Battery Temperature Sensor: Operation

The PCM uses the temperature of the battery area to control the charge system voltage. This temperature, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. The system voltage is higher at cold temperatures and is gradually reduced as temperature around the battery increases.

For vehicles with 1.6L engine, there is no physical battery temp sensor in place to detect battery temp. Rather, an algorithm built in PCM is employed to predict battery temp using inlet air temp, vehicle speed, and coolant temp, among other signals. The PCM maintains the optimal output of the generator by monitoring battery voltage and controlling it to a range of 13.5 - 14.7 volts based on battery temperature. The system target voltage is 13.5 - 14.7 volts. However the actual voltage go below this during heavy electrical loads and generator speeds. Also the actual voltage can be lower than the target voltage between the battery and the battery voltage sense circuit, approximately 0.2 - 0.3 volts.

The battery temperature sensor is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled depending upon the battery temperature sensor input (example: disable purge and EGR, enable LDP). Most OBD II monitors are disabled below 20°F.