P0CB9
Hybrid/EV Battery Temperature Sensor P Circuit Low.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- C
- AreaHybrid propulsion
- B9
- FaultThe specific fault in that area
What it means
P0CB9 means the hybrid or EV battery control unit has seen the signal from one of the traction battery temperature sensors (identified as sensor 'P') read too low, suggesting a short to ground or a very low resistance in that sensor circuit. Which physical sensor is 'P' depends on the vehicle and battery pack design. The control unit cannot trust the reading, so it may limit battery use to protect the pack.
Symptoms
- Hybrid or EV system warning light, or malfunction indicator lamp, on
- Reduced power or limited acceleration
- Reduced or unavailable electric-only driving or regenerative braking
- Battery cooling fan running constantly or at odd times
- Reduced charging rate or charging refused
- Inaccurate or erratic battery temperature reading on a scan tool
Possible causes
- Faulty battery temperature sensor reading falsely low (internal short or drift)likely
- Sensor signal wire shorted to ground or to another wire in the pack harnesslikely
- Damaged, corroded or wet connector or terminals at the sensor or battery control unitpossible
- Chafed or crushed wiring from impact, previous repair or pack servicingpossible
- Fault in the battery monitoring or control unit input circuitrare
- Real temperature far lower than expected, such as in extreme cold, combined with a sensor faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting battery temperatures, ambient temperature and whether other temperature sensor codes are present.
- Compare the live data from all battery temperature sensors with each other and with ambient temperature after the car has sat for several hours; look for one reading that is implausibly low or stuck.
- Check for any technical service information for the specific model about the location and numbering of sensor 'P'.
- Following the manufacturer's high-voltage safety procedure, which must be carried out by a suitably trained technician, visually inspect the accessible harness and connectors for damage, moisture, corrosion or pushed-back pins.
- With the system safely isolated, measure the sensor resistance and compare it with the manufacturer's specification at the current temperature.
- Check the signal wire for a short to ground and for continuity back to the control unit, and check the reference supply voltage where specified.
- Wiggle-test the harness and connectors while watching live data for sudden changes.
- If wiring and sensor test fine, check for a fault in the control unit using the manufacturer's diagnostic procedure.
How to fix
- Replace the faulty battery temperature sensor or the sensor assembly, as the pack design requires.
- Repair or replace damaged wiring that is shorted to ground, using the approved repair method.
- Clean, repair or replace corroded or damaged connectors and terminals, and fix any water ingress source.
- Replace the battery control unit only if testing proves that it is faulty, and carry out any required setup procedure.
- After repair, clear the code and road-test, then recheck live temperature data to confirm that the code does not return.
Can I keep driving?
The car can often be driven for a short time, but power may be limited and the battery may not be properly protected from overheating or cold. Have it checked soon, and stop driving if a red warning appears or the car loses drive.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.