctuating battery temperature reading on a scan tool
Possible causes
- Loose, corroded or damaged connector at the battery temperature sensor or battery management modulelikely
- Damaged, chafed or intermittently open-circuit wiring in the sensor harnesslikely
- Faulty battery temperature sensor giving erratic readingspossible
- Moisture or contamination in the battery pack connectors or sensor circuitpossible
- Poor sensor reference or ground connection affecting the signalpossible
- Fault within the battery management module or its internal sensor inputrare
How to diagnose
- Read all stored and pending codes and note freeze frame data, including battery temperatures and state of charge when the fault set
- Check for related codes on other battery temperature sensors, the cooling system or the battery management module, as a pattern can point to a shared wiring or module fault
- Watch live data for all battery temperature sensors and compare sensor H against the others; look for sudden jumps or dropouts
- Carry out a visual inspection of accessible wiring and connectors for chafing, corrosion, water ingress or looseness, following the manufacturer's high-voltage safety procedure
- With the sensor data live, gently wiggle the harness and connectors to see if the reading becomes erratic
- Test the sensor circuit resistance, continuity and reference and ground against manufacturer specifications; only trained staff should work on high-voltage battery components
- Check for technical service bulletins or software updates for the specific model, as the sensor location and test values vary between vehicles
How to fix
- Clean, reseat or replace faulty connectors and terminals in the sensor circuit
- Repair or replace damaged wiring in the sensor harness
- Replace the battery temperature sensor if it tests faulty, following the manufacturer's procedure
- Dry out and resolve any moisture ingress, and fix the cause of the leak
- Replace or update the battery management module only if confirmed faulty or if an outdated calibration is a known cause for that model
Can I keep driving?
The car may be drivable, but the system may restrict power or charging because it cannot monitor battery temperature reliably. Have it checked soon, and stop driving if warnings escalate, there is a burning smell or the battery overheats.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.