Service manual info on Battery Temp Sensor
Here's some text straight outta the Service Manual which might help.
Or bring up even more questions... .
"The Battery Temperature Sensor (BTS) is attached
to the battery tray located under the battery.
"The BTS is used to determine the battery temperature
and control battery charging rate. This temperature
data, along with data from monitored line
voltage, is used by the PCM (ECM Diesel) to vary the
battery charging rate. System voltage will be higher
at colder temperatures and is gradually reduced at
warmer temperatures.
"The PCM sends 5 volts to the sensor and is
grounded through the sensor return line. As temperature
increases, resistance in the sensor decreases
and the detection voltage at the PCM increases.
The BTS is also used for OBD II diagnostics. Certain
faults and OBD II monitors are either enabled
or disabled, depending upon BTS input (for example,
disable purge and enable Leak Detection Pump
(LDP) and O2 sensor heater tests). Most OBD II
monitors are disabled below 20°F. "
aJ