Part 2C
HEATING AND A/C SYSTEMS
A single-zone HVAC system is available on all JR series vehicles.
Manual Temperature Control
HVAC Control
The HVAC 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. 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.
Air Intake
When the fresh-air door is open, outside air is drawn into the HVAC housing through the cowl opening at the base of the windshield. When the fresh-air door is closed, recirculated air is drawn in to the HVAC housing from under the instrument panel.
Air Distribution
The HVAC unit has four fully adjustable instrument panel outlets. Side-window demister outlets in the instrument panel eliminate the need for door ducts and door-to-instrument panel seals. A single, central mounted outlet delivers air for defrosting the windshield. Two ducts, one on each side of the center console underneath the instrument panel, provide airflow to the driver floor area and the front seat passenger floor area.
A/C-heater Control, Switch Operation
Blower Switch
The rotary Blower Switch has five positions, OFF; Low, M1, M2, and High. Rotating the Blower Switch results in the A/C - Heater Control providing direct blower motor activation, change in blower speed, and blower motor deactivation respectively. The Blower Switch must be in any of the four ON positions to request A/C, and also to have the A/C - Heater Control send a signal to the Body Control Module to signal the door actuators to change door position.
Mode Switch
The rotary Mode Switch has a total of eight positions. The first three, for A/C request, include Recirc/Bi-level, Panel, and Bi-level. The remaining five positions, for Heat request, include Panel, Bi-level, Floor, Floor/Defrost, and Defrost. The Floor/Defrost position and the Defrost position also provided an A/C request.
Mode Switch, A/C Request
Provided that the Blower Switch is in any of the four ON positions, rotating the Mode Switch to any of the three A/C request positions, the Floor/Defrost position, or the Defrost position, will result in the A/C - Heater Control sending a signal to the BCM to send a message to the PCM to provide A/C compressor clutch activation. However, the BCM will only provide this request if EVAP function is found acceptable.
Mode Switch, Mode Door Position Change Request
Provided that the Blower Switch is in any of the four ON positions, rotating the Mode Switch will result in the A/C Heater Control sending a signal to the BCM to signal the actuator to move the mode door. A potentiometer, inside the Mode Door Actuator, and feedback circuits provide the BCM with door position information.
Mode Switch, Fresh-air Door Position Change Request
Provided that the Blower Switch is in any of the four ON positions, rotating the Mode Switch to the Recirc position will result in the A/C - Heater Control sending a signal to the BCM to signal the actuator to close the fresh-air door. While rotating the mode Switch to any other position results in the A/C - Heater Control sending a signal to the BCM to signal the actuator to open the fresh-air door. When the Blower Switch is OFF, the fresh-air door closes to prevent outside air from entering the passenger compartment.
Blend Switch
The rotary Blend Switch has multiple detents to control the full range of temperature that the system can produce in any mode. Provided that the Blower Switch is an any of the four ON positions, rotating the Blend Switch will result in the A/C - Heater Control sending a signal to the BCM to signal the actuator to move the blend door. A potentiometer, inside the Blend Door Actuator, and feedback circuits provide the BCM with door position information.
Rear Window Defogger Switch
The Rear Window Defogger Switch is a momentary contact switch. Toggling the switch results in the A/C - Heater Control sending a signal to the BCM to provide rear window defogger activation or deactivation respectively. The switch LED illuminates when the switch is ON.
Diagnostic Trouble Codes
All HVAC Diagnostic Trouble Codes are stored in the Body Control Module. Stored DTCs indicate that a problem has occurred in the HVAC system, and may still be present. To verify a problem is still present in the HVAC system, use the DRB III to erase all stored BCM DTCs. After erasing the DTC(s), use the DRB III to see if the DTC(s) reappear. If necessary, actuate the A/C - Heater Control switches with the ignition ON and with the engine running while monitoring the DRB III to see if the DTC(s) reappear.
INTERIOR LIGHTING
Courtesy Lamp Control
The body controller has direct control over the majority of the vehicle's courtesy lamps. The body computer will illuminate the courtesy lamps under any of the following conditions:
1. Any door is ajar.
2. The courtesy lamp switch ON the instrument panel is closed.
3. A Remote Keyless entry unlock message is received. If the interior lamps are left ON after the ignition is turned OFF, the BCM will turn them OFF after 15 minutes or until either the dome lamp switch or door ajar switch changes state.
Illuminated Entry
Illuminated entry will be initiated when the customer enters the vehicle by unlocking the doors with the key fob, or with the key if the vehicle is equipped with vehicle theft alarm. Upon exiting the vehicle, if the lock button is pressed with a door open, illuminated entry will cancel when the door closes. If the doors are closed and the ignition switch is turned ON, the illuminated entry also cancels.
MECHANICAL INSTRUMENT CLUSTER
The Mechanical Instrument Cluster (MIC) is divided into 4 sections. Primary gauges (Speedometer and Tachometer), secondary gauges (Fuel Level, Engine Coolant Temperature), PCI bus enabled indicator lamps and hardwired enabled indicator lamps.
The gauge mechanisms function in the same way. The main differences are in the face and size of the gauge.
The Oil Pressure, Brake Warning, Turn Signal and Fog Lamp indicators are directly wired to the circuits that they are indicators for. These indicators are located in, but not controlled by, the MIC and are not part of any MIC self test or diagnostic. All indicators are replaceable bulbs or LEDs.
The PCM sends a gauge position message to the BCM through the PCI bus. The MIC receives this message from the BCM, translates it, and positions the gauges. The BCM also sends messages to the MIC to actuate all PCI controlled indicators. These messages are received when the Ignition Switch is in the RUN or START position.
When the ignition Switch is turned to the RUN position, a bulb-check is performed. This consists of activating the PCI bus controlled indicators for approximately 2 to 4 seconds. By holding the TRIP/RESET button in while turning the Ignition Switch to the RUN position, you can activate the MIC Self Test.
The Following indicators are controlled by PCI bus messages:
- Malfunction Indicator Lamp
- Charging System Warning Indicator
- Engine Coolant Temperature Indicator
- Cruise Engaged Indicator
- Airbag Warning Indicator
- Low Fuel Indicator
- ABS Warning Indicator
- High Beam Indicator
The following indicators are hardwired and not controlled by PCI bus messages:
- Seat Belt Indicator
- Oil Pressure Indicator
- Brake Warning Indicator
- VTSS Indicator
- Turn Signal Indicators
- Fog Lamp Indicators
POWER DOOR LOCK SYSTEM
The door lock switches provide a variable amount of voltage through the Multiplexed (MUX) circuit to the BCM. Depending upon that input and various conditions that must be met (i.e. door lock inhibit, etc.), the BCM will determine the action to be taken and activate the proper relay for approximately 250 to 350 msec. If the vehicle is equipped with the vehicle theft security system it will have the central locking feature which locks and unlocks all doors from the cylinder lock switches. These switches are on separate multiplexed circuits to the BCM and have trouble codes relating to each of them.
RKE Remote Keyless Entry - This feature allows locking and unlocking of the vehicle door(s) by remote control using a hand-held transmitter (sometimes referred to as a fob) to activate a radio receiver (RKE module). This module now plugs into the body control module which is directly connected to the junction block. With this feature RKE can now be added to a non-equipped vehicle by installing a module. If the vehicle is equipped with the vehicle theft security system, RKE will also arm and disarm that system. A 4-button transmitter is used which provides lock, unlock, decklid release and panic features. Decklid release is only operable while the vehicle is in the park position. The module is capable of retaining up to 4 transmitter codes. Rolling code, which increases security, is also included in this system. If the transmitter goes out of synchronization it is easily put back in by pressing the lock button when the transmitter is within range. An external antenna has been added which plugs into the module to provide greater range. RKE will also turn ON the interior lamps when a valid unlock command is received and will extinguish the interior lamps when a lock command is received and all doors are closed.
Door Lock Inhibit - When the key is in the ignition and the driver front door is open, all door lock switches are disabled. The unlock switches are still functional. This protects against locking the vehicle with the keys still in the ignition.
Automatic (rolling) Door Locks - This feature can be enabled or disabled by using either the DRB III or the customer programmable method. When enabled, all doors will lock when the vehicle reaches a speed of 15 mph (24 km/h) and all doors are closed. If a door is opened and the vehicle slows to below 15 mph (24 km/h), the locks will operate again once all doors are closed and the speed is above 15 mph (24 km/h).
Decklid Release - Decklid release is now a function of the body control module. Trouble codes are provided to assist in the diagnosis of this system.
Customer programmable features are: Horn chirp, one or two press decklid release, programming a new transmitter (using a previously programmed transmitter), rolling door locks, unlock on exit, and RKE lamp flash.
POWER CONVERTIBLE TOP
Top Control
The body control module now controls all the functions of the convertible top. The body control module supplies a multiplexed voltage of approximately 90% of ignition voltage to the power top switch. Through a series of resistors the power top switch switches the circuit to ground depending on the position of the switch. The BCM then supplies the ground path for the up or down relay as requested. The power top switch has a 4.7-ohm diagnostic resistor that allows the BCM to detect a possible open circuit.
Window Drop Relay Assembly
The convertible has a new feature that allows the operator to lower all four windows and lower the top at the same time. This is accomplished by pressing the power top switch to the second detent. Through the multiplexed circuit of the power top switch the BCM will supply the ground for the window drop relay assembly.
The window drop relay assembly is comprised of four separate relays that are in series with the power window circuits. The relay assembly is located in the driver door.
VEHICLE COMMUNICATION
The Programmable Communication Interface multiplex system (PCI bus) consists of a single wire. The Body Control Module (BCM) acts as a splice to connect each module and the Data Link Connector (DLC) together. Each module is wired in parallel to the data bus through its PCI chip set and uses its local ground as the bus reference, The wiring is a minimum 20 gage.
The bus is designed to handle a maximum number of nodes to meet all of the bus load and timing requirements. The bus resistance and capacitance is designed to provide a maximum level of filtering without distorting the bus symbols. This is why extra capacitance and resistance should not be added to the PCI Data Bus circuitry.
In order for an electronic control module to communicate on the PCI data bus, the module must have bus interface electronics consisting of a transmitter/receiver (or transceiver) and Logic control, but termination for loading and filtering the bus, and wiring which interconnects the system.
Because of the unique coding scheme used in the PCI bus, each module is required to have logic control. The data moving on the bus is called symbols. The interface logic performs the following functions: encode and decodes binary data into symbols, synchronizes all bus symbol timing and edges, controls and the sending and receiving of messages, monitors for bus arbitration, monitors for corrupted symbols due to noise and controls the transceiver.
The bus logic control also provides the transceiver with the information it needs to transmit symbols on the bus. The transceiver controls the waveshaping of each symbol that it transmits by using internal voltage controlled current drivers. When the bus transceiver is turned ON, the bus driver ramps up the voltage to the set range and maintains this voltage until the driver is turned OFF; at which time the voltage is ramped back down to the low voltage, ground. The transceiver is designed to allow for arbitration between modules. If more than one module is trying to access the PCI bus at one time, the code determines the message that has the higher priority, and is then allowed to access the bus first.
The PCI bus requires a resistance and capacitance termination load to ground to operate. Because each bus transceiver can only source current to the bus, the resistance load is required to sink this current and pull the bus to ground on the falling edge of the symbols. The bus resistance is minimum of 315 ohms to a maximum of 2 K ohms. The termination capacitance is required for noise filtering and to help in the symbol wave shaping. The bus capacitance shall not be greater than 12,000 pf.
Each module on the PCI bus has a small termination load of a parallel resistance and capacitor to make up part of the overall bus termination load. One or two modules on the PCI bus may have a higher load termination to provide stabilizing influence over the variations of the vehicle builds. These modules, called dominant modules, may very for car line to car line. The Powertrain Control Module (PCM) and the body control module (BCM) are the dominant nodes for this vehicle.
Each module provides its own bias and termination in order to transmit and receive messages. The bus voltage is at zero volts when no modules are transmitting and is pulled up to about seven and a half volts when modules are transmitting. The bus messages are transmitted at a rate averaging 10800 bits per second. Since there is only voltage present when the modules transmit, and the message length is only about 500 milliseconds, it is ineffective to try and measure the bus activity with a conventional voltmeter. The preferred method is to use the DRB III lab scope. The 12 V square wave selection on the 20-volt scale provides a good view of the bus activity. Voltage on the bus should pulse between zero and about seven and a half volts. Refer to the following figure for some typical displays.
The PCI Bus failure modes are broken down into two categories. PCI Bus Communication Failure and individual module no response. Causes of a PCI Bus communication failure include a short to ground or to voltage on any PCI Bus circuit. individual module no response can be caused by an open circuit at the BCM or at the module, or an open battery or ground circuit to the affected module.
Symptoms of a complete PCI Bus communications failure would include but are not limited to:
- All gauges on the MIC stay at zero
- All Telltales on MIC illuminated
- MIC backlighting at full intensity
- No response received from any module on the PCI Bus through the DRB III (Except the PCM)
- No start (if equipped with sentry key immobilizer system)
Symptoms of individual module failure could include any one or more of the above. The difference would be that at least one or more modules would respond to the DRB III
Diagnosis starts with symptom identification. If a complete PCI Bus failure is suspected, begin by identifying which modules the vehicle is equipped with and then attempt to get a response from the modules with the DRB III. If any modules (except PCM) are responding, the failure is not related to the total bus, but can be caused by one or more modules PCI Bus circuit or power supply and ground circuits. The DRB III may display "BUS +/- SIGNAL OPEN" or "NO RESPONSE" to indicate a communication problem. These same messages will be displayed if the vehicle is not equipped with that particular module. The CCD error message is a default message used by the DRB III and in no way indicates whether or not the PCI Bus is operational. The message is only an indication that a module is either not responding or the vehicle is not equipped with that particular module.
NOTE: COMMUNICATION OVER THE BUS IS ESSENTIAL TO THE PROPER OPERATION OF THE VEHICLES ON-BOARD DIAGNOSTIC SYSTEMS AND THE DRB III. PROBLEMS WITH THE OPERATION OF THE BUS OR DRB III MUST BE CORRECTED BEFORE PROCEEDING WITH DIAGNOSTIC TESTING. IF THERE IS A PROBLEM, REFER TO THE COMMUNICATIONS CATEGORY.
Bus Failure Message
Odometer Displays "No Bus" - The Mechanical Instrument Cluster (MIC) cannot communicate over the bus and does not know why.
VEHICLE THEFT SECURITY SYSTEM
This passive system is designed to protect against vehicle theft. The vehicle theft security system (VTSS) is part of the body control module (BCM), which monitors vehicle doors and the ignition for unauthorized operation. The alarm activates by sounding the horn, flashing the headlamps, courtesy lamps, and the VTSS indicator lamp. Passive arming occurs upon normal vehicle exit by turning the ignition OFF, opening the driver's door, locking the doors with the power lock, and closing the driver's door or locking the doors with RKE. Manual arming occurs by using the key to lock the doors after closing them. The indicator lamp in the instrument cluster will flash for 15 seconds, showing that arming is in progress. If no monitored systems are activated during this period, the system will arm and the indicator will flash at a slow rate. If the indicator lamp remains steadily lit during the arming process, this can indicate a loss of decklid cylinder lock switch. When something triggers the alarm, the system will signal the headlamps, courtesy lamps, and horn for about 3 minutes, then headlamps for an additional 15 minutes if the offending input is still present.
For complaints about the Theft Alarm going OFF on its own use the DRB III and select "Body Computer" then "Input/Output Display" and read the "Last VTSS Cause" status.
Tamper Alert - The VTSS indicator lamp will flash twice quickly and the horn will chirp three times when the system is disarmed to indicate a tamper condition has occurred.
Manual Override - The system will not arm if the doors are locked using the manual lock control (by hand) or if the locks are actuated by an inside occupant after the door is closed.
To verify the system, proceed as follows:
1. Open the driver's door.
2. Remove the ignition key (but keep it in hand).
3. Lock the doors with the power lock switch or the RKE.
4. Close the driver's door.
NOTE: After the doors are closed, locking the doors with RKE will also arm the system.
NOTE: If the VTSS indicator lamp flashed, the system is operational and verified. If not, there may be a problem with the system.
Arming/Disarming - Active arming occurs when the remote keyless entry transmitter is used to lock the vehicle doors, whether the doors are open or closed. If one or more doors are open the arming sequence is completed only after all doors are closed.
Passive disarming occurs upon normal vehicle entry (unlocking either front door with the key). This disarming also will halt the alarm once it has been activated.
Active disarming occurs when the remote keyless entry transmitter is used to unlock the vehicle doors. This disarming also will halt the alarm once it has been activated.
System Self-Tests - NOTE: System self tests can be entered only with the DRB III.
NOTE: A Powertrain Control Module from a vehicle equipped with a vehicle theft security system cannot be used in a vehicle that is not equipped with a vehicle theft security system. If the VTSS indicator lamp comes ON after ignition ON and stays ON, the PCI bus communication with the Powertrain Control Module possibly has been lost.
WIPER SYSTEM
The wiper system provides the driver with the normal wiper (low and high speeds), intermittent wipe, and wipe after wash. The driver selects the wiper function via the resistive multiplexed stalk switch mounted on the steering column. The BCM uses the input signal from the wiper stalk switch, wiper motor park switch, and the washer switch to control the wiper system. The Body Control Module (BCM) then controls the relays and timing functions to provide the driver selected features.
Speed Sensitive Intermittent Wipe Mode
There are 6 individual delay times with a minimum delay of 1/2 second to a maximum of 18 seconds. When the vehicle speed is under 10 mph (6 km/h), the delay time is doubled providing a range of 1 second to 36 seconds.
Park after Ignition OFF
Because the wiper relays are powered from the battery the BCM can run the wipers to park after the ignition is turned OFF.
Wipe after Wash
When the driver presses the wash button for over 1/2 second and then releases it, the wiper will continue to run for 2 additional wipe cycles.
The wiper system utilizes the BCM to control the ON/OFF and hi/low relays fro low and hi speed wiper functions, intermittent wiper delay as the switch position changes, pulse wipe, wipe after wash mode, and wiper motor park functions. The BCM uses the vehicle speed input to double the usual delay time below 10 mph (17 km/h).
WARNINGS
VEHICLE DAMAGE WARNINGS
Before disconnecting any control module, make sure the ignition is "OFF". Failure to do so could damage the module.
When testing voltage or continuity at any control module, use the terminal side (not the wire end) of the connector. Do not probe a wire through the insulation; this will damage it and eventually cause it to fail because of corrosion.
Be careful when performing electrical tests so as to prevent accidental shorting of terminals. Such mistakes can damage fuses or components. Also, a second DTC could be set, making diagnosis of the original problem more difficult.
ROAD TEST COMPLAINT VEHICLE
Some complaints will require a test drive as part of the repair verification procedure. The purpose of the test drive is to try to duplicate the diagnostic DTC or symptom condition.
WARNING: BEFORE ROAD TESTING A VEHICLE, BE SURE THAT ALL COMPONENTS ARE REASSEMBLED DURING THE TEST DRIVE, DO NOT TRY TO READ THE DRB III SCREEN WHILE IN MOTION. DO NOT HANG THE DRB III FROM THE REAR VIEW MIRROR OR OPERATE IT YOURSELF. HAVE AN ASSISTANT AVAILABLE TO OPERATE THE DRB III.
REQUIRED TOOLS AND EQUIPMENT
DRB III (diagnostic read-out box)
Jumper wires
Ohmmeter
Voltmeter
Sentry Key Tester
Test Light
8310 Airbag System Load Tool
8443 SRS Airbag System Load Tool
GLOSSARY OF TERMS
ABS Antilock brake system
ACM Airbag control module
AECM Airbag electronic control module (ACM)
ASDM Airbag system diagnostic module (ACM)
BCM Body control module
CAB Controller antilock brake
CMTC Compass/mini-trip computer
DAB Driver airbag
DLC Data link connector
DTC Diagnostic trouble code
DR Driver
EBL Electric back lite (rear window defogger)
HVAC Heater ventilation, air conditioning
MIC Mechanical instrument cluster
MTC Manual temperature control
OBD On board diagnostics
ODO Odometer
ORC Occupant restraint controller (ACM)
PAB Passenger airbag
PASS Passenger
PCI Programmable Controller Interface (vehicle communication bus)
PCM Powertrain control module
PDC Power distribution center
PWM Pulse width modulated
RKE Remote keyless entry
SAB Seat airbag
SBT Seat belt tensioner
SIACM Side impact airbag control module
SKIM Sentry key immobilizer module
SKIS Sentry key immobilizer system
SQUIB Also called initiator (located inside airbag)
SRS Supplemental restraint system
TCM Transmission control module
VFD Vacuum fluorescent display
VTSS Vehicle theft security system