Part 3B

Horn relay
The horn relay operates through a direct wire input to the FCM from the horn switch (FCM pin 17) , or a PCI Bus message from the BCM. The relay responds to the horn switch, remote door lock and VTA alarm functions. The horn relay is powered through low side control on pin 10 of the FCM. Under normal operating conditions, if the horn is pressed for longer than 30 seconds, the FCM will automatically deactivate the horn to prevent damage to it. The FCM will re-activate control of the relay after a 25 second cool-down period. This circuit is electronically controlled and continuously monitored for malfunctions.

Front and rear blower relay
The blower control switch is part of the Automatic Temperature Control (ATC) or A/C-Heater Control Module, (Manual Temp). When the blower switch is turned ON, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The front and rear blower relay is then powered through low side control on pin 30 of the FCM. The relay provides the high side to the blower motor, and the blower speed is governed through low side control in the ATC or A/C-Heater Control Module. This circuit is electronically controlled and continuously monitored for malfunctions.

Name Brand Speakers (NBS) relay
The NBS relay operates through the vehicle bus interface between the radio and the FCM. When the radio is turned on, the radio sends a PCI Bus message to the FCM. The NBS relay is then powered on through low side control on pin 11 of the FCM. The relay supplies power to the amplified speaker, and ground is supplied through the radio. This circuit is electronically controlled and continuously monitored for malfunctions.

Electronic Back Light (EBL) relay
The rear defrost switch is part of the Automatic Temperature Control or A/C-Heater Control Module (Manual Temp). When the ignition switch is in the RUN position and the rear defrost switch is turned ON, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The EBL run only relay is then powered through low side control on pin 31 of the FCM. The relay provides the high side to the rear window defrost grid, and ground is attached to the vehicle body. The FCM will only allow the rear defrost to operate in the RUN position. This circuit is electronically controlled and continuously monitored for malfunctions.

Electrical Inputs
Headlamp battery supplies 1 & 2 - 12 volt input on pins 1 and 2. Battery supply voltage for switching headlamp circuits only.

Module battery supply - 12 volt input on pin 9. Battery supply voltage for all other FCM operations.

Power ground - Ground source on pin 8 for all FCM operations.

Ignition switch RUN or START position status - 12 volt input on pin 37. Allows the FCM to determine the ignition switch status for related FCM operations.

Ignition switch START only status - 12 volt input on pin 19. Allows the FCM to discriminate between RUN/START input and START for related FCM operations.

PCI Bus - Approximately 7.5 volt input on pin 22. Allows the FCM to communicate with other modules on the vehicle bus.

Stop lamp Switch status - 12 volt input on pin 44. Provides for brake shift interlock function.

Horn Switch - Ground input on pin 17. Primary means for engaging the horn.

Back-up switch - Ground input on pin 39. Input is converted to a PCI Bus status message for use by other modules.

Wiper park switch - Ground input on pin 16. Used to determine park placement of wipers. Also used as feedback to FCM to determine correct operating mode of wipers.

Washer fluid level switch - Ground input to pull-up on pin 18. Ground is switched into the circuit when washer bottle fluid level is low.

Brake fluid level switch - Ground input to pull-up on pin 36. Ground is switched into the circuit when brake fluid level is low.

Ambient temperature sensor - Resistive input to pull-up on pin 25. Corresponding voltage level is converted to a PCI Bus message for use by other modules on the bus.

Right park lamp outage - 12 volt input on pin 21. Used to determine if right park lamp circuit is operating properly.

Left park lamp outage - 12 volt input on pin 41. Used to determine if left park lamp circuit is operating properly.

Battery IOD - 12 volt input on pin 20. The FCM enters a low power consumption mode when the ignition is turned OFF. This low current draw battery supply keeps the microprocessor functioning in the low power mode.

Battery (+) connection detection - 12 volt input on pin 38. The battery connection on the PDC incorporates the use of an internal switch to deter- mine if the connector is properly mated and the Connector Positive Assurance (CPA) is engaged. If the CPA is not properly engaged, a voltage on pin 38 will be interpreted as an unseated connector and a fault will set.

Flash programming voltage - 20 volt input on pin 42. When a DRBIII(R) is connected and the proper flash reprogramming sequence is selected, the 20 volt signal will be applied through pin 42.

HEATING & A/C
Automatic Temperature Control (ATC)
System Operation
The Automatic Temperature Control (ATC) system provides fully adjustable three zone climate control; Driver front zone, Passenger Front zone and Rear zone. The following is a list of ATC controls and features:
- a POWER button which allows the operator to turn the system completely OFF.
- AUTO HIGH/LOW switch allows the operator to select what rate (fan speed) the system will provide the selected comfort level.
- DRIVER, REAR and PASSENGER rocker switches to select desired temperature for each zone.
- Recirculation button allows cooling air to be recirculated which maximizes cooling ability.
- A/C select button allows the operator to turn the A/C compressor off.
- Defroster button allows the operator to turn on the defroster independently during automatic control.
- Fan control rotary switch for selecting fan speed.
- Mode rotary switch for selecting heating/ cooling direction.
- REAR SYSTEM rotary switch for activating the Rear ATC Switch allowing intermediate passenger control over rear climate control.

Blower Motor Operation
The Automatic Temperature Control (ATC) front and rear blower control provides continuously variable control of air flow rate to meet occupant comfort requirements. Pulse width modulation of the blower motor power allows the front and rear blower to operate at any speed from off to full speed. When front or rear blower operation is required, the ATC sends a PCI Bus message to the Front Control Module (FCM) requesting blower relay ON. The FCM provides a ground for the front and rear blower motor relay coils, activating both relays. The front and rear blower relays provide 12 volts to their respective blower motor power modules. Each module provides a 12 volt blower motor control signal to the ATC. The ATC provides a pulse width modulated (duty-cycle) ground signal to this circuit based on climate requirements. The higher voltage on the signal circuit (less duty-cycle ground) the lower the blower speed request. The lower voltage on the signal circuit (more duty-cycle ground) the higher the blower speed request.

Infrared Sensors
The ATC system uses infrared (I/R) sensors to monitor and control occupant comfort levels. This sensing system replaces interior air temperature and solar sensors which required complex control programs to maintain occupant comfort levels. The front I/R sensor is located in the instrument panel center bezel outlet. The rear I/R sensor is located in the rear overhead mounted ATC switch.

Rear ATC Switch
The rear ATC switch is mounted in the headliner. The switch contains a rotary adjustment for fan speed, a rotary adjustment for mode selection, a push button switch for temperature selection and a digital display of the selected temperature.

Cooldown Testing
The ATC provides a feature referred to as a Cooldown Test. This test is initiated using the DRBIII(R) and is designed to check the performance of the air conditioning system. The ATC will not perform this test if the ambient air temperature is below 12 °C (53 °F). During the test, the ATC compares the ambient air temperature to the evaporator temperature sensor. To pass the cooldown test, the evap temperature sensor must drop -6 °C (20 °F) below ambient temperature within 2 minutes of start of test. At the completion of the cooldown test the DRBIII(R) will display one of the following messages indicating test outcome:
- Cooldown Test Passed
- Cooldown Test Failed
- Evap Temp Sensor Shorted
- Evap Temp Sensor Open
- A/C Pressure Too Low
- A/C Pressure Too High
- Invalid Conditions for Cooldown Test, Evap Temperature Too Low

If a message other than Cooldown Test Passed occurs, refer to the appropriate symptom for diagnosis.

Active And Stored Trouble Codes
The Automatic Temperature Control (ATC) is capable of storing Active and Stored trouble codes. Active codes indicate a current fault in the system. Stored codes indicate that a problem has occurred in the system, however is not currently present. Active codes cannot be erased until the problem causing the code has been repaired. At this time the Active code is converted to a Stored code, which can be erased using the DRBIII(R).

Manual Temperature Control
System Availability
Depending on the model, up to three different HVAC systems are currently available in these vehicles. A Single-Zone Air Conditioning System, a Dual-Zone Air Conditioning System, and a Three-Zone Air Conditioning System.

Zone Control
The Single-Zone Air Conditioning System maintains incoming air temperature, airflow, fan speed, and fresh air intake for the entire vehicle from the instrument panel mounted A/C - Heater Control Module. The full range of temperature that the system can produce in any mode for the entire vehicle is available by positioning the blend control to the desired range.

The Dual- and Three-Zone Air Conditioning systems allow completely independent side-to-side control of incoming air temperature. The full range of temperature that the front system can produce in any mode is available on either side of the vehicle by positioning the independent driver and passenger blend controls to the desired range. The three- zone system also allows the front seat occupants to completely control the Rear A/C - Heater Unit from the instrument panel mounted A/C - Heater Control Module. The intermediate and rear seat occupants can also regulate the air temperature and the fan speed of the rear unit from the rotary controls on the headliner mounted Rear Blower Rear Control.

Front HVAC Unit
The front compartment HVAC unit has five fully adjustable instrument panel outlets. Side-window demister outlets in the instrument panel eliminate door ducts and door-to-instrument panel seals. A single, central mounted outlet delivers air for defrosting the windshield. Air exhausters allow air entering at the front of the vehicle to flow out the back to the rear occupants. Models equipped with Dual-Zone and Three-Zone A/C systems include a dust and odor air filter.

Mid-cabin comfort control directs only cooling airflow to the intermediate seat occupants through outlets at the rear of each front door trim panel. Air is supplied to these outlets from the instrument panel through ducts in the doors that use molded seals at the instrument panel to prevent air leakage. Wide outlets under the front seats with directional dividers distribute heated air across the floor to the intermediate seat occupants. Ducts in the center of the vehicle under the carpet deliver air from the front compartment HVAC unit to these outlets.

Overhead outlets along the roof rails adjacent to each rear seat and three outlets in the right quarter panel near the floor distribute air to the intermediate and rear seat occupants.

Rear HVAC Unit
The rear A/C - heating unit provides air temperature modulation by utilizing a temperature door to allow variable proportions of cooled and heated air to mix to achieve a desired ambient temperature. Also, a variable mode control in the rear unit allows proportioned airflow between the floor and overhead outlets.

A/C - Heater Control Module, Switch Operation
Power Switch
The Power Switch is a momentary contact switch. The switch LED illuminates when the switch is ON. The Power Switch setting is remembered during power down.

Rear Window Defogger Switch
The Rear Window Defogger Switch is a momentary contact switch. Toggling the switch results in the A/C - Heater Control Module sending a change of state message to the FCM to provide rear window defogger activation or deactivation respectively. The switch LED illuminates when the switch is ON.

Recirculation Switch
The Recirculation Switch is a momentary contact switch. Toggling the switch ON results in the A/C - Heater Control Module signaling the actuator to close the fresh-air door. Toggling the switch OFF results in the A/C - Heater Control Module signaling the actuator to open the fresh-air door. The switch LED illuminates when the switch is ON. When the Power Switch is OFF, the A/C - Heater Control Module closes the fresh-air door to prevent outside air from entering the passenger compartment. The recirculation mode will cancel whenever defrost is requested. Pressing the Recirculation Switch while in defrost mode will illuminate the Recirculation Switch LED, but only while the button is pressed. Under this circumstance, the recirculation request will be denied and the fresh-air door will remain in the fresh position. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

A/C Switch
The A/C Switch is a momentary contact switch. Toggling the switch results in the A/C - Heater Control Module sending a change of state message to the PCM to provide A/C compressor clutch activation or deactivation respectively. The A/C - Heater Control Module will only provide this request if EVAP function is found acceptable. The Power Switch must be on to make the A/C switch active. The switch LED illuminates when the switch is ON. The A/C Switch setting is remembered during power down.

Blower Switch - Front
The rotary Blower Switch has five positions, Low, M1, M2, M3, and High. The Power Switch must be on to make the Blower Switch active. Toggling the Power Switch results in the A/C - Heater Control Module sending a request to the FCM to provide blower motor activation or deactivation respectively.

Blower Switch - Rear Blower Front Control Switch
The rotary Blower Switch has five positions, Rear, OFF; Low, Med, and High. The Power Switch must be on to make the Blower Switch active. The Blower Switch must be in the Rear position to make the Rear Blower Rear Control active. Toggling the Power Switch results in the A/C - Heater Control Module sending a request to the FCM to provide blower motor activation or deactivation respectively.

Blend Switch - Single Zone
The single, rotary Blend Switch has multiple detents to control the full range of temperature that the system can produce in any mode. Rotating the switch results in the A/C - Heater Control Module signaling the actuator to move the blend door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Blend Switch - Dual- and Three-Zone
The dual, sliding Blend Switches have multiple detents to control the full range of temperature that the system can produce in any mode. On Dual-Zone systems, the upper slide pot controls the driver-side blend door, while the lower slide pot controls the passenger-side blend door. On Three-Zone systems, the upper slide pot controls the driver-side blend door and, when activated, the Rear A/C - Heater Unit Blend Door. The lower slide pot controls the passenger-side blend door. Sliding the switch resuits in the A/C - Heater Control Module signaling the actuator to move the blend door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Mode Switch - Single- and Dual-Zone
The single, rotary Mode Switch has 13 detents to either direct airflow to the panel outlets, a mix of floor and panel outlets, floor outlets, a mix of floor and defrost outlets, or defrost outlets. Rotating the switch results in the A/C - Heater Control Module signaling the actuator to move the mode door. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Mode Switch - Three-Zone
The single, rotary Mode Switch has 13 detents to either direct airflow to the panel outlets, a mix of floor and panel outlets, floor outlets, a mix of floor and defrost outlets, or defrost outlets. When the Rear A/C - Heater Unit is activated, the Mode Switch also controls its Mode Door to direct the rear airflow to the floor or overheard outlets. Rotating the switch results in the A/C - Heater Control Module signaling the actuator to move the mode door(s). All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Rear Blower Rear Control
Switch Operation
The A/C - Heater Control Module's Power Switch must be ON to make the Rear Blower Front Control Switch active. The Rear Blower Front Control Switch must be in the Rear position to make the Rear Blower Rear Control active.

Blower Switch
The rotary Blower Switch has three positions, Low, Med, and High. Toggling the A/C - Heater Control Module's Power Switch on and positioning the Rear Blower Front Control Switch in the Rear position results in the A/C - Heater Control Module sending a request to the FCM to provide blower motor activation. Toggling the A/C - Heater Control Module's Power Switch off or rotating the Rear Blower Front Control Switch OFF of the Rear position results in the A/C - Heater Control Module sending a request to the FCM to provide blower motor deactivation.

Blend Switch
The rotary Blend Switch controls the full range of temperature that the rear system can produce in any mode. Rotating the switch results in the A/C - Heater Control Module signaling the actuator to move the blend door. A low temperature setting directs airflow to the overhead outlets, while a high temperature setting directs airflow to the floor outlets. All door positions are determined relative to the number of commutator pulses required to provide full travel of the door. On command, the A/C - Heater Control Module runs the actuator for the number of pulses corresponding to the desired door position.

Active And Stored Trouble Codes
The A/C-Heater Control Module is capable of storing Active and Stored trouble codes. An active code indicates that a fault exists in the system. A stored code indicates that a problem had occurred in the system, but is not currently present. Active codes cannot be erased until the problem causing the code has been repaired. At this time the Active code is converted to a Stored code, which can be erased using the DRBIII(R).