DTC 120

DTC 120 Chart:

A/C Compressor Control Circuit:

*** Test Revised per TSB 51-65-04 ***

CIRCUIT DESCRIPTION
The A/C low side temperature sensor uses a thermistor to control 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 the signal voltage is pulled low through the sensor ground, CKT 808. DTC 120 will set if the signal voltage indicates less than -37°C (-35°F) (open Circuit) or over 99°C (210°F) (shorted Circuit) with the outside air temperature between the range specified. These conditions can be observed in the Tech 1 data display as an "A/C Low Side Temp" reading.

DTC 120 WILL SET WHEN
- Outside air temperature sensor failure not indicated by the HVAC controller.
- Outside air temperature between 4°C (40°F) and 99°C (210°F).
- A/C low side temperature sensor less than -37°C (-35°F) or greater than 99°C (210°F).

ACTION TAKEN (PCM WILL DEFAULT TO)
- Disable A/C compressor clutch.
- DTC 120 does not illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).

DTC 120 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. Determines if conditions to set DTC 120 are present.
2. If Tech 1 displays "A/C Low Side Temp" greater than 99°C (210°F) with A/C low temperature sensor disconnected and terminals "A" and "B" jumpered together CKTs 731 and 808 are OK.
3. If Tech 1 displays "A/C Low Side Temp" less than -37°C (-35°F) with A/C low temperature sensor disconnected the A/C low side temperature sensor is faulty.
4. When CKT 731 is jumpered to ground, the Tech 1 should display "A/C Low Side Temp" greater than 99°C (210°F).
5. When backprobing PCM terminal "C10" to ground the Tech 1 should display "A/C Low Side Temp" greater than 99°C (210°F).