Open circuit or high resistance in the sensor signal or return wiring; Corroded, loose or damaged connector at the sensor or battery control unit; Failed battery temperature sensor (open internally); Signal wire shorted to a voltage supply; Damage to the sensor harness inside the battery pack, for example from previous repair or impact; Fault in the battery control unit or its sensor input circuit; Outdated control unit software where the manufacturer has documented a fix.

P0C90

Hybrid/EV Battery Temperature Sensor J 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
90: FaultThe specific fault in that area

What it means

P0C90 is a generic powertrain code meaning the hybrid or EV battery control unit has seen a signal voltage that is too high from the battery temperature sensor designated 'J'. A high voltage on a typical thermistor circuit usually reads as an extremely cold temperature, so it often points to an open circuit, a poor connection or a failed sensor. Which physical sensor 'J' refers to varies by model and battery design.

Symptoms

Hybrid system, check engine or battery warning light on
Reduced power or limited electric assist or EV range
Reduced or stopped battery charging and regeneration
Cooling fan for the battery running at high speed or behaving oddly
Car going into a limp mode or failing to enter ready mode
Other battery temperature or battery module codes stored alongside

Possible causes

Open circuit or high resistance in the sensor signal or return wiringlikely
Corroded, loose or damaged connector at the sensor or battery control unitlikely
Failed battery temperature sensor (open internally)likely
Signal wire shorted to a voltage supplypossible
Damage to the sensor harness inside the battery pack, for example from previous repair or impactpossible
Fault in the battery control unit or its sensor input circuitrare
Outdated control unit software where the manufacturer has documented a fixrare

How to diagnose

Read all stored and pending codes and note freeze frame data, including battery temperatures and when the fault set
Check for related codes on other temperature sensors or the battery control unit, as shared wiring or supply faults can affect several
Compare live data for sensor J against the other battery temperature readings; an implausibly low or fixed value suggests an open circuit
Visually inspect the accessible wiring and connectors for damage, corrosion, water ingress or signs of past repair
Follow the manufacturer's high voltage safety procedure before touching any battery pack connectors or components, and only work on them if trained and qualified
With the system safely isolated, check the sensor resistance against the specification for that model and temperature
Test the signal, reference and return wires for continuity, short to voltage and short to earth using the wiring diagram
Check for applicable software updates or technical bulletins for that model

How to fix

Repair or replace the damaged wiring section, ensuring correct routing and securing
Clean, reseat or replace corroded or damaged connectors and terminals
Replace the faulty battery temperature sensor or sensor harness as specified for the model
Repair any short to voltage in the circuit and recheck the readings
Replace or reprogram the battery control unit only after the wiring and sensor are proven good and the manufacturer procedure confirms it
Apply a manufacturer software update if one is documented for this fault

Can I keep driving?

Medium severity

The car may be driveable, but the system may limit power and charging because it cannot monitor battery temperature properly. Have it checked soon, and stop driving if warnings escalate, the battery overheats or the car loses power.

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