Battery Temperature Sensor

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Purpose

A battery temperature sensor provides data indicating battery temperature to a control module. In hybrid vehicles, the data is used to activate the battery cooling system, usually by activating cooling fans. 

In some hybrid vehicles, the data may also cause the control module to disconnect the high voltage hybrid battery, should battery temperature exceed a specified maximum value. 

In the Chevrolet Volt and Cadillac ELR, sensor data is also used to activate a heating system that warms the battery if temperature drops below a specified value. In the few gasoline and diesel powered SUVs and light trucks that employ a battery temperature sensor, data from the sensor is used to adjust the rate of battery charge to avoid overheating.

Location

Multiple battery temperature sensors are used in hybrid vehicles. Toyota hybrids have three to five sensors located either on top of or underneath the high voltage hybrid battery pack. 

Other hybrids, including Honda Civics, use sensors located on individual cells, integral with the cell. The Chevrolet Volt and Cadillac ELR use 16 sensors that are integral to the hybrid battery pack.

In those gasoline or diesel powered light trucks and SUVs that use a battery temperature sensor, chiefly Dodge, Ram, and Jeep vehicles, a single sensor is located under the 12 volt battery, spring loaded to push it against the bottom of the battery case.

Operation

Battery temperature sensors are thermistors: sensors that change electrical resistance as the sensor’s temperature changes. The sensor receives a specific voltage, usually 5 volts, from the control module. 

Because the sensor is located on or near the battery, its temperature reflects battery temper-ature. As battery temperature – and, consequently, sensor temperature – increases, resistance to current through the sensor decreases and the voltage signal increases.

Though battery temperature sensors in many vehicles change resistance proportionally to temperature change, in some hybrid vehicles the battery temperature sensors change resistance only when a specific temperature is reached. These sensors function as temperature sensitive switches.

Drivability Symptoms

A warning light specific to the hybrid system may appear on the instrument panel of hybrid vehicles and the instrument panel Malfunction Indicator Lamp (MIL) may also illuminate. In gasoline and diesel powered light trucks equipped with the sensor, illumination of the MIL is the only symptom.

Inspection, Test, and Diagnosis

All vehicles equipped with a battery temperature sensor employ Second Generation On-Board Diagnostics (OBD2). 

In hybrid vehicles, diagnostic codes P0A9C, P0A9D, and P0A9E indicate battery temperature sensor malfunction for specific sensors. P0AC7, P0AC8, P0ACC, P0ACCD, and P0ACE indicate an abnormally low or high temperature, which may also indicate a fault in the sensor electrical circuit. These are “generic” codes shared by all vehicle manufacturers.

Individual manufacturers may also adopt “enhanced” codes unique to the specific vehicle manufacturer that further refine the diagnosis. Generic codes may be retrieved with any suitable Scan Tool that is new enough (or sufficiently updated) to include hybrid codes. Retrieval of enhanced codes requires a Scan Tool with that manufacturer specific capability.

In gasoline or diesel powered light trucks or SUVs employing a battery temperature sensor, generic code P0514 indicates a sensor failure and P0515 through P0517 indicate battery temperature readings out of the expected range, usually a short or open in the sensor circuit.

Reprogramming

Replacement of a battery temperature sensor does not require reprogramming. However, Chrysler issued a technical service bulletin for specific production numbers of the 2006 Ram trucks powered by the 5.9 liter Cummins engine recommending reprogramming the engine control module to revise logic employed to set the P0514 code.

Repair/Replacement

The battery temperature sensor in hybrid vehicles is not available as a separate component. Consequently, failure of a battery temperature sensor requires replacement of the high voltage hybrid battery.

In those gasoline or diesel powered vehicles equipped with a battery temperature sensor, the sensor can be replaced. To do so, the battery is removed and the sensor is gently pried from the battery tray and the electrical connector disconnected. The replacement sensor, once connected, snaps into the tray.

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