Damaged, corroded or loose wiring or connector at the battery temperature sensor circuit; Faulty battery temperature sensor (open or short circuit, or drifted reading); Poor connection or fault in the sensor harness inside the battery pack or at the monitoring module; Water or coolant ingress or contamination affecting the sensor circuit; Fault in the battery monitoring unit or battery control module; Outdated or faulty control unit software where the manufacturer has issued a known update for this fault.

P0C81

Hybrid/EV Battery Temperature Sensor H Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
C: AreaHybrid propulsion
81: FaultThe specific fault in that area

What it means

P0C81 is a generic powertrain code meaning the hybrid or EV battery control unit has found a fault in the circuit of temperature sensor 'H' in the traction battery. The unit saw a signal outside the expected range, an implausible reading, or a reading that disagreed with neighbouring sensors. Which physical sensor is 'H' depends on the make, model and battery pack design.

Symptoms

Hybrid or EV system warning light or malfunction indicator lamp on
Reduced power or limited electric assist
Reduced electric-only range or reduced charging rate
Battery cooling fan running constantly or at an odd speed
Car going into limp mode or refusing to enter Ready mode
Charging stopping early or not starting

Possible causes

Damaged, corroded or loose wiring or connector at the battery temperature sensor circuitlikely
Faulty battery temperature sensor (open or short circuit, or drifted reading)likely
Poor connection or fault in the sensor harness inside the battery pack or at the monitoring modulepossible
Water or coolant ingress or contamination affecting the sensor circuitpossible
Fault in the battery monitoring unit or battery control modulerare
Outdated or faulty control unit software where the manufacturer has issued a known update for this faultrare

How to diagnose

Read all stored and pending codes and note any other battery temperature, cooling or voltage codes, as these point to a shared cause
Review freeze frame data and check how often and under what conditions the fault set
Compare live data for all battery temperature sensors and look for 'H' reading wildly different from the others at a cold start
Check for relevant technical service bulletins and software updates for the specific model
Visually inspect accessible wiring, connectors and the battery cooling ducts for damage, corrosion, moisture or blockage
Check the sensor circuit for continuity, short to earth or short to supply, and resistance against the manufacturer's specification, following high-voltage safety procedures
Check the sensor's resistance against temperature specification if it is accessible and serviceable
Only a suitably trained technician should open or work on the high-voltage battery pack

How to fix

Repair or replace damaged wiring or connectors in the sensor circuit
Replace the faulty temperature sensor or sensor harness, as the pack design allows
Clean and dry corroded connections, and fix the source of any moisture ingress
Clear blocked battery cooling ducts or filters if they contribute to the temperature fault
Update the control unit software if a relevant update exists for the fault
Replace the battery monitoring module only after the wiring and sensor have been proven good

Can I keep driving?

Medium severity

The car can often be driven for a short time, but power and charging may be limited and the battery is not being monitored properly. Get it checked soon, and stop driving if a red hybrid or battery warning appears or the car loses power.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.