BCM Code F12 - A/C Low Side Temperature Sensor Circuit: Notes
NOTE:
If this code is not displayed during second pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. See NOTE ON INTERMITTENTS.
A/C low side temperature sensor uses a thermistor to control signal voltage to BCM. BCM applies and monitors voltage on circuit No. 731 to sensor. When sensor is cold, its resistance is high; therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and signal voltage is lowered through sensor ground circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).
BCM Code F12 will set if signal voltage indicates an open circuit, temperature less than -29°F (-34°C), or shorted circuit, temperature greater than 189°F (87°C). These conditions can be observed in BCM data display (parameter P.2.8) as a reading outside range of -29°F to 189°F(-34°C to 87°C).
NOTE:
Test numbers refer to numbers on diagnostic chart.
- If temperature reading changes after disconnecting sensor, BCM and wiring are okay.
- If temperature reading changes after jumpering sensor terminals, BCM and wiring are okay.
- By applying ground to various points in circuits, an open can be isolated when temperature display changes from about -29°F to 194°F (-34°C to 90°C).