F12

BCM Code F12:

Outside Air Temperature Circuit:

DESCRIPTION:

If this code is NOT displayed during the second pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The A/C low side temperature sensor uses a thermistor to control the signal voltage to the BCM. The BCM applies a voltage on CKT 731 to the sensor. When the sensor is cold its resistance is high, therefore the BCM will see a high signal voltage. As the sensor warms, its resistance becomes less and the signal voltage is pulled low through the sensor ground, CKT 736. This signal voltage will vary between 5 and 0 volts .

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
Code F12 will set if the signal voltage indicates less than -34°C (open circuit) or over 87°C (grounded circuit). These conditions can be observed in BCM data display as an "A/C low side temp" reading (parameter P.2.8) outside the range of -34°C to 87°C.

1. If the temp reading changes after disconnecting the sensor, the BCM and wiring are OK.

2. If the temp reading changes after jumpering the sensor terminals, the BCM and wiring are OK.

3. By applying a ground to various points in the circuit, the open may be isolated when the temp. display changes from about -34°C to about 90°C.

NOTE ON INTERMITTENTS:

If an intermittent code F12 is being set, manipulate the related wiring while observing BCM data parameter P.2.8. If the failure is induced, the reading will jump from its normal value to a reading outside the range of -34°C to 87°C. If the value displayed by P.2.8 is not reasonably close to a corresponding gauge pressure reading, check for poor terminal contact or replace sensor.