POSSIBLE CAUSES
CHECK FOR ACTIVE HVAC DTCS, & COOLDOWN TEST & DOOR RECALIBRATION MESSAGES
STORED CODE(S) TEST COMPLETE
TEST ACTION APPLICABILITY
1NOTE: Active codes must be resolved before diagnosing stored codes.
NOTE: Anytime a code becomes active during this test, proceed to the
conclusion question.
Turn the ignition on.
With the DRBIIIt, record and erase stored HVAC DTC's.
Cycle the ignition switch.
Start the engine.
Monitor the DRBIIItfor active HVAC DTCs while performing the following test
steps.
Manually press the A/C - Heater Control power switch on.
Turn the front blower motor control switch knob to the low position.
If equipped, turn the rear blower motor control switch knob to the low position.
Set the passenger blend control switch to the full cold position.
If equipped, set the zone/driver blend control switch to the full cold position.
Turn the mode select switch knob to the panel position.
Manually press the recirculation mode switch on, wait 30 seconds then press it off.
Manually press the A/C mode switch on, wait 30 seconds then press it off.
Manually press the rear window defogger switch on, wait 30 seconds then press it off.
Manually sweep the passenger blend control switch from full cold to full hot then
back to full cold.
If equipped, manually sweep the zone/driver blend control switch from full cold to full
hot then back to full cold.
Manually sweep the front blower motor control switch knob through all positions.
If equipped, manually sweep the rear blower motor control switch knob through all
positions.
If equipped, turn the rear blower motor control switch knob to the rear position.
If equipped, on the Rear Blower Rear Control, manually sweep the rear blower motor
control switch knob through all positions.
If equipped, on the Rear Blower Rear Control, manually sweep the rear blend/mode
control switch knob from full cold to full hot then back to full cold.
With the DRBIIIt, actuate the AC Cooldown Test.
With the DRBIIIt, actuate the HVAC Door Recalibration Test.
Place the vehicle on a hoist, and raise the wheels off the floor.
WARNING: Be sure to keep hands and feet clear of rotating wheels. Keep
clear of the engine's moving parts
Start the engine. Place the transmission in drive. Brake off.
Does the DRBIIItdisplay any active HVAC DTC(s), Cooldown Test or Door Recali-
bration message(s)?All
Ye s®Return to the symptom list and choose the symptom(s).
Perform BODY VERIFICATION TEST - VER 1.
No®No problem found at this time.
Perform BODY VERIFICATION TEST - VER 1.
518
HEATING & A/C
A/C FAULT (STORED) - MANUAL A/C ÐContinued
Symptom List:
BACKLIGHT DIMMING RX FAILURE (ACTIVE) - MANUAL A/C
NO BCM MESSAGE RECEIVED (ACTIVE) - MANUAL A/C
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be BACKLIGHT DIMMING RX
FAILURE (ACTIVE) - MANUAL A/C.
When Monitored and Set Condition:
BACKLIGHT DIMMING RX FAILURE (ACTIVE) - MANUAL A/C
When Monitored: With the ignition on.
Set Condition: If the A/C - Heater Control Module does not receive the dimming function
message from the BCM for more than 5 seconds, then the A/C - Heater Control Module
LEDs will default to full brightness and the DTC will set.
NO BCM MESSAGE RECEIVED (ACTIVE) - MANUAL A/C
When Monitored: With the igntion on.
Set Condition: If the A/C - Heater Control Module does not receive the dimming function
message from the BCM for more than 5 seconds, then the A/C - Heater Control Module
LEDs will default to full brightness and the DTC will set.
POSSIBLE CAUSES
ADDITIONAL CODE(S) PRESENT
A/C - HEATER CONTROL MODULE
BODY CONTROL MODULE - NO DIM MESSAGE TO A/C - HEATER CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, read the BCM codes.
Does DRBIIItdisplay Headlamp Switch: Mismatch; STG; Open; or Panel Dim
Output Short?All
Ye s®Refer to symptoms Headlamp Switch Mismatch, Headlamp
Switch Shorted To Ground, and Headlamp Switch Open in the
Exterior Lighting catagory. Refer to symptom Panel Dimming
Output Short in the Instrument Cluster catagory.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
519
HEATING & A/C
TEST ACTION APPLICABILITY
2 Turn the ignition on.
With the DRBIIItin Monitor Display, PCI Bus Messages, look for the VF DIM Msg
Present.
Does the DRB display: VF DIM Msg present: Yes?All
Ye s®Replace the A/C - Heater Control Module in accordance with the
Service Information.
Perform BODY VERIFICATION TEST - VER 1.
No®Replace the Body Control Module in accordance with the Service
Information.
Perform BODY VERIFICATION TEST - VER 1.
520
HEATING & A/C
BACKLIGHT DIMMING RX FAILURE (ACTIVE) - MANUAL A/C ÐContinued
ZONE CALIBRATION FAULT - MANUAL A/C
When Monitored: When the HVAC Door Recalibration is executed. With the ignition on
(door actuator(s)/circuit(s) shorted low only).
Set Condition: If the Blend Door (Driver [Zone]) drive span found is outside the tolerance.
If the Blend Door Actuator (Driver [Zone])/circuit is open. If the Blend Door(s) (Driver
[Zone], Pass, Rear), Mode Door(s) (Front, Rear), Recirculation Door Actuator(s)/circuit(s)
are shorted low. (This will also set Blend Calibration/Overcurrent (Front, Rear), Mode
Calibration/Overcurrent (Front, Rear), Recirculation Calibration/Overcurrent, Zone
Calibration/Overcurrent DTCs.)
POSSIBLE CAUSES
HVAC DTC(S) PRESENT
DOOR ACTUATOR
BLEND ACTUATOR/LINKAGE/DOOR
RECIRCULATION ACTUATOR/LINKAGE/DOOR
MODE ACTUATOR/LINKAGE/DOOR
DOOR ACTUATOR DRIVER CIRCUIT OPEN
COMMON DOOR DRIVER CIRCUIT OPEN
A/C - HEATER CONTROL MODULE
TEST ACTION APPLICABILITY
1NOTE: All Overcurrent DTCs must be repaired before diagnosing Calibra-
tion messages.
Turn the ignition on.
With the DRBIIIt, read HVAC DTCs.
Does the DRBIIItdisplay any HVAC DTCs?All
Ye s®Return to the symptom list and choose the symptom(s).
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
522
HEATING & A/C
BLEND CALIBRATION FAULT - MANUAL A/C ÐContinued
Symptom List:
COOLDOWN TEST EXCESSIVE FAULT - MANUAL A/C
COOLDOWN TEST SENSOR FAILURE - MANUAL A/C
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be COOLDOWN TEST EXCESSIVE
FAULT - MANUAL A/C.
When Monitored and Set Condition:
COOLDOWN TEST EXCESSIVE FAULT - MANUAL A/C
When Monitored: When executing the Cooldown Test.
Set Condition: This message will be displayed if the A/C system is unable to bring the
evaporator temperature down -6.7ÉC (20ÉF) within two minutes.
COOLDOWN TEST SENSOR FAILURE - MANUAL A/C
When Monitored: When executing the Cooldown Test.
Set Condition: This message will be displayed if a fault is detected with the Evaporator
Temperature Sensor/circuit when executing the Cooldown Test.
POSSIBLE CAUSES
HVAC DTC(S) PRESENT
CHECK THE PCM/ECM FOR DTCS
A/C SYSTEM TESTING
TEST ACTION APPLICABILITY
1CAUTION: The evaporator temperature must be above 12.7ÉC (55ÉF) to test
A/C system operation.
Turn the ignition on.
With the DRBIIIt, read HVAC DTCs.
Does the DRBIIItdisplay any HVAC DTCs?All
Ye s®Return to the symptom list and choose the symptoms(s).
After repair is complete, rerun the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
532
HEATING & A/C
Symptom:
COOLDOWN TEST SET UP FAULT - MANUAL A/C
When Monitored and Set Condition:
COOLDOWN TEST SET UP FAULT - MANUAL A/C
When Monitored: When executing the Cooldown Test.
Set Condition: This message will be displayed if the front blower is not operating at high
speed when executing the Cooldown Test.
POSSIBLE CAUSES
HVAC DTC(S) PRESENT
TEST SET UP CONDITIONS NOT MET
FRONT BLOWER/RELATED CIRCUITS
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, read HVAC DTCs.
Does the DRBIIItdisplay any HVAC DTCs?All
Ye s®Return to the symptom list and choose the symptoms(s). After the
repair is complete, with the DRBIIIt, erase the DTC(s). Cycle the
ignition switch. With the DRBIIIt, actuate the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 2
2 Was the Front Blower Front Control switch set to high speed when the Cooldown Test
was actuated?All
Ye s®Check the front blower motor and related circuits for front blower
operation problems. Repair as necessary. After repair is complete,
with the DRBIIIt, actuate the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Start the engine. Set the Front Blower Front Control switch to
high speed. With the DRBIIIt, actuate the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
534
HEATING & A/C
Symptom:
COOLDOWN TEST TOO COLD TO START - MANUAL A/C
When Monitored and Set Condition:
COOLDOWN TEST TOO COLD TO START - MANUAL A/C
When Monitored: When executing the Cooldown Test.
Set Condition: This message will be displayed if the A/C - Heater Control Module sees
evaporator temperature below 12.7ÉC (55ÉF) when executing the Cooldown Test.
POSSIBLE CAUSES
EVAPORATOR TEMPERATURE TOO LOW
HVAC DTC(S) PRESENT
CHECK THE PCM/ECM FOR DTCS
EVAPORATOR TEMPERATURE SENSOR
SENSOR GROUND CIRCUIT HIGH RESISTANCE
EVAPORATOR TEMPERATURE SENSOR SIGNAL CIRCUIT HIGH RESISTANCE
A/C - HEATER CONTROL MODULE
TEST ACTION APPLICABILITY
1CAUTION: The work area ambient temperature must be above 15.6ÉC (60ÉF)
to test A/C system operation.
Start the engine.
Turn the A/C off.
Turn the Blower on high. Allow the blower to run for 5 minutes to ensure that the
Evaporator Temperature Sensor temperature is above 12.7ÉC (55ÉF).
With the DRBIIIt, actuate the Cooldown Test.
Does the DRBIIItdisplay: Cooldown Test Too Cold To Start?All
Ye s®Go To 2
No®Perform additional testing as necessary.
Perform BODY VERIFICATION TEST - VER 1.
2CAUTION: The work area ambient temperature must be above 15.6ÉC (60ÉF)
to test A/C system operation.
Turn the ignition on.
With the DRBIIIt, read HVAC DTCs.
Does the DRBIIItdisplay any HVAC DTCs?All
Ye s®Return to the symptom list and choose the symptom(s). After the
repair is complete, with the DRBIIIt, erase the DTC(s). Cycle the
ignition switch. With the DRBIIIt, actuate the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 3
535
HEATING & A/C
TEST ACTION APPLICABILITY
3CAUTION: The work area ambient temperature must be above 15.6ÉC (60ÉF)
to test A/C system operation.
Turn the ignition on.
With the DRBIIIt, check the PCM/ECM for DTCs.
Are any DTCs present?All
Ye s®Refer to Powertrain Diagnostic information for the related symp-
tom(s). After the repair is complete, with the DRBIIIt, erase the
DTC(s). Cycle the ignition switch. With the DRBIIIt, actuate the
Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 4
4 Turn the ignition off.
Disconnect the Evaporator Temperature Sensor harness connector.
Turn the ignition on.
With the DRBIIItin Sensor Display, read the Evaporator Temperature Sensor
voltage.
Is the voltage above 4.9 volts?All
Ye s®Go To 5
No®Go To 6
5 Turn the ignition off.
Disconnect the Evaporator Temperature Sensor harness connector.
Connect a jumper wire between the Evaporator Temperature Sensor Signal circuit
and the Sensor Ground circuit at the Evaporator Temperature Sensor harness
connector.
Turn the ignition on.
With the DRBIIItin Sensor Display, read the Evaporator Temperature Sensor
voltage.
Is the voltage 0.0 volts?All
Ye s®Replace the Evaporator Temperature Sensor in accordance with
the Service Information. After repair is complete, rerun the
Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
No®Go To 6
6NOTE: Ensure that the voltmeter leads meet the terminals in the connector
and that there is good terminal to wire connection.
NOTE: Ensure the voltmeter leads are connected for positive polarity.
Back probe the Sensor Ground circuit between the Evaporator Temperature Sensor
harness connector and the A/C - Heater Control Module C1 harness connector.
Turn the ignition on.
Is the voltage below 0.10 volt?All
Ye s®Go To 7
No®Repair the high resistance in the Sensor Ground circuit. After
repair is complete, rerun the Cooldown Test.
Perform BODY VERIFICATION TEST - VER 1.
536
HEATING & A/C
COOLDOWN TEST TOO COLD TO START - MANUAL A/C ÐContinued