Code F13 - In-Car Temperature Sensor: Notes

Fig 1: BCM Code F13 Schematic - In-Car Temperature Sensor

The in-car temperature sensor uses a thermistor to control signal voltage to BCM. The 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.

1. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, the BCM and wiring are okay.
2. If open circuit reading changes to a shorted circuit reading after jumpering sensor terminals, the BCM and wiring are okay.
3. By applying a ground to various points in circuit, an open can be isolated by observing whether parameter display can be changed from open reading to a shorted reading.