charging CHEVROLET DYNASTY 1993 Repair Manual

mode, the PCM compensates for the failure of certain
components that send incorrect signals. The PCM
substitutes for the incorrect signals with inputs from
other sensors and by using stored default values.Signals that can trigger the Malfunction Indi-
cator (Check Engine) Lamp.
² An emission system component
² Battery Voltage Input
² Charging system
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Methanol Concentration Sensor
² Throttle Position Sensor
The malfunction indicator lamp can also display
diagnostic trouble codes. Cycle the ignition switch on,
off, on, off, on, within five seconds and the PCM
displays any diagnostic trouble codes stored in
memory. Refer to the 2.5L Flexible Fuel Multi-Port
Fuel InjectionÐOn Board Diagnostics section in this
group for diagnostic trouble code descriptions.
RADIATOR FAN RELAYÐPCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The PCM grounds the radiator
fan relay when engine coolant reaches a predetermined
temperature. For more information, refer to Group 7,
Cooling Systems. The radiator fan relay is mounted on the drivers side
fender well, next to the strut tower (Fig. 11).
SPEED CONTROL SOLENOIDSÐPCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the PCM
supplies a ground only to the vent solenoid, the throttle
blade holds position. When the PCM removes the
ground from both the vacuum and vent solenoids, the
throttle blade closes. The PCM balances the two sole-
noids to maintain the set speed. Refer to Group 8H for
speed control information.
TACHOMETERÐPCM OUTPUT
The PCM supplies engine RPM to the instrument
panel tachometer. Refer to Group 8 for tachometer
information.
TORQUE CONVERTER CLUTCH SOLENOIDÐPCM
OUTPUT
Three-speed automatic transaxles use a torque con-
verter clutch solenoid. The PCM controls the lock-up of
the torque convertor through the solenoid. The tran-
saxle is locked up only in direct drive mode. Refer to
Group 21 for transaxle information.
MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to the output devices. For example, the PCM must calculate a different injector pulse
width and ignition timing for idle than it does for wide
open throttle (WOT). There are several different modes
of operation that determine how the PCM responds to
the various input signals. There are two different areas of operation, Open
Loop and Closed Loop. During Open Loop modes, the PCM receives input
signals and responds according to preset PCM pro-
gramming. Input from the oxygen (O
2) sensor is not
monitored during Open Loop modes. During CLOSED LOOP modes, the PCM does moni-
tor the oxygen (O
2) sensor input. The input indicates if
the calculated injector pulse width results in the ideal
air-fuel ratio for the current percentage of methanol in
the fuel. By monitoring the exhaust oxygen content
through the O
2sensor, the PCM can fine tune the
injector pulse width to achieve optimum fuel economy
combined with low emissions. The 2.5L flexible fuel multi-port fuel injection system
has the following modes of operation:
² Ignition switch ON - Zero RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
The engine start-up (crank), engine warm-up, and
wide open throttle modes are OPEN LOOP modes. The
acceleration, deceleration, and cruise modes, with the
engine at operating temperature are CLOSED
LOOP modes (under most operating conditions).
IGNITION SWITCH ON (ZERO RPM) MODE
When the ignition switch cycles and past the On
position, the fuel injection system activates and the
following actions occur:
² For two seconds at key ON (and during cranking),
the methanol concentration sensor calibrates the PCM.
During the calibration period the sensor sends 4.45
volts to the PCM as a correction factor. After the
calibration period, the methanol concentration sensor
output represents the methanol percentage in the fuel.
² The PCM calculates basic fuel strategy by determin-
ing atmospheric air pressure from the MAP sensor
input.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on this input. When the key is in the ON position and the engine is
not running, the auto shutdown (ASD) relay and fuel
pump relay are not energized. Therefore battery volt-
age is not supplied to the fuel pump, ignition coil, fuel
injector or oxygen sensor heating element.
Ä FUEL SYSTEMS 14 - 63

tween the flashes representing the first and second
digits of the code. Longer pauses separate individual
trouble codes.(3) Refer to the Diagnostic Trouble Code Charts at
the end of this group.
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 differ-
ence between a selected switch position versus an
open circuit, a short circuit, or a defective switch. If
the State Display screen shows the change from
HIGH to LOW or LOW to HIGH, assume the entire
switch circuit to the PCM functions properly. From
the state display screen, access either State Display
Inputs and Outputs or State Display Sensors.
STATE DISPLAY INPUTS AND OUTPUTS
Connect the DRBII scan tool to the vehicle and ac-
cess the State Display screen. Then access Inputs and
Outputs. The following is a list of the engine control
system functions accessible through the Inputs and
Outputs screen.
² Park/Neutral Switch (automatic transaxle only)
² Speed Control Resume
² Speed Control On/Off
² Speed Control Set
² Brake Switch
² A/C Switch Sense
² S/C Vent Solenoid
² S/C Vacuum Solenoid
² A/C Clutch Relay
² Auto Shutdown Relay
² Radiator Fan Relay
² (Duty Cycle) EVAP Purge Solenoid
² Malfunction Indicator (Check Engine) Lamp
STATE DISPLAY SENSORS
Connect the DRBII scan tool to the vehicle and ac-
cess the State Display screen. Then access Sensor
Display. The following is a list of the engine control
system functions accessible through the Sensor Dis-
play screen.
² Oxygen Sensor Signal
² Engine Coolant Temperature
² Engine Coolant Temp Sensor
² Throttle Position
² Minimum Throttle
² Battery Voltage
² MAP Sensor Reading
² Idle Air Control Motor Position
² Adaptive Fuel Factor
² Barometric Pressure
² Min Airflow Idle Spd (Speed)
² Engine Speed
² Fault #1 Key-On Info
² Module Spark Advance ²
Speed Control Target
² Fault #2 Key-on Info
² Fault #3 Key-on Info
² Speed Control Status
² Charging System Goal
² Theft Alarm Status
² Battery Temperature
² Flex Fuel (Methanol Concentration) Sensor Volt-
age
² Methanol Content (percentage)
² Map Sensor Voltage
² Vehicle Speed
² Oxygen Sensor State
² MAP Gauge Reading
² Throttle Opening (percentage)
² Total Spark Advance
CIRCUIT ACTUATION TEST MODE
The Circuit Actuation Test Mode checks for proper
operation of output circuits or devices the powertrain
control module (PCM) cannot internally recognize.
The PCM attempts to activate these outputs and al-
low 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 cor-
rectly.
OBTAINING CIRCUIT ACTUATION TEST
Connect the DRBII scan tool to the vehicle and ac-
cess the Actuators screen. The following is a list of
the engine control system functions accessible
through Actuators screens. Subordinate screens for
each actuator test are also listed. Stop All Tests
Ignition Coil No. 1
Fuel Injector No. 1
Fuel Injector No. 2
Fuel Injector No. 3
Fuel Injector No. 4
Idle Air Control Motor Open/Close
Fuel System
Radiator Fan Relay
A/C Clutch Relay
Auto Shutdown Relay
EVAP Purge Solenoid
Speed Control Servo Solenoids
Generator Field
Tachometer Output
Torque Converter Clutch Solenoid
All Solenoids/Relays
Speed Control Vent Solenoid
Speed Control Vacuum Solenoid
ASD Fuel System Test
14 - 72 FUEL SYSTEMS Ä

(1) Disconnect oxygen sensor electrical connector.
(2) Remove sensor using Tool C-4907 (Fig. 17).
Slightly tightening the sensor can ease removal. When the sensor is removed, the exhaust manifold
threads must be cleaned with an 18 mm X 1.5 + 6E tap.
If using original sensor, coat the threads with Loctite
771-64 anti-seize compound or equivalent. New sen-
sors are packaged with compound on the threads and
do not require additional compound. The sensor must
be tightened to 28 N Im (20 ft. lbs.) torque.
2.2L TURBO III MULTI-PORT FUEL INJECTIONÐSYSTEM OPERATION
INDEX
page page
Air Conditioning Clutch RelayÐPCM Output .... 89
Air Conditioning Switch SenseÐPCM Input ..... 85
Auto Shutdown (ASD) Relay and Fuel Pump RelayÐPCM Output ..................... 89
Barometric Read SolenoidÐPCM Output ....... 90
Battery VoltageÐPCM Input ................ 85
Brake SwitchÐPCM Input .................. 85
Camshaft Position SensorÐPCM Input ........ 85
Canister Purge SolenoidÐPCM Output ........ 90
CCD Bus .............................. 84
Charge Air Temperature SensorÐPCM Input . . . 86
Crankshaft Position SensorÐPCM Input ....... 87
Data Link ConnectorÐPCM Output ........... 91
Engine Coolant Temperature SensorÐPCM Input . 86
Fuel InjectorÐPCM Output ................. 91
Fuel Injectors and Fuel Rail Assembly ......... 94
Fuel Pressure Regulator ................... 94
Fuel Supply Circuit ....................... 94
General Information ....................... 83
Generator FieldÐPCM Output ............... 89 Heated Oxygen Sensor (O
2Sensor)ÐPCM Input . 88
Idle Air Control MotorÐPCM Output .......... 90
Ignition CoilÐPCM Output .................. 91
Knock SensorÐPCM Input ................. 87
Malfunction Indicator Lamp (Check Engine)ÐPCM Output ............................... 90
Manifold Absolute Pressure (Map) SensorÐPCM Input ................................ 87
Modes of Operation ....................... 92
Powertrain Control Module ................. 84
Radiator Fan RelayÐPCM Output ............ 91
Speed Control SolenoidsÐPCM Output ........ 91
Speed ControlÐPCM Input ................. 88
System Diagnosis ........................ 84
TachometerÐPCM Output .................. 91
Throttle Body ............................ 94
Throttle Position Sensor (TPS)ÐPCM Input ..... 88
Vehicle Speed SensorÐPCM Input ........... 89
Wastegate Control SolenoidÐPCM Output ..... 91
GENERAL INFORMATION
The turbocharged multi-port electronic fuel injec-
tion system combines an electronic fuel and spark
advance control system with a turbocharged intake
system (Fig. 1). The fuel injection system is con-
trolled by the powertrain control module (PCM). The PCM regulates ignition timing, air-fuel ratio,
emission control devices, cooling fan, charging sys-
tem, speed control, turbocharger wastegate and idle
speed. The PCM adapts its requirement to meet
changing operating conditions. Various sensors provide the inputs necessary for
the PCM to correctly regulate fuel flow at the fuel
injector. These include the manifold absolute pres-
sure, throttle position, oxygen sensor, coolant tem-
perature, detonation, and vehicle speed sensors. In
addition to the sensors, the air conditioning clutch
switch and various relays provide important informa-
tion and system control. The outputs include the auto
shutdown relay and fuel pump relay. All inputs to the PCM are converted into signals.
Based on these inputs the PCM adjusts air-fuel ratio,
ignition timing, turbocharger wastegate and other
Fig. 16 Heated Oxygen Sensor
Fig. 17 Oxygen Sensor Socket
Ä FUEL SYSTEMS 14 - 83

resenting throttle blade position. As the position of
the throttle blade changes, the resistance of the TPS
changes. The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The TPS
output voltage to the PCM varies from approxi-
mately 0.5 volt at minimum throttle opening (idle) to
4 volts at wide open throttle. Along with inputs from
other sensors, the PCM uses the TPS input to deter-
mine current engine operating conditions and adjust
fuel injector pulse width and ignition timing.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor (Fig. 15) is located on the
transaxle extension housing. The sensor input is
used by the PCM to determine vehicle speed and dis-
tance traveled.
The speed sensor generates 8 pulses per sensor rev-
olution. These signals, along with a closed throttle
signal from the TPS, determine if a closed throttle
deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain desired
engine speed.
AIR CONDITIONING CLUTCH RELAYÐPCM
OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit. The radiator fan relay supplies bat-
tery power to the solenoid side of the A/C clutch re-
lay. The air conditioning clutch relay will not
energize unless the radiator fan relay energizes. The
PCM energizes the radiator fan relay when the air
conditioning or defrost switch is put in the ON posi-
tion and the low pressure and high pressure switches
close. When the PCM senses wide open throttle
through the throttle position sensor, or low engine
RPM it will de-energize the A/C clutch relay, open
it's contacts and prevent air conditioning clutch en-
gagement. On AG Body vehicles, the relay is located in the
power distribution center (Fig. 16).
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.
AUTO SHUTDOWN (ASD) RELAY AND FUEL PUMP
RELAYÐPCM OUTPUT
The PCM operates the auto shutdown (ASD) relay
and fuel pump relay through one ground path. The
PCM operates the relays by switching the ground
path on and off. Both relays turn on and off at the
same time. The ASD relay connects battery voltage to the fuel
injector and ignition coil. The fuel pump relay con-
nects battery voltage to the fuel pump and oxygen
sensor heating element. The PCM turns the ground path off when the igni-
tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank po-
Fig. 14 Throttle Position Sensor and Idle Air Control Motor
Fig. 15 Vehicle Speed Sensor
Fig. 16 Power Distribution CenterÐAG Body
Ä FUEL SYSTEMS 14 - 89

sition, the PCM monitors the crankshaft position and
camshaft position sensor signals to determine engine
speed and ignition timing (coil dwell). If the PCM
does not receive the crankshaft position sensor and
camshaft position sensor signals when the ignition
switch is in the Run position, it de-energizes both re-
lays. When the relays are de-energized, battery volt-
age is not supplied to the fuel injector, ignition coil,
fuel pump and oxygen sensor heating element. The ASD relay and fuel pump relay are located in
the power distribution center (Fig. 16).
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The idle air control motor is mounted on the throt-
tle body (Fig. 14). The PCM operates the motor. The
PCM adjusts engine idle speed through the idle air
control motor to compensate for engine load or ambi-
ent conditions. The throttle body has an air bypass passage that
provides air for the engine at idle (the throttle blade
is closed). The idle air control motor pintle protrudes
into the air bypass passage and regulates air flow
through it. The PCM adjusts engine idle speed by moving the
idle air control motor pintle in and out of the bypass
passage. The adjustments are based on inputs the
PCM receives. The inputs are from the throttle posi-
tion sensor, camshaft position sensor, crankshaft po-
sition sensor, coolant temperature sensor, and
various switch operations (brake and air condition-
ing). Deceleration die out is also prevented by in-
creasing airflow when the throttle is closed quickly
after a driving (speed) condition.
BAROMETRIC READ SOLENOIDÐPCM OUTPUT
The barometric pressure read solenoid is spliced
into the manifold absolute pressure (MAP) sensor
vacuum hose (Fig. 12). The barometric read solenoid
switches the pressure supply to the MAP sensor from
either barometric pressure (atmospheric) or manifold
vacuum. The PCM operates the solenoid. Atmospheric pressure is periodically supplied to
the MAP sensor to measure barometric pressure.
This occurs at closed throttle, once per throttle clo-
sure but no more often than once every 3 minutes
and within a specified RPM band. Barometric infor-
mation is used primarily for boost control and start
fuel enrichment at various altitudes.
CANISTER PURGE SOLENOIDÐPCM OUTPUT
Vacuum for the Evaporative Canister is controlled
by the Canister Purge Solenoid (Fig. 17). The sole-
noid is controlled by the PCM. The PCM operates the solenoid by switching the
ground circuit on and off. When grounded, the sole-
noid energizes and prevents vacuum from reaching
the evaporative canister. When not energized the so-
lenoid allows vacuum to flow to the canister. During warm-up and for a specified time period after
hot starts the PCM grounds the purge solenoid.
Vacuum does not operate the evaporative canister
valve. The PCM removes the ground to the solenoid when
the engine reaches a specified temperature and the
time delay interval has occurred. When the solenoid is
de-energized, vacuum flows to the canister purge
valve. Vapors are purged from the canister and flow to
the throttle body. The purge solenoid will also be energized during
certain idle conditions, in order to update the fuel
delivery calibration.
MALFUNCTION INDICATOR LAMP (CHECK
ENGINE)ÐPCM OUTPUT
The malfunction indicator lamp (instrument panel
Check Engine lamp) comes on each time the ignition
key is turned ON and stays on for 3 seconds as a bulb
test. The malfunction indicator lamp warns the opera-
tor that the PCM has entered a Limp-in mode. During
Limp-in-Mode, the PCM attempts to keep the system
operational. The malfunction indicator lamp signals
the need for immediate service. In limp-in mode, the
PCM compensates for the failure of certain components
that send incorrect signals. The PCM substitutes for
the incorrect signals with inputs from other sensors. Signals that can trigger the malfunction indi-
cator lamp (Check Engine Lamp).
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Throttle Position Sensor
² Battery Voltage Input
² An Emissions Related System
² Charging system
The malfunction indicator lamp can also be used to
display diagnostic trouble codes. Cycle the ignition
switch on, off, on, off, on, within five seconds and any
Fig. 17 EVAP Canister Purge Solenoid and Waste- gate Control Solenoid
14 - 90 FUEL SYSTEMS Ä

SYSTEM TESTS
Apply parking brake and/or block wheels be-
fore performing idle check or adjustment, or any
engine running tests.
OBTAINING DIAGNOSTIC TROUBLE CODES
(1) Connect DRBII scan tool to the data link connec-
tor (Fig. 1). (2) Start the engine if possible, cycle the trans mis-
sion selector and the A/Cswitch if applicable. Shut off
the engine. (3) Turn the ignition switch on, access Read Fault
Screen. Record all the fault messages shown on the
DRBII scan tool. Observe the malfunction indicator
lamp (check engine lamp on the instrument panel). The
lamp should light for 2 seconds then go out (bulb
check). Diagnostic trouble code erasure: access erase
diagnostic trouble code data.
STATE DISPLAY TEST MODE
The switch inputs used by the powertrain control
module (PCM) have only two recognized states, HIGH
and LOW. For this reason, the PCM cannot recognize
the difference between a selected switch position ver-
sus an open circuit, a short circuit, or a defective
switch. If the display changes, assume the entire
switch circuit to the PCM is functional. From the state
display screen access either State Display Inputs and
Outputs or State Display Sensors.
STATE DISPLAY INPUTS AND OUTPUTS
Connect the DRBII scan tool to the vehicle and access
the State Display screen. Then access Inputs and
Outputs. The following is a list of the engine control
system functions accessible through the Inputs and
Outputs screen. Speed Control Resume
Brake Switch
Speed Control On/Off
Speed Control Set
A/C Switch Sense
S/C Vent Solenoid S/C Vacuum Solenoid
A/C Clutch Relay
Baro Read Solenoid
Wastegate Solenoid
Auto Shutdown Relay
Radiator Fan Relay
Purge Solenoid
Malfunction Indicator Lamp (Check Engine Lamp)
STATE DISPLAY SENSORS
Connect the DRBII scan tool to the vehicle and ac-
cess the State Display screen. Then access Sensor
Display. The following is a list of the engine control
system functions accessible through the Sensor Dis-
play screen. Oxygen Sensor Signal
Coolant Temperature
Coolant Temp Sensor
Throttle Position
Minimum Throttle
Knock Sensor Signal
Battery Voltage
MAP Sensor Reading
Idle Air Control Motor Position
Adaptive Fuel Factor
Barometric Pressure
Min Airflow Idle Spd (speed)
Engine Speed
DIS Sensor Status
Fault #1 Key-On Info
Module Spark Advance
Cyl 1 Knock Retard
Cyl 2 Knock Retard
Cyl 3 Knock Retard
Cyl 4 Knock Retard
Boost Pressure Goal
Charge Temperature
Charge Temp Sensor
Speed Control Target
Fault #2 Key-on Info
Fault #3 Key-on Info
Speed Control Status
Charging System Goal
Theft Alarm Status
DIAGNOSTIC TROUBLE CODE DESCRIPTION (CON'T)
14 - 104 FUEL SYSTEMS Ä

3.0L MULTI-PORT FUEL INJECTIONÐSYSTEM OPERATION INDEX
page page
Air Conditioning (A/C) Clutch Relay (AA, AG, AJ Body)ÐPCM Output .................... 118
Air Conditioning (A/C) Clutch Relay (AC Body) ÐPCM Output ........................ 118
Air Conditioning Switch Sense (AA, AG, AJ Body)ÐPCM Input ..................... 115
Air Conditioning Switch Sense (AC Body)ÐPCM Input ................................ 115
Auto Shutdown (ASD) Relay and Fuel Pump RelayÐPCM Output .................... 119
Battery VoltageÐPCM Input ............... 115
Brake SwitchÐPCM Input ................. 115
CCD Bus .............................. 113
Data Link ConnectorÐPCM Output .......... 120
Distributor Pick-UpÐPCM Input ............. 115
Duty Cycle Evap Canister Purge Solenoid ÐPCM Output ........................ 119
Engine Coolant Temperature Sensor ÐPCM Input ......................... 115
Fuel InjectorsÐPCM Output ............... 120
Fuel Pressure Regulator .................. 124
Fuel Supply Circuit ...................... 123
General Information ...................... 113 Generator FieldÐPCM Output
.............. 118
Heated Oxygen Sensor (O
2Sensor)
ÐPCM Input ......................... 116
Idle Air Control MotorÐPCM Output ......... 119
Ignition CoilÐPCM Output ................. 121
Malfunction Indicator Lamp (Check Engine Lamp)ÐPCM Output ................... 120
Manifold Absolute Pressure (MAP) Sensor ÐPCM Input ......................... 116
Modes of Operation ...................... 121
Park/Neutral SwitchÐPCM Input ............ 117
Part Throttle Unlock SolenoidÐPCM Output . . . 121
Powertrain Control Module ................. 113
Radiator Fan RelayÐPCM Output ........... 121
Speed Control SolenoidsÐPCM Output ....... 121
Speed ControlÐPCM Input ................ 117
System Diagnosis ....................... 113
TachometerÐPCM Output ................. 121
Throttle Body ........................... 123
Throttle Position Sensor (TPS)ÐPCM Input .... 117
Transaxle Control ModuleÐPCM Output ...... 120
Vehicle Speed and Distance InputÐPCM Input . 118
Vehicle Speed SensorÐPCM Input .......... 118
GENERAL INFORMATION
The 3.0L engine uses a sequential Multi-Port Elec-
tronic Fuel Injection system (Fig. 1). The MPI system
is computer regulated and provides precise air/fuel
ratios for all driving conditions. The MPI system is operated by the powertrain con-
trol module (PCM). The PCM regulates ignition timing, air-fuel ratio,
emission control devices, cooling fan, charging sys-
tem, idle speed and speed control. Various sensors
provide the inputs necessary for the PCM to correctly
operate these systems. In addition to the sensors,
various switches also provide inputs to the PCM. All inputs to the PCM are converted into signals.
The PCM can adapt its programming to meet chang-
ing operating conditions. Fuel is injected into the intake port above the in-
take valve in precise metered amounts through elec-
trically operated injectors. The PCM fires the
injectors in a specific sequence. The PCM maintains
an air fuel ratio of 14.7 parts air to 1 part fuel by
constantly adjusting injector pulse width. Injector
pulse width is the length of time the injector is ener-
gized. The PCM adjusts injector pulse width by opening
and closing the ground path to the injector. Engine
RPM (speed) and manifold absolute pressure (air
density) are the primary inputs that determine injec-
tor pulse width.
SYSTEM DIAGNOSIS
The powertrain control module (PCM) tests many
of its own input and output circuits. If a fault is
found in a major system, the information is stored in
memory. Technicians can display fault information
through the malfunction indicator lamp (instrument
panel Check Engine lamp) or by connecting the
DRBII scan tool. For diagnostic trouble code informa-
tion, refer to the 3.0 Multi-Port Fuel InjectionÐOn-
Board Diagnostics section of this group.
CCD BUS
Various modules exchange information through a
communications port called the CCD Bus. The pow-
ertrain control module (PCM) transmits the malfunc-
tion indicator (instrument panel check engine lamp)
On/Off signal, engine RPM and vehicle load data on
the CCD Bus.
POWERTRAIN CONTROL MODULE
The powertrain control module (PCM) is a digital
computer containing a microprocessor (Fig. 2). The
PCM receives input signals from various switches
and sensors that are referred to as PCM Inputs.
Based on these inputs, the PCM adjusts various en-
gine and vehicle operations through devices referred
to as PCM Outputs. PCM Inputs:
² Air Conditioning Controls
² Battery Voltage
² Brake Switch
Ä FUEL SYSTEMS 14 - 113

VEHICLE SPEED AND DISTANCE INPUTÐPCM
INPUT
On vehicles equipped with an electronic transaxle
(41TE), the transaxle output speed sensor supplies
the vehicle speed and distance inputs to the PCM.
The output speed sensor is located on the side of the
transaxle (Fig. 9). The speed and distance signals, along with a closed
throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.
VEHICLE SPEED SENSORÐPCM INPUT
Vehicles with 3 speed automatic transaxles or
manual transaxles use vehicle speed sensors. On
both transaxles, the vehicle speed sensor (Fig. 11) is
located on the extension housing. The sensor input is
used by the PCM to determine vehicle speed and dis-
tance traveled.
The vehicle speed sensor generates 8 pulses per
sensor revolution. These signals, along with a closed
throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.
AIR CONDITIONING (A/C) CLUTCH RELAY (AC
BODY)ÐPCM OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit. The ignition switch supplies battery
power to the solenoid side of the relay. The A/C fan
relay is operated independently of the PCM by the Fan Cutout switch. When the A/C clutch relay ener-
gizes, battery voltage powers the A/C compressor
clutch.
With the engine operating and the blower motor
switch in the On position, the PCM turns the A/C
clutch on when the A/C switch closes. When the
PCM senses low idle speeds or wide open throttle
through the throttle position sensor, it de-energizes
the A/C clutch relay. The relay contacts open, pre-
venting air conditioning clutch engagement. On AC body vehicles, the relay is located in the
power distribution center (Fig. 12).
AIR CONDITIONING (A/C) CLUTCH RELAY (AA, AG,
AJ BODY)ÐPCM OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit. The ignition switch supplies battery
power to the solenoid side of the relay. When the A/C
clutch relay energizes, battery voltage powers the
A/C compressor clutch. With the engine operating and the blower motor
switch in the On position, the PCM cycles the air
conditioning clutch on and off when the A/C switch
closes. When the PCM senses low idle speeds or wide
open throttle through the throttle position sensor, it
de-energizes the A/C clutch relay. The relay contacts
open, preventing air conditioning clutch engagement. On AA body vehicles, the relay is located next to
the drivers side strut tower (Fig. 13). On AG and AJ body vehicles, the relay is located
in the power distribution center (Fig. 14).
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.
Fig. 11 Vehicle Speed SensorÐTypical
Fig. 12 Relay Identification (AC Body)
14 - 118 FUEL SYSTEMS Ä

MALFUNCTION INDICATOR LAMP (CHECK ENGINE
LAMP)ÐPCM OUTPUT
The malfunction indicator lamp (instrument panel
Check Engine lamp) comes on each time the ignition
key is turned ON and stays on for 3 seconds as a bulb
test. The malfunction indicator lamp warns the opera-
tor that the PCM has entered a Limp-in mode. During
Limp-in Mode, the PCM attempts to keep the system
operational. The malfunction indicator lamp signals
the need for immediate service. In limp-in mode, the
PCM compensates for the failure of certain components
that send incorrect signals. The PCM substitutes for
the incorrect signals with inputs from other sensors. Signals that can trigger the malfunction indi-
cator lamp (Check Engine Lamp).
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Throttle Position Sensor
² Battery Voltage Input
² An Emission Related System (California vehicles)
² Charging system
The malfunction indicator lamp displays diagnostic
trouble codes. Cycle the ignition switch on, off, on, off,
on, within five seconds to display any diagnostic
trouble codes stored in the PCM. Refer to the 3.0L
Multi-Port Fuel InjectionÐOn-Board Diagnostics sec-
tion of this Group for Diagnostic trouble code Descrip-
tions.
DATA LINK CONNECTORÐPCM OUTPUT
The data link connector provides the technician with
the means to connect the DRBII scan tool to diagnosis
the vehicle.
TRANSAXLE CONTROL MODULEÐPCM OUTPUT
The PCM supplies the following information to the
electronic automatic transaxle control module through
the CCD Bus:
² battery temperature ²
brake switch input
² engine coolant temperature
² manifold absolute pressure (MAP)
² speed control information
FUEL INJECTORSÐPCM OUTPUT
The fuel injectors are electrical solenoids (Fig. 16).
The injector contains a pintle that closes off an ori-
fice at the nozzle end. When electric current is sup-
plied to the injector, the armature and pintle move a
short distance against a spring, allowing fuel to flow
out the orifice. Because the fuel is under high pres-
sure, a fine spray is developed in the shape of a hol-
low cone. The spraying action atomizes the fuel,
adding it to the air entering the combustion cham-
ber.
The injectors are positioned in the intake manifold
with the nozzle ends directly above the intake valve
port (Fig. 16).
The fuel injectors are operated by the PCM. They
are energized in a sequential order during all engine
operating conditions except start up. The PCM ini-
Fig. 16 Fuel InjectorÐ3.0L Engine
Fig. 17 Fuel Injector Location
Fig. 15 EVAP Purge Solenoid
14 - 120 FUEL SYSTEMS Ä

SYSTEM TESTS
WARNING: APPLY PARKING BRAKE AND/OR BLOCK
WHEELS BEFORE PERFORMING ANY TEST ON AN
OPERATING ENGINE.
OBTAINING DIAGNOSTIC TROUBLE CODES
(1) Connect DRBII scan tool to the data link connec-
tor located in the engine compartment near the pow-
ertrain control module (PCM). (2) Start the engine if possible, cycle the transaxle
selector and the A/Cswitch if applicable. Shut off the
engine. (3) Turn the ignition switch on, access Read Fault
Screen. Record all the fault messages shown on the
DRBII scan tool. Observe the malfunction indicator
lamp (Check Engine lamp on the instrument panel).
The lamp should light for 3 seconds then go out (bulb
check). Diagnostic trouble code erasure; access erase
diagnostic trouble code data
STATE DISPLAY TEST MODE
The switch inputs used by the powertrain control
module (PCM) have only two recognized states, HIGH
and LOW. For this reason, the PCM cannot recognize
the difference between a selected switch position ver-
sus an open circuit, a short circuit, or a defective
switch. If the change is displayed, it can be assumed
that the entire switch circuit to the PCM is functional.
From the state display screen access either State
Display Inputs and Outputs or State Display Sensors.
STATE DISPLAY INPUTS AND OUTPUTS
Connect the DRBII scan tool to the vehicle. Access
the State Display screen. Then access Inputs and
Outputs. The following is a list of the engine control
system functions accessible through the Inputs and
Outputs screen. Park/Neutral Switch
Speed Control Resume
Brake Switch
Speed Control On/Off
Speed Control Set
A/C Switch Sense
S/C Vent Solenoid
S/C Vacuum Solenoid
A/C Clutch Relay
EGR Solenoid
Auto Shutdown Relay
Radiator Fan Relay
Purge Solenoid
Torque Converter Clutch Solenoid
Malfunction Indicator Lamp (Check Engine Lamp)
STATE DISPLAY SENSORS
Connect the DRBII scan tool to the vehicle and ac-
cess the State Display screen. Then access Sensor
Display. The following is a list of the engine control
system functions accessible through the Sensor Dis-
play screen. Battery Temperature
Oxygen Sensor Signal
Engine Coolant Temperature
Engine Coolant Temp Sensor
Throttle Position
Minimum Throttle
Battery Voltage
MAP Sensor Reading
Idle Air Control Motor Position
Adaptive Fuel Factor
Barometric Pressure
Min Airflow Idle Speed
Engine Speed
Fault #1 Key-On Info
Module Spark Advance
Speed Control Target
Fault #2 Key-on Info
Fault #3 Key-on Info
Speed Control Status
Speed Control Switch Voltage
Charging System Goal
Theft Alarm Status
Map Sensor Voltage
Vehicle Speed
Oxygen Sensor State
MAP Gauge Reading
Throttle Opening (percentage)
Total Spark Advance
CIRCUIT ACTUATION TEST MODE
The circuit actuation test mode checks for proper
operation of output circuits or devices which the pow-
ertrain control module (PCM) cannot internally rec-
ognize. The PCM can attempt to activate these
outputs and allow an observer to verify proper oper-
ation. Most of the tests provide an audible or visual
indication of device operation (click of relay contacts,
spray fuel, etc.). Except for intermittent conditions, if
a device functions properly during testing, assume
the device, its associated wiring, and driver circuit
working correctly.
OBTAINING CIRCUIT ACTUATION TEST
Connect the DRBII scan tool to the vehicle and ac-
cess the Actuators screen. The following is a list of
the engine control system functions accessible
through Actuators screens. Stop All Tests
Ignition Coil #1
Fuel Injector #1
Fuel Injector #2
Fuel Injector #3
14 - 134 FUEL SYSTEMS Ä