BCM Code F13: In-Car Temperature Sensor: Notes

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

The in-car temperature sensor uses a thermistor to control signal voltage to BCM. BCM applies and monitors voltage on circuit No. 734 to sensor. When sensor is cold, its resistance is high (BCM will read a high monitored voltage). As sensor warms, its resistance decreases and the signal voltage is pulled low through sensor ground (circuit No. 736). This signal will vary between 5 volts (open circuit) and zero volts (shorted circuit). Code F13 will set if signal voltage indicates less than -29°F (-34°C) or greater than 205°F (96°C). These conditions can be observed in BCM data display as an in-car temperature reading (parameter P.2.5) outside range.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) If temperature reading changes after disconnecting sensor, the BCM and wiring are okay.

Test Number 2) If temperature reading changes after jumpering sensor terminals, the BCM and wiring are okay.

Test Number 3) By applying a ground to various points in circuit, an open can be isolated when display changes from -29°F to 194°F (-34°C to 90°C).