POWERTRAIN CONTROL MODULE (PCM)
The PCM is a digital computer that controls ignition system, air/fuel ratio, emission control devices, cooling fan, charging system, idle speed, and cruise control system (if equipped). PCM uses input signals from various switches and sensors to control output devices in order to achieve optimum engine performance for all operating conditions. See INPUT DEVICES and OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS. Powertrain Control Module (PCM) is located between driver's side front fender and power distribution center, near battery. (Scheme 1)
PCM contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if a electronic control system failure exists. DTC may be retrieved from PCM for system diagnosis by using a scan tool or Malfunction Indicator Light (MIL). See SELF-DIAGNOSTIC SYSTEM.
Scheme 1
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the PCM. The second category covers OUTPUT SIGNALS, which are components controlled by the PCM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS - 2.4L article. The available input signals include the following
A/C PRESSURE SENSOR
A/C pressure sensor may also be referred to as A/C pressure switch or A/C pressure transducer. A/C pressure sensor provides input signal to Powertrain Control Module (PCM) to indicate A/C system pressure. The PCM uses input signal for controlling A/C compressor clutch. If pressure is too low, PCM will not engage A/C compressor clutch. If pressure is too high, PCM will disengage A/C compressor clutch and turn on cooling fans to prevent the A/C compressor head pressure from becoming excessive. The A/C pressure sensor is located on A/C refrigerant line on firewall, near front of generator and contains a Gray 4-pin connector.
A/C SWITCH
When A/C switch is in ON position, input signal is delivered from A/C switch to Powertrain Control Module (PCM) to indicate A/C operation has been requested. The PCM uses input signal for cycling A/C compressor clutch by controlling ground circuit on A/C clutch relay. The PCM also uses input signal to increase engine idle speed to compensate for the increased engine load. The A/C switch is located on heating and A/C control panel at center of instrument panel, near the stereo. The A/C clutch relay is located in power distribution center in engine compartment, near the battery.
AUTO SHUTDOWN (ASD) RELAY
A 12-volt input signal is delivered from ASD relay to Powertrain Control Module (PCM) when ASD relay is energized. If PCM does not receive a 12-volt input signal when ASD relay is energized, a Diagnostic Trouble Code (DTC) will be stored in PCM. ASD relay is located in power distribution center in engine compartment, near the battery. Auto Shutdown (ASD) relay may also be referred to as Automatic Shutdown (ASD) relay.
BATTERY VOLTAGE
Powertrain Control Module (PCM) monitors battery voltage to determine fuel injector pulse width. If battery voltage is not within specified range, PCM will increase fuel injector pulse width.
BRAKE SWITCH
Brake switch delivers input signal to Powertrain Control Module (PCM) to indicate when brakes are applied. PCM uses input signal for controlling cruise control system and idle speed. Brake switch is located near top of brake pedal and may also be referred to as brakelight switch.
CAMSHAFT POSITION SENSOR
Camshaft position sensor may be referred to as Camshaft Position (CMP) sensor. Camshaft position sensor is located on rear of cylinder head, just below valve cover. A target magnet attaches to rear of camshaft and uses locating dowels for proper positioning. (Scheme 2) As target magnet rotates, camshaft position sensor senses the change in the polarity. The polarity change causes camshaft position sensor output voltage to switch from high-voltage of 5 volts to a low-voltage of.3 volt. Camshaft position sensor delivers input signal to Powertrain Control Module (PCM). PCM uses this input signal along with input signal from crankshaft position sensor for determining crankshaft position for fuel injection synchronization and cylinder identification.
Scheme 2
CRANKSHAFT POSITION SENSOR
Crankshaft position sensor may be referred to as Crankshaft Position (CKP) sensor. Crankshaft position sensor is located on cylinder block, behind generator, near oil filter. Crankshaft contains a crankshaft pulse ring which contains 2 sets of notches ground into the No. 2 counterweight.
As crankshaft rotates, crankshaft position sensor generates pulses due to notch areas on the No. 2 counterweight. When solid area on crankshaft pulse ring aligns with bottom of crankshaft position sensor, voltage decreases to less than .3 volt. When notch area on crankshaft pulse ring aligns with bottom of crankshaft position sensor, voltage increases to 5 volts. Switching of the voltage generates pulses. These pulses provide an input signal to the Powertrain Control Module (PCM). PCM uses input signal to determine crankshaft position. PCM uses input signal along with other various input signals for controlling fuel injector pulse width, ignition system and engine idle speed.
CRUISE CONTROL SYSTEM SWITCHES
Cruise control system switches are located at center of steering wheel. Cruise control system switches provide 5 different input signals to Powertrain Control Module (PCM) for controlling speed control system.
ON/OFF switch provides input signal to PCM to indicate that cruise control system has been activated or deactivated. SET switch provides input signal to PCM to indicate that a set vehicle speed has been selected. RESUME switch provides input signal to PCM to indicate that previous fixed speed is requested. CANCEL switch provides input signal to PCM to deactivate cruise control system, but retain the set speed in memory. PCM uses these inputs to control cruise control servo.
DATA LINK CONNECTOR
Data Link Connector (DLC) provides an input signal to Powertrain Control Module (PCM) when using scan tool to retrieve Diagnostic Trouble Codes (DTCs) from PCM. Input signal may also be used when performing various tests on the PCM and electronic control system.
DOWNSTREAM OXYGEN SENSOR
Downstream oxygen sensor is a heated oxygen sensor mounted on exhaust pipe behind catalytic converter. Heater is used on downstream oxygen sensor so sensor reaches operating temperature quicker and maintains sensor at operating temperature during all operating modes. Heater on downstream oxygen sensor receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS.
Downstream oxygen sensor produces a small electrical voltage input signal to Powertrain Control Module (PCM) depending on amount of oxygen content in the exhaust gas. Downstream oxygen sensor produces a low voltage when a large amount of oxygen exists in exhaust gas (lean condition) and a higher voltage when a lesser amount of oxygen exists in exhaust gas (rich condition).
PCM uses input signal for controlling air/fuel ratio. Also as catalytic converter deteriorates, input signal from downstream oxygen sensor begins to match input signal from upstream oxygen sensor except for a slight time delay. PCM compares input signals from upstream and downstream oxygen sensors to calculate efficiency of catalytic converter. If efficiency of catalytic converter becomes less than specified value, a DTC will be stored in PCM.
ENGINE COOLANT TEMPERATURE SENSOR
Engine Coolant Temperature (ECT) sensor delivers input signal to Powertrain Control Module (PCM) to indicate engine coolant temperature. PCM uses input signal for controlling air/fuel ratio, ignition system, idle speed and cooling fan operation. Engine coolant temperature sensor is located near thermostat housing and contains a Black/Light Blue wire and a Tan/Black wire in the connector.
INTAKE AIR TEMPERATURE SENSOR
Intake air temperature delivers input signal to Powertrain Control Module (PCM) to indicate temperature of incoming intake air. PCM uses input signal for controlling fuel injector pulse width and spark advance. Intake air temperature sensor is screwed into rear of intake manifold, near cylinder head and contains a Gray 2-pin connector.
KNOCK SENSOR
Knock delivers input signal to Powertrain Control Module (PCM) when a knock is detected on one of the cylinders. As the intensity of the knock increases, the knock sensor input signal voltage to the PCM increases. PCM uses input signal and retards ignition timing according to strength of input signal from knock sensor. knock sensor is located on cylinder block, below intake manifold, near rear of generator and oil dipstick tube.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
PCM delivers a 5-volt supply voltage to MAP sensor. MAP sensor monitors intake manifold vacuum and delivers an input signal to Powertrain Control Module (PCM). When intake manifold vacuum increases, MAP sensor input signal voltage to PCM decreases proportionately. When intake manifold vacuum decreases, MAP sensor input signal voltage to PCM increases proportionately. PCM uses input signal from MAP sensor along with other input signals for controlling ignition system and air/fuel ratio.
MAP sensor is located on end of intake manifold, near oil filler cap on valve cover, just above fuel rail and contains a 3-pin connector.
PARK/NEUTRAL SWITCH (A/T MODELS)
On 3-speed models, park/neutral switch is located on side of transaxle. (Scheme 3) On 4-speed models, park/neutral switch is located on side of transaxle and may be referred to as transmission range sensor. (Scheme 4) On all models, park/neutral delivers input signal to Powertrain Control Module (PCM) to indicate transaxle gear selection. PCM uses input signal for controlling idle speed and ignition system.
Scheme 3
Scheme 4
THROTTLE POSITION SENSOR
Throttle Position (TP) sensor is mounted on throttle body and delivers input signal to Powertrain Control Module (PCM) to indicate throttle position. TP sensor input signal will vary from approximately .5 volt at idle position to approximately 4.5 volts at full throttle. PCM uses input signal along with other various input signals for controlling fuel injector pulse width and ignition system.
TRANSMISSION CONTROL MODULE (4-SPEED A/T)
Transmission Control Module (TCM) provides input signal to Powertrain Control Module (PCM) to indicate vehicle speed. TCM calculates vehicle speed based upon input signal from output speed sensor and speedometer pinion factor. The PCM uses input signal along with TP sensor closed throttle input signal to determine if a closed throttle deceleration or normal idle condition exists. During deceleration, PCM controls Idle Air Control (IAC) motor to maintain a desired MAP value. During idle conditions, PCM controls IAC motor to maintain a desired idle speed. The TCM is located on passenger's side front corner of engine compartment, on inner fender, near windshield washer reservoir. (Scheme 5)
Scheme 5
TRANSMISSION RANGE SENSOR (4-SPEED A/T)
Transmission range sensor may also be referred to as park/neutral switch. See PARK/NEUTRAL SWITCH (A/T MODELS).
UPSTREAM OXYGEN SENSOR
Upstream oxygen sensor is a heated oxygen sensor mounted on the exhaust manifold. Heater is used on upstream oxygen sensor so sensor reaches operating temperature quicker and maintains sensor at operating temperature during all operating modes. Heater on upstream oxygen sensor receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS.
Upstream oxygen sensor produces a small electrical voltage input signal to PCM depending on amount of oxygen content in the exhaust gas. Upstream oxygen sensor produces a low voltage when a large amount of oxygen exists in exhaust gas (lean condition) and a higher voltage when a lesser amount of oxygen exists in exhaust gas (rich condition). PCM uses input signal for controlling fuel injector pulse width for controlling the air/fuel ratio.
VEHICLE SPEED SENSOR (3-SPEED A/T)
Vehicle Speed Sensor (VSS) delivers input signal to Powertrain Control Module (PCM) to indicate transaxle output shaft speed. PCM uses input signal from VSS, along with TP sensor closed throttle input signal to determine if a closed throttle deceleration or normal idle condition exists. During deceleration, PCM controls Idle Air Control (IAC) motor to maintain a desired MAP value. During idle conditions, PCM controls IAC motor to maintain a desired idle speed. Vehicle speed sensor is mounted on extension housing for passenger's side axle shaft at firewall side of transaxle. (Scheme 6)
Scheme 6
OUTPUT SIGNALS
Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to the system indicated after component.
A/C CLUTCH RELAY
See RELAYS under MISCELLANEOUS CONTROLS.
See RELAYS under MISCELLANEOUS CONTROLS.
FUEL PUMP RELAY
See FUEL DELIVERY under FUEL SYSTEM.
See DATA LINK CONNECTOR under SELF-DIAGNOSTIC SYSTEM.
DISTRIBUTORLESS IGNITION SYSTEM
See DISTRIBUTORLESS IGNITION SYSTEM under IGNITION SYSTEM.
EVAP PURGE SOLENOID
See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION SYSTEMS.
FUEL INJECTORS
See FUEL CONTROL under FUEL SYSTEM.
FUEL PUMP
See FUEL DELIVERY under FUEL SYSTEM.
See FUEL DELIVERY under FUEL SYSTEM.
GENERATOR FIELD
See GENERATOR under MISCELLANEOUS CONTROLS.
IDLE AIR CONTROL MOTOR
See IDLE SPEED under FUEL SYSTEM.
LEAK DETECTION PUMP
See EVAPORATIVE (EVAP) EMISSIONS SYSTEM under EMISSION SYSTEMS.
MALFUNCTION INDICATOR LIGHT (MIL)
See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.
RADIATOR FAN CONTROL RELAY
See RELAYS under MISCELLANEOUS CONTROLS.
SPEED CONTROL SERVO
See CRUISE CONTROL SYSTEM under MISCELLANEOUS CONTROLS.
STARTER RELAY
See RELAYS under MISCELLANEOUS CONTROLS.
TACHOMETER
See TACHOMETER under MISCELLANEOUS CONTROLS.
See TRANSMISSION under MISCELLANEOUS CONTROLS.
Fuel pump is a in-tank pump mounted at the bottom of fuel pump module on top of fuel tank. Fuel pump module also contains fuel pressure regulator and fuel level sensor for fuel gauge. (Scheme 7) Fuel pump is a positive displacement, immersible pump with a permanent magnet electric motor. Fuel is drawn through inlet strainer on bottom of fuel pump module, through fuel pressure regulator, fuel filter, and delivered to fuel rail and fuel injectors. Fuel pump contains an internal check valve in the pump outlet. Check valve is used to maintain fuel pressure when engine and fuel pump are not operating. Fuel pump is operated by voltage supplied from fuel pump relay.
Scheme 7
Fuel pump relay is used to provide voltage to fuel pump. Fuel pump relay is located in power distribution center in engine compartment, near the battery. (Scheme 1)
Fuel pump relay receives constant battery voltage at one side of relay from fuse No. 13 (20-amp) in power distribution center. When ignition is on, fuel pump relay receives voltage at the other side of the relay from Positive Temperature Coefficient (PTC) No. 1 in junction block located behind driver's side of instrument panel, to the left of steering column. PTC is a specified amperage solid-state circuit breaker. The Powertrain Control Module (PCM) controls the ground circuit for fuel pump relay. When ignition is on, PCM completes ground circuit for fuel pump relay and voltage is supplied to the fuel pump. If crankshaft position sensor does not detect engine rotation, the PCM opens the ground circuit and de-energizes the fuel pump.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is a nonadjustable in-tank pressure regulator mounted on fuel pump module on top of fuel tank. (Scheme 7) Fuel pressure regulator is a mechanical device used to maintain a constant fuel pressure at the fuel injectors. Fuel pressure regulator consists of a diaphragm, calibrated spring and a fuel return valve. Calibrated spring pushes downward on the diaphragm and closes off the fuel return valve. Fuel pressure is determined by amount of fuel pressure required to open the fuel return valve. When fuel return valve opens, excess fuel is returned to the fuel tank.
ASD relay provides voltage to fuel injectors. See RELAYS under MISCELLANEOUS CONTROLS.
Fuel injectors are electric solenoid valves controlled by Powertrain Control Module (PCM). Auto Shutdown (ASD) relay provides voltage to one side of fuel injector. The PCM initially energizes all fuel injectors at the same time at start up by completing ground circuit for each fuel injector. When fuel injector is energized, the armature and needle inside fuel injector move a short distance against spring, allowing fuel to be delivered in a fine atomized spray.
Once PCM determines crankshaft position, PCM energizes fuel injectors in sequence by controlling ground circuit for each fuel injector. This is referred to as sequential fuel injection. The PCM uses various input signals to determine the length of time fuel injector is energized (pulse width) by switching on and off the ground circuit for each fuel injector.
Idle Air Control (IAC) motor is mounted on throttle body. The Powertrain Control Module (PCM) controls idle speed by use of IAC motor to compensate for engine load or ambient temperatures. IAC motor is also used to prevent a deceleration engine stall by increasing the airflow when throttle is suddenly closed at a driving speed.
When PCM operates IAC motor, the pintle on IAC motor moves inward and outward. Movement of the pintle controls amount of air entering air by-pass passage on throttle body to regulate the idle speed. PCM uses input signals from A/C switch, brake switch, crankshaft position sensor, engine coolant temperature sensor, park/neutral switch and throttle position sensor for controlling idle speed.
A Distributorless Ignition System (DIS) is used to provide ignition spark and ignition timing. DIS is controlled by Powertrain Control Module (PCM). Ignition timing is controlled by PCM and is nonadjustable. DIS consists of camshaft position sensor, crankshaft position sensor, ignition coil, spark plug wires and spark plugs.
Ignition coil receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS. PCM uses input signal from camshaft position sensor, crankshaft position sensor, engine coolant temperature sensor, intake air temperature sensor, knock sensor and throttle position sensor for controlling ignition system and ignition timing. For operation of camshaft position sensor, crankshaft position sensor, engine coolant temperature sensor, intake air temperature sensor, knock sensor and throttle position sensor, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
CRANKCASE VENT SYSTEM
Crankcase vent system provides filtered air to vent the crankcase. Filter air for venting of crankcase is drawn in through resonator assembly located between air cleaner and throttle body.
EVAPORATIVE (EVAP) EMISSIONS SYSTEM
The EVAP system prevents fuel tank vapors from entering the atmosphere. EVAP system consists of EVAP canister, EVAP purge solenoid, leak detection pump, fuel tank pressure release/rollover valve and a pressure/vacuum type fuel tank cap. EVAP canister is located on frame rail, directly below the driver's seat. (Scheme 8) EVAP purge solenoid is located near passenger's side strut tower. (Scheme 9) Leak detection pump is located below driver's side of steering gear, above engine cradle. (Scheme 10) Fuel tank pressure release/rollover valve is located on fuel tank filler tube, just below fuel tank cap.
Pressure/vacuum type fuel tank cap seals filler tube on fuel tank so vapors cannot be released from fuel tank. Fuel tank cap contains check valves that prevent excessive pressure or vacuum in the fuel tank. Fuel tank vapors pass through vent hoses to EVAP canister, where the EVAP canister temporarily stores the fuel tank vapors. When certain operating conditions exist, the Powertrain Control Module (PCM) energizes EVAP purge solenoid, allowing intake manifold to draw fuel vapors at predetermined levels from EVAP canister, through throttle body and into the combustion chambers. PCM will not energize EVAP purge solenoid during cold start warm-up periods and hot starts. PCM varies amount of vapor flow according to engine operating conditions by controlling the pulse width (time solenoid is energized) for EVAP purge solenoid.
Leak detection pump is used to detect a leak in EVAP system and seals EVAP system so leak detection test may be performed. Leak detection pump consists of pump solenoid, a pump incorporating a switch which monitors the pump movement, 2 check valves, spring diaphragm and a EVAP canister vent valve. Immediately after a cold start with ambient temperature of 40-90°F (4.4-32°C) and engine coolant temperature is within 10°F (-12°C) of ambient temperature, leak detection pump solenoid is energized. When solenoid is energized, engine vacuum enters leak detection pump and draws the spring diaphragm upward, allowing atmospheric pressure to enter cavity on leak detection pump.
When leak detection pump solenoid is de-energized, this vents engine vacuum, allowing spring diaphragm to move downward, forcing the air out of cavity on leak detection pump and into the vent system. When leak detection pump solenoid is energized and de-energized, the cycle is repeated, resulting in a pumping effect. After passing leak detection phase of the test, system pressure is maintained until purge system is activated, in effect creating a leak. If cycle rate increases due to the flow of the purge system, the test is passed and diagnostic test is complete. If a leak is detected in EVAP system, a Diagnostic Trouble Code (DTC) will be stored in the PCM.
Scheme 8
Scheme 9
Scheme 10
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system is used to remove crankcase blow-by gases from crankcase by using a PCV valve and manifold vacuum. Crankcase blow-by gases are drawn through PCV and then returned back into the intake manifold with incoming air/fuel mixture.
The Data Link Connector (DLC) is a 16-pin connector located below driver's side of instrument panel. The Powertrain Control Module (PCM) contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if a electronic control system failure exists. DTC may be retrieved from PCM for system diagnosis by using Data Link Connector (DLC) and a scan tool. The DLC also provides a means to communicate with various vehicle control modules, check system operating conditions and to operate various system components. For additional information on using DLC and scan tool usage, see appropriate article TESTS W/CODES - 2.4L article.
MALFUNCTION INDICATOR LIGHT
The Malfunction Indicator Light (MIL) is located on instrument panel just below fuel gauge. When ignition is first turned on, MIL should come on and remain on for 3 seconds to verify bulb and circuit operation, and then go off. The Powertrain Control Module (PCM) contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if an electronic control system failure exists. When DTC is stored in PCM, the PCM will turn on the MIL and MIL will remain on steady. The MIL may be used to obtain DTC for system diagnosis. For additional information on MIL operation and usage, see TESTS W/CODES - 2.4L article.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
The A/C clutch relay is located in power distribution center in engine compartment, near the battery. (Scheme 1) The Powertrain Control Module (PCM) controls cycling of A/C compressor clutch by controlling ground circuit on A/C clutch relay. A/C clutch relay receives constant battery voltage at one side of relay from fuse No. 18 (5-amp) in power distribution center. When ignition is on, A/C clutch relay receives voltage at the other side of the relay from Positive Temperature Coefficient (PTC) No. 1 in junction block located behind driver's side of instrument panel, to the left of steering column. PTC is a specified amperage solid-state circuit breaker.
The PCM controls the ground circuit for A/C clutch relay. When ignition is on, PCM completes ground circuit for A/C clutch relay and A/C clutch relay provides voltage to A/C compressor clutch. The PCM controls cycling of A/C compressor clutch by controlling ground circuit on A/C clutch relay. When PCM senses low idle speed or full throttle, PCM opens the ground circuit and A/C clutch relays opens, shutting off A/C compressor clutch.
The ASD relay is located in power distribution center in engine compartment, near the battery. (Scheme 1) ASD relay provides battery voltage to fuel injectors, generator, ignition coil and heater on upstream and downstream oxygen sensors. ASD relay receives constant battery voltage at one side of relay from buss bar in power distribution center and fuse No. 12 (20-amp) in power distribution center.
The Powertrain Control Module (PCM) controls the ground circuit for ASD relay. When ignition switch is in OFF position, PCM will open ground circuit for ASD relay unless a heater monitor is being performed on oxygen sensors. When ignition switch is in ON or START position, PCM monitors crankshaft position sensor and camshaft position sensor input signals to determine engine speed and ignition timing. If input signals are obtained, PCM completes ground circuit and ASD relay is energized. If input signals are not received, PCM will not complete ground circuit for ASD relay. When ground circuit is completed and ASD relay is energized, a 12-volt input signal is delivered from ASD relay to PCM when ASD relay is energized. If PCM does not receive a 12-volt input signal when ASD relay is energized, a Diagnostic Trouble Code (DTC) will be stored in PCM.
Radiator fan control relay may be referred to as radiator fan relay. Radiator fan control relay controls operation of radiator cooling fans. Radiator cooling fans will operate at variable speeds depending on engine coolant temperature and the A/C system pressure. Radiator fan control relay is located near driver's side frame rail and air cleaner lower mount. (Scheme 11)
Radiator fan control relay receives constant battery voltage from fuse No. 4 (40-amp) in power distribution center. The Powertrain Control Module (PCM) controls the ground circuit for radiator fan control relay by using a pulsed (time on) ground. This pulsed ground is known as Pulse Width Modulated (PWM) ground. The PWM ground causes radiator cooling fan relay to produces a proportional output voltage for operating radiator cooling fans at different speeds.
Radiator cooling fans operate at high speed when engine coolant temperature is approximately 225°F (107°C) and then reduces to low speed when engine coolant temperature decreases to approximately 214°F (101°C). Radiator cooling fans will turn off when engine coolant temperature decreases to approximately 199°F (93°C). Also, when the A/C pressure sensor closes at approximately 275-295 psi (19.3-20.7 kg/cm 2 ), radiator cooling fans operate at high speed. When A/C pressure decreases approximately 40 psi (2.3 kg/cm 2 ), A/C pressure sensor opens and radiator cooling fans operate at low speed.
Scheme 11
Starter relay is located in power distribution center in engine compartment, near the battery. (Scheme 1) Starter relay provides battery voltage to solenoid on starter motor for starter operation. A double start override feature is used on the starting system to prevent starter from operating if engine is already running.
Starter relay receives constant battery voltage at one side of relay from fuse No. 5 (40-amp) in power distribution center. When ignition is in START position, starter relay receives voltage at the other side of the relay from Positive Temperature Coefficient (PTC) No. 10 in junction block located behind driver's side of instrument panel, to the left of steering column. PTC is a specified amperage solid-state circuit breaker. The Powertrain Control Module (PCM) provides the ground circuit to energize starter relay. When starter relay is energized, PCM monitors engine RPM and will remove the ground circuit once engine RPM has obtained a predetermined RPM. This prevents starter from operating if engine is already running.
GENERATOR
The Powertrain Control Module (PCM) uses various input signals and an internal electronic voltage regulator to maintain charging system voltage at 12.9-15.0 volts. Internal electronic voltage regulator controls charging system voltage by cycling the ground circuit on the generator field. Battery voltage is supplied to generator through a fusible link and the Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS. If a failure exists in the charging system, a Diagnostic Trouble Code (DTC) will be stored in the PCM.
CRUISE CONTROL SYSTEM
The Powertrain Control Module (PCM) controls ground circuit to vacuum and vent solenoids in speed control servo for controlling the cruise control system. When PCM completes the ground circuit to vacuum and vent solenoids in speed control servo, throttle is opened, and when ground circuits are open, throttle is closed. PCM balances the vacuum and vent solenoid operation to maintain the set vehicle speed. If a failure exists in the cruise control system, a Diagnostic Trouble Code (DTC) will be stored in the PCM.
The Powertrain Control Module (PCM) supplies engine RPM to tachometer on instrument panel through the twisted wire CCD Bus.
The Powertrain Control Module (PCM) and Transmission Control Module (TCM) supply various information between each other through the twisted wire CCD Bus. This information is used for operating the transmission and electronic engine controls. The TCM is located on passenger's side front corner of engine compartment, on inner fender, near windshield washer reservoir. (Scheme 5)