DTC 123

DTC 123 Chart:

A/C Compressor Control Circuit:

CIRCUIT DESCRIPTION
The A/C low side temperature sensor is a thermistor that controls the signal voltage to the Powertrain Control Module (PCM). The PCM applies a voltage on CKT 731 to the sensor. When the sensor is cold, its resistance is high, therefore the PCM 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 808. This signal voltage will vary between 5V (open circuit) and OV (shorted circuit).

DTC 123 WILL SET WHEN
DTC 123 will set if the ignition is "ON," the outside temperature sensor has not failed and reads above 0°C (32°F), and the signal voltage indicates less than -38°C (open circuit) or over 53°C (shorted circuit). During the time the failure is present, a substitute temperature reading (the same value as outside air temperature) will be implemented to allow continued operation of the climate control system, also the compressor clutch will be disabled. The A/C low side temperature reading on the Tech 1 will, however, display the actual sensor reading.

DTC 123 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. PCM data value on the Tech 1 displays A/C low side temperature. The normal range is from -38°C to 53°C.
2. Check to see if the open circuit reading is due to the circuit or the sensor. If the open circuit reading changes to a shorted circuit reading after jumping the sensor terminals, the PCM and wiring are OK.
3. By applying a ground to various points in the circuits, an open can be isolated by observing whether the parameter display can be changed from the open reading to the shorted reading.
4. Check to see if the shorted circuit reading is due to the circuit or the sensor.

If the shorted circuit reading changes to an open circuit reading after disconnecting the sensor, the PCM and wiring are OK.

DIAGNOSTIC AIDS
If an intermittent DTC 123 is being set, manipulate the related wiring while observing PCM data on the Tech 1. If the failure is induced, the reading will jump from its normal value to a reading outside the range of -38°C to 53°C.
If the value of the sensor, displayed by Tech 1, is not reasonably close to the corresponding gage pressure reading, check for poor terminal contact or replace sensor.