System Diagnostics

Fault detection is through active and stored Diagnostic Trouble Codes (DTCs)

DTCs are displayed by the DRBIII®.
Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired in order to clear this type of DTC.
Stored DTCs are those that occurred in the system since the ATC received the last "clear diagnostic info" message.

The AC Cooldown Test:

is actuated with the DRBIII®.
checks A/C system performance based on evaporator temperature sensor input.
will not run:
- if ambient temperature is below 12°C (53°F).
- if A/C pressure is below 50 psi or above 300 psi
- if the evaporator temperature sensor/circuit is open.
- if the evaporator temperature sensor/circuit is shorted.
will pass if the evaporator temperature drops either 6.7°C (20°F) within two minutes at ambient temperatures of 21°C (70°F) or above, or if the evaporator temperature drops 9.4°C (15°F) within two minutes at ambient temperatures below 21°C (70°F).
messages display on the DRBIII® after running this test.
- These messages will clear after paging back out of this test. Therefore, it is important to note all of the AC Cooldown test messages before doing so.
will cause the DELAY VF segment and Snowflake LED on the ATC to flash. If the test fails the VF segment and LED will continue to flash until either the vehicle is driven more than three miles or a successful AC Cooldown Test is performed.

Actuator Calibration:

occurs after turning on the ignition after a battery reconnect.
occurs after ATC installation or replacement.
occurs after 20 ignition cycles.
can be initiated by the DRBIII® by selecting Body, Automatic Temperature Control, Miscellaneous, and Reset ATC Head.
can be initiated by pressing the PWR and RECIRC buttons simultaneously for five seconds.
- Manual motor calibration will cause the DELAY and RECIRC VF segments on the ATC to flash. If the test fails the VF segments will continue to flash until either the vehicle is driven more than three miles or a successful calibration occurs.

Ambient Temperature Sensor Faults:

NOTE: The Outside Air Temperature (OAT) display can be activated and de-activated by pressing the Outside Temp button on the ATC.

NOTE: Anytime the vehicle is turned off for more than 2 hours, the OAT display will update instantly upon ignition on. However, if the vehicle is turned off for less than 2 hours and the outside air temperature increases, the OAT display may display a value that is colder than the actual outside air temperature. This is due to filtering which does not allow for instantaneous updates for warmer outside air temperatures. Also, if the vehicle is driven for an extended period of time below 20 mph the OAT display will not update for warmer outside air temperatures. If after the extended period of time driving below 20 mph the vehicle speed is increased to above 50 mph the OAT display may display an erroneous "too warm" value. This is due to extended idle speeds that create hot sensors due to engine heat.

The OAT function is supported by the Ambient Temperature Sensor (ATS), a signal circuit and a ground circuit which is hardwired to the NGC and OAT data that is bussed from the NGC to the ATC where the outside air temperature is displayed. If the ATS sense circuit is shorted to ground, the OAT display will display 130°F (54°C). If the ATS sense circuit is open, the OAT display will display -40°F (-40°C). When diagnosing OAT display related symptoms, always check the ATS and related circuits before testing the ATC. Ambient Temperature Sensor Diagnostic Trouble Codes (DTCs) are stored in the NGC. The ATS can be checked using the following Ambient Temperature Sensor Test.

Ambient Temperature Sensor Test

Turn the ignition OFF.
Disconnect the ATS harness connector.
Measure the resistance of the ATS using the following min/max values:
- 32°F (0°C) Sensor Resistance = 29.33 - 35.99 Kilohms
- 50°F (10°C) Sensor Resistance = 17.99 - 21.81Kilohms
- 68°F (20°C) Sensor Resistance = 11.37 - 13.61Kilohms
- 77°F (25°C) Sensor Resistance = 9.12 - 10.86 Kilohms
- 86°F (30°C) Sensor Resistance = 7.37 - 8.75 Kilohms
- 104°F (40°C) Sensor Resistance = 4.90 - 5.75 Kilohms

The sensor resistance should read between these min/max values. If the resistance values are not OK, replace the Sensor.