*HVAC SYSTEM TEST
For a complete wiring diagramRefer to Section 8W.
Theory of Operation
The HVAC System Test provides a starting point in the diagnostic process byidentifying the appropriate diagnostic
procedure or system test to perform when diagnosing a given symptom, condition, or DTC. It also provides a means
for testing the entire HVAC system byutilizing the A/C-heater control’s On-Board System Tests. The On-Board Sys-
tem Tests can also assist in diagnosing stored DTCs. (Refer to 24 - HEATING &AIR CONDITIONING - DIAGNOSIS
AND TESTING) for additional information about on-board diagnostics.
Diagnostic Test
1.HVAC SYSTEM TEST
NOTE: Diagnose and repair all active DTCs before diagnosing and repairingstored DTCs.
Make a selection based on the symptom, condition, or DTC that you want to diagnose.
For Any Active DTC
Refer to the Table of Contents in this Section for a complete list of HVAC related symptoms.
Scan Tool Indicates HVAC Not Active On Bus
(Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - DIAGNOSIS AND TESTING) for no
response related diagnostic procedures.
Blower Motor Inoperative
Refer to *Blower Motor Inoperative in this Section.
Complete HVAC System Test
Go To 2
A/C System Performance Test
Go To 2
Mode Switch & Door Actuator Ckt Test
Go To 3
Actuator DTC Detection Test
Go To 4
Actuator Calibration Test
Go To 5
2.A/C SYSTEM PERFORMANCE TEST
NOTE: The following are prerequisites of the Cooldown Test. Verify each ofthe following before running the
test:
If active, diagnose and repair Evaporator Temperature Sensor related DTCs before proceeding. Refer to
the Table of Contents in this Section for a complete list of HVAC related symptoms.
Verify that the refrigerant system has an adequate charge. Check and repair as necessary before pro-
ceeding. (Refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - DIAGNOSIS ANDTESTING).
Verify that the blower motor operates correctly in all speeds. Diagnose and repair all blower related faults
before proceeding.
Verify that the work area ambient temperature is above 15.6°C (60°F) before proceeding. Move the vehicle
to a warmer work area if necessary.
Verify that the evaporator temperature is above 13°C (55°F) before proceeding.
Verify that the Mode Select control is set to the panel position.
Verify that the A/C compressor is not running. If the compressor is running, turn the A/C off and allow the
evaporator to warm up before proceeding.
NOTE: Running the AC Cooldown test will cause the A/C status indicator to flash.
NOTE: One or more status messages will display on the scan tool after running the Cooldown Test. These
messages will clear after paging back out of this test function. Therefore, it is important to note all mes-
sages before doing so.
Start the engine.
Turn the Blower control to the high speed position.
With the scan tool in HVAC, select System Tests and then select Cooldown test. Allow the test to run to completion.
Does the scan tool display a status message that indicates a fault has occurred?
Yes, Conditions Too Cold - Test Not Run
If running, turn the A/C compressor off. Verify that the work area ambient temperature is above 15.6°C
(60°F). If not, move the vehicle to a warmer work area. Verify that the evaporator temperature is above
13°C (55°F). If not, set the blower to high speed and allow the blower to run for five minutes. Then, run
the Cooldown Test again.
Yes, Blowers Not On High - Test Not Run
Set the blower speed to high speed and then run the Cooldown Test again.
Yes, No Results Stored/Test Not Complete
Verify that power is not interrupted while rerunning the Cooldown Test.
Yes, Refrigerant Temperature Sensor Error
For Dual-Zone HVAC systems, refer to B10B2–A/C COOL DOWN TEST PERFORMANCEfor the diag-
nostic test procedure. For Single-Zone HVAC systems, refer to B1079–CLIMATE CONTROL COOL
DOWN TEST EXCESSIVE TIME for the diagnostic test procedure.
Yes, DTC Set During Routine - Test Not Passed
For Dual-Zone HVAC systems, refer to B10B2–A/C COOL DOWN TEST PERFORMANCEfor the diag-
nostic test procedure. For Single-Zone HVAC systems, refer to B1079–CLIMATE CONTROL COOL
DOWN TEST EXCESSIVE TIME for the diagnostic test procedure.
No>>
Asnecessary,eitherGoTo3,4,or5,or Perform BODY VERIFICATION TEST - VER1. (Refer to 8 -
ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE).
3.MODE SWITCH & DOOR ACTUATOR CIRCUIT TEST
NOTE: If at anytime a DTC becomes active during this test, proceed to the conclusion question.
NOTE: If multiple DTCs are active, diagnose those that relate to a short circuit first.
NOTE: Dual-Zone A/C Heater Controls do not set DTCs for stuck mode switches. Therefore, verify that the
A/C Heater Control is not damaged and that the mode switches and status indicators function properly and
repair as necessary before proceeding.
If not done so previously, start the engine.
Turn the Blower control to the low speed position.
Set the Blend control (single-zone) or Driver Blend control (dual-zone) to the full cold position.
If equipped, set the Passenger Blend control to the full cold position.
Monitor the scan tool for active HVAC DTCs while performing the following test steps.
If equipped, press the A/C mode switch on, wait 30 seconds, and then press itoff.
On Dual-Zone systems, press the Recirc mode switch on, wait 30 seconds, andthen press it off.
If equipped, press the EBL mode switch on, wait 30 seconds, and then press itoff.
Move the Blend control (single-zone) or Driver Blend control (dual-zone)from full cold to full hot, wait 30 seconds,
and then move it back to full cold.
If equipped, move the Passenger Blend control from full cold to full hot, wait 30 seconds, and then moved it back
to full cold.
Turn the Mode select control to the defrost position, wait 30 seconds, and then turn it to the panel position (dual-
zone) or panel / recirc position (single-zone). Wait 30 seconds before proceeding.
Does the scan tool display any active DTCs?
Ye s>>
Diagnose and repair the DTC(s). Refer to the Table of Contents in this Section for a complete list of
HVAC related symptoms.
No>>
If you are here due to a stored DTC, it is possible that a technician may not have erased the DTC
following a repair. If possible, verify if the vehicle was recently in for this type of service. Otherwise,
either Go To 4 or 5, or visually inspect the related wiring harness for chafed, pierced, pinched, and
partially broken wires and the wiring harness connectors for broken, bent, pushed out, and corroded
terminals, and repair as necessary.
Perform BODY VERIFICATION TEST - VER 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL
MODULES - STANDARD PROCEDURE).
4.ACTUATOR DTC DETECTION TEST
NOTE: The Actuator DTC Detection Test clears all door actuator related DTCs when the test is actuated.
If not done so previously, start the engine.
With the scan tool, select System Tests and then select Actuator DTC Detection. When the test is complete, select
View DTCs.
Does the scan tool display any DTCs?
Yes, Dual-Zone
Diagnose and repair the DTC(s). If multiple DTCs are present, beginning with the passenger blend door,
diagnose and repair all short high DTCs and then all short low DTCs. Refer tothe Table of Contents in
this Section for a complete list of HVAC related symptoms.
Yes, Single-Zone
Diagnose and repair the DTC(s). If multiple DTCs are present, beginning with the common circuit, diag-
nose and repair all short high DTCs and then all short low DTCs. Refer to the Table of Contents in this
Section for a complete list of HVAC related symptoms.
No>>
If you are here due to a stored DTC, it is possible that a technician may not have erased the DTC
following a repair. If possible, verify if the vehicle was recently in for this type of service. Otherwise,
either Go To 5 or visually inspect the related wiring harness for chafed, pierced, pinched, and partially
broken wires and the wiring harness connectors for broken, bent, pushed out, and corroded terminals,
and repair as necessary.
Perform BODY VERIFICATION TEST - VER 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL
MODULES - STANDARD PROCEDURE).
5.ACTUATOR CALIBRATION TEST
NOTE: For vehicles equipped with EBL, running the HVAC Door Recalibrationwill cause the EBL status
indicator to flash.
NOTE: The Actuator Calibration Test clears all door actuator related DTCswhen the test is actuated.
If not done so previously, start the engine.
With the scan tool, select System Tests and then select Actuator Calibration Test. When the test is complete, select
View DTCs.
Does the scan tool display any DTCs?
Ye s>>
Diagnose and repair the DTC(s). Refer to the Table of Contents in this Section for a complete list of
HVAC related symptoms.
No>>
No problem found. However, if you are here due to a stored DTC, it is possiblethat a technician may
not have erased the DTC following a repair. If possible, verify if the vehicle was recently in for this type
of service. Otherwise, visually inspect the related wiring harness for chafed, pierced, pinched, and par-
tially broken wires and the wiring harness connectors for broken, bent, pushed out, and corroded ter-
minals, and repair as necessary.
Perform BODY VERIFICATION TEST - VER 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL
MODULES - STANDARD PROCEDURE).
DIAGNOSIS AND TESTING
HEATING-A/C SYSTEM DIAGNOSTICS
CAUTION: Do not exchange A/C Heater Controls from vehicle to vehicle. Software versions differ between
models and model years. Installing an A/C Heater Control with software that is incompatible for a given
vehicle can result in either improper or failed HVAC system operation.
ON-BOARD DIAGNOSTICS
The A/C-heater control communicates on the controller area network (CAN)B bus and is fully addressable with a
scan tool.
The A/C-heater control’s primary means of fault detection is through active and stored diagnostic trouble codes
(DTCs). 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 which occurred in the system since the A/C-heater control
received the last clear diagnostic info message. DTCs must be read with a scan tool. Refer to 24 - HVAC - Elec-
trical Diagnostics for HVAC DTC diagnostic test procedures.
The A/C-heater control’s secondary means of fault detection is through system tests. These tests include the HVAC
System Test, the A/C Cooldown Test, Actuator Calibration, and Actuator DTC Detection. Refer to System Tests in
this Section for a detailed description of each test.
SYSTEM TESTS
HVAC System Test
The HVAC System Test, found in 24 - HVAC - Electrical Diagnostics, providesa starting point in the diagnostic
process by identifying the appropriate diagnostic procedure or system test to perform when diagnosing a given
symptom, condition, or DTC. It also provides a means for testing the entireHVAC system by utilizing the A/C-heater
control’s On-Board System Tests. The On-Board System Tests can also assistindiagnosingstoredDTCs.
A/CCOOLDOWNTEST
The A/C Cooldown Test:
is actuated with a scan tool.
tests A/C system performance based on evaporator temperature sensor input.
will fail if evaporator temperature isbelow 13°C (55°F) when initiating the test.
will pass if the evaporator temperature drops 11°C (20°F).
indicates an outcome by displaying one or more test status messages on the scan tool. These test status
messages will clear after paging back out of this test function. Therefore, is it important to note all of the mes-
sages before doing so.
will cause the A/C status indicator to flash while the test is running.
ACTUATOR CALIBRATION FUNCTION
The Actuator Calibration function:
is actuated with a scan tool.
clears all actuator related DTCs when the test is actuated.
homes and repositions door actuators.
monitors for door span faults. Door span faults (XXX Door Travel Range Too Large or XXX Door Travel Range
Too Small) will only display after calibration.
will cause the electric backlight (EBL) status indicator (if equipped) toflash while the test is running.
ACTUATOR DTC DETECTION TEST — DUAL-ZONE
The Actuator DTC Detection Test:
is actuated with a scan tool.
clears all actuator related DTCs when the test is actuated.
supplements the continuous diagnostics on the actuator drive system.
monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simul-
taneous shorts. Shorted actuator circuit faults (XXX Control Circuit High or XXX Control Circuit Low) will only
display after running the Actuator DTC Detection Test.
After repairing each DTC, cycle the ignition switch, and then run the Actuator DTC Detection Test again to ensure
that no new DTCs exist. If multiple DTCs are present, beginning with the passenger blend door, diagnose and repair
all short high faults and then short low faults. When the test returns passed, clear all faults and run the Actuator
Calibration function as a final check of system health.
ACTUATOR DTC DETECTION TEST — SINGLE-ZONE
The Actuator DTC Detection Test:
is actuated with a scan tool.
clears all actuator related DTCs when the test is actuated.
supplements the continuous diagnostics on the actuator drive system.
monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simul-
taneous shorts. Shorted actuator circuit faults (XXX Control Circuit High or XXX Control Circuit Low) will only
display after running the Actuator DTC Detection Test.
After repairing each DTC, cycle the ignition switch, and then run the Actuator DTC Detection Test again to ensure
that no new DTCs exist. If multiple DTCs are present, beginning with the common circuit, diagnose and repair all
short high faults and then short low faults. When the test returns passed, clear all faults and run the Actuator Cal-
ibration function as a final check of system health.
A/C PERFORMANCE
The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. The
A/C evaporator, located in the HVAC housing is cooled to temperatures nearthe freezing point. As warm damp air
passes over the fins of the A/C evaporator, the air transfers its heat to therefrigerant in the evaporator coils and the
moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an A/C system will
be more effective in the Recirculation mode (max-A/C). With the system in the Recirculation mode, only air from the
passenger compartment passes through the A/C evaporator. As the passenger compartment air dehumidifies, the
A/C system performance levels rise.
Humidity has an important bearing on the temperature of the air delivered to the interior of the vehicle. It is impor-
tant to understand the effect that humidity has on the performance of the A/C system. When humidity is high, the
A/C evaporator has to perform a double duty. It must lower the air temperature, and it must lower the temperature
of the moisture in the air that condenses on the evaporator fins. Condensing the moisture in the air transfers heat
energy into the evaporator fins and coils. This reduces the amount of heat the A/C evaporator can absorb from the
air. High humidity greatly reduces the ability of the A/C evaporator to lower the temperature of the air.
However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing some of the
moisture out of the air entering the vehicle adds to the comfort of the passengers. Although, an owner may expect
too much from their A/C system on humid days. A performance test is the best way to determine whether the sys-
tem is performing up to design standards. This test also provides valuableclues as to the possible cause of trouble
with the A/C system. The ambient air temperature in the location where the vehicle will be tested must be a mini-
mum of 21° C (70° F) for this test.
A/C PERFORMANCE TEST
WARNING: Refer to the applicable warnings and cautions for this system before performing the following
operation (Refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNINGS) and (Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING - CAUTIONS). Failure to follow the warnings and cautions could result
in possible personal injury or death.
EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION
STATE DISPLAY TEST MODE ................. 2
CIRCUIT ACTUATION TEST MODE............ 2
DIAGNOSTIC TROUBLE CODES .............. 2
TASK MANAGER ............................. 2
MONITORED SYSTEMS ...................... 2
TRIP DEFINITION ............................ 5COMPONENT MONITORS .................... 6
OPERATION
OPERATION ................................. 6
TASK MANAGER ............................. 7
NON-MONITORED CIRCUITS................ 10
EVAPORATIVE EMISSIONS................12
EXHAUST GAS RECIRCULATION...........51
EMISSIONS CONTROL
DESCRIPTION
STATE DISPLAY TEST MODE
The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this
reason, the PCM cannot recognize the difference between a selected switchposition versus an open circuit, a short
circuit, or a defective switch. If the State Display screen shows the changefromHIGHtoLOWorLOWtoHIGH,
assume the entire switch circuit to the PCM functions properly. Connect the DRB scan tool to the data link con-
nector and access the state display screen. Then access either State Display Inputs and Outputs or State Display
Sensors.
CIRCUIT ACTUATION TEST MODE
The Circuit Actuation Test Mode checks for proper operation of output circuits or devices the Powertrain Control
Module (PCM) may not internally recognize. The PCM attempts to activate these outputs and allow an observer to
verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay
contacts, fuel spray, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the
device, its associated wiring, and driver circuit work correctly. Connect the DRB scan tool to the data link connector
and access the Actuators screen.
DIAGNOSTIC TROUBLE CODES
A Diagnostic Trouble Code (DTC) indicates the PCM has recognized an abnormal condition in the system.
Remember that DTC’s are the results of a system or circuit failure, but do not directly identify the failed
component or components.
BULB CHECK
Each time the ignition key is turned to the ON position, the malfunction indicator (check engine) lamp on the instru-
ment panel should illuminate for approximately 2 seconds then go out. Thisis done for a bulb check.
OBTAINING DTC’S USING DRB SCAN TOOL
1. Obtain the applicable Powertrain Diagnostic Manual.
2. Obtain the DRB Scan Tool.
3. Connect the DRB Scan Tool to the data link (diagnostic) connector. This connector is located in the passenger
compartment at the lower edge of instrument panel, and near the steering column.
4. Turn the ignition switch on and access the “Read Fault” screen.
5. Record all the DTC’s and “freeze frame” information shown on the DRB scantool.
6. To erase DTC’s, use the “Erase Trouble Code” data screen on the DRB scan tool.Do not erase any DTC’s
until problems have been investigated and repairs have been performed.
TA S K M A N A G E R
The PCM is responsible for efficiently coordinating the operation of all the emissions-related components. The PCM
is also responsible for determining if the diagnostic systems are operating properly. The software designed to carry
out these responsibilities is called the ’Task Manager’.
MONITORED SYSTEMS
There are new electronic circuit monitors that check fuel, emission, engine and ignition performance. These moni-
tors use information from various sensor circuits to indicate the overalloperation of the fuel, engine, ignition and
emission systems and thus the emissions performance of the vehicle.
The fuel, engine, ignition and emission systems monitors do not indicate aspecific component problem. They do
indicate that there is an implied problem within one of the systems and thata specific problem must be diagnosed.
If any of these monitors detect a problem affecting vehicle emissions, theMalfunction Indicator Lamp (MIL) will be
illuminated. These monitors generate Diagnostic Trouble Codes that can be displayed with the MIL or a scan tool.
COMPONENT MONITORS
There are several components that will affect vehicle emissions if they malfunction. If one of these components
malfunctions the Malfunction Indicator Lamp (MIL) will illuminate.
Some of the component monitors are checking for proper operation of the part. Electrically operated components
now have input (rationality) and output (functionality) checks. Previously, a component like the Throttle Position sen-
sor (TPS) was checked by the PCM for an open or shorted circuit. If one of these conditions occurred, a DTC was
set. Now there is a check to ensure that the component is working. This is donebywatchingforaTPSindication
of a greater or lesser throttle opening than MAP and engine rpm indicate. Inthe case of the TPS, if engine vacuum
is high and engine rpm is 1600 or greater, and the TPS indicates a large throttle opening, a DTC will be set. The
same applies to low vacuum if the TPS indicates a small throttle opening.
All open/short circuit checks, or any component that has an associated limp-in, will set a fault after 1 trip with the
malfunction present. Components without an associated limp-in will taketwo trips to illuminate the MIL.
OPERATION
OPERATION
The Powertrain Control Module (PCM) monitors many
different circuits in the fuel injection, ignition, emission
and engine systems. If the PCM senses a problem
withamonitoredcircuitoftenenoughtoindicatean
actual problem, it stores a Diagnostic Trouble Code
(DTC) in the PCM’s memory. If the problem is repaired
or ceases to exist, the PCM cancels the code after 40
warm-up cycles. Diagnostic trouble codes that affect
vehicle emissions illuminatethe Malfunction Indicator
Lamp (MIL). The MIL is displayed as an engine icon
(graphic) on the instrument panel. Refer to Malfunction
Indicator Lamp in this section.
Certain criteria must be met before the PCM stores a
DTC in memory. The criteria may be a specific range
of engine RPM, engine temperature, and/or input volt-
age to the PCM.
The PCM might not store a DTC for a monitored cir-
cuit even though a malfunction has occurred. This
may happen because one of the DTC criteria for the
circuit has not been met.For example,assume the diagnostic trouble code criteria requires the PCM to monitor the
circuit only when the engine operates between 750 and 2000 RPM. Suppose thesensor’s output circuit shorts to
ground when engine operates above 2400 RPM (resulting in 0 volt input to thePCM). Because the condition hap-
pens at an engine speed above the maximum threshold (2000 rpm), the PCM willnot store a DTC.
There are several operating conditions for which the PCM monitors and setsDTC’s. Refer to Monitored Systems,
Components, and Non-Monitored Circuits in this section.
Technicians must retrieve stored DTC’s by connecting the DRB scan tool (oran equivalent scan tool) to the 16–way
data link connector. The connector is located on the bottom edge of the instrument panel near the steering column.
NOTE: Various diagnostic procedures may actually cause a diagnostic monitor to set a DTC. For instance,
pulling a spark plug wire to perform a spark test may set the misfire code. When a repair is completed and
verified, connect the DRB scan tool to the 16–way data link connector (1) toerase all DTC’s and extinguish
the MIL.