key CHEVROLET DYNASTY 1993 Owners 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

2.5L FLEXIBLE FUEL MULTI-PORT FUEL INJECTIONÐON-BOARD DIAGNOSTICS INDEX
page page
Circuit Actuation Test Mode ................. 72
Diagnostic Trouble Codes ................... 71
General Information ....................... 70
High and Low Limits ....................... 71
Ignition Timing Procedure ................... 73 Monitored Circuits
........................ 70
Non-Monitored Circuits ..................... 70
Powertrain Control Module 60-Way Connector . . . 73
State Display Test Mode .................... 72
Throttle Body Minimum Air Flow Check Procedure.. 73
GENERAL INFORMATION
The powertrain control module (PCM) monitors
many different circuits in the fuel injection system. If
the PCM senses a problem with a monitored circuit
often enough to indicate an actual problem, it stores a
diagnostic trouble code in the PCM's memory. If the
problem is repaired or ceases to exist, the PCM cancels
the diagnostic trouble code after 51 vehicle key on/off
cycles. Certain criteria must be met before the PCM stores a
diagnostic trouble code in memory. The criteria may be
a specific range of engine RPM, engine temperature,
and/or input voltage to the PCM. The PCM might not store a diagnostic trouble code
for a monitored circuit even though a malfunction has
occurred. This may happen because one of the diagnos-
tic trouble code criteria for the circuit has not been met.
For example , assume the diagnostic trouble code
criteria for a certain sensor requires the PCM to
monitor the circuit only when the engine operates
between 750 and 2000 RPM. Suppose the sensor's
output circuit shorts to ground when engine operates
above 2400 RPM (resulting in 0 volt input to the PCM).
Because the condition happens at an engine speed
above the maximum threshold (2000 rpm), the PCM
will not store a diagnostic trouble code. There are several operating conditions for which the
PCM monitors and sets diagnostic trouble codes. Refer
to Monitored Circuits and Non-Monitored Circuits in
this section. Technicians can display stored diagnostic trouble
codes by two different methods. The first is to cycle the
ignition switch On - Off - On - Off - On within 5
seconds. Then count the number of times the malfunc-
tion indicator lamp (check engine lamp) on the instru-
ment panel flashes on and off. The number of flashes
represents the trouble code. There is a slight pause
between the flashes representing the first and second
digits of the code. Longer pauses separate individual
trouble codes. The second method of reading diagnostic trouble
codes uses the DRBII scan tool. The DRBII scan tool
connects to the data link (diagnostic) connector in the vehicle (Fig. 1). For diagnostic trouble code informa-
tion, refer to charts in this section.
MONITORED CIRCUITS
The PCM can detect certain fault conditions in the
fuel injection system. Open or Shorted Circuit - The PCM can determine
if the sensor output (input to the PCM) is within proper
range. Also, the PCM can determine open or shorted
circuits. Output Device Current Flow - The PCM senses
whether output devices are hooked up. If a problem
exists within the circuit, the PCM senses whether the
circuit is open, shorted to ground, or shorted high. Heated Oxygen Sensor - Once the system has
entered closed loop, the PCM determines if the oxygen
sensor is switching between rich and lean. Refer to
Modes of Operation in the General Information section
of this group for an explanation of closed loop opera-
tion.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems and conditions that could have malfunctions
causing driveability problems. The PCM might not
store diagnostic trouble codes for these conditions.
However, problems with these systems may cause
Fig. 1 Data Link (Diagnostic) Connector
14 - 70 FUEL SYSTEMS Ä

the PCM to store diagnostic trouble codes for other
systems. For example, a fuel pressure problem will not
register a fault directly, but could cause a rich or lean
condition. This could cause the PCM to store an oxygen
sensor diagnostic trouble code. Fuel Pressure - The vacuum assisted fuel pressure
regulator controls fuel system pressure. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, stuck open regulator, or a pinched
fuel supply or return line. However, these could result
in a rich or lean condition causing the PCM to store an
oxygen sensor diagnostic trouble code. Secondary Ignition Circuit - The PCM cannot
detect an inoperative ignition coil, fouled or worn spark
plugs, ignition cross firing, or open spark plug cables. Engine Timing - The PCM cannot detect an incor-
rectly indexed timing belt, camshaft sprocket and
crankshaft sprocket. However, these could result in a
rich or lean condition causing the PCM to store an
oxygen sensor diagnostic trouble code. Cylinder Compression - The PCM cannot detect
uneven, low, or high engine cylinder compression. Exhaust System - The PCM cannot detect a
plugged, restricted or leaking exhaust system. Fuel Injector Mechanical Malfunctions - The
PCM cannot determine if a fuel injector is clogged, the
needle is sticking or if the wrong injector is installed.
However, these could result in a rich or lean condition
causing the PCM to store an oxygen sensor diagnostic
trouble code. Excessive Oil Consumption - Although the PCM
monitors exhaust stream oxygen content when the
system is in closed loop, it cannot determine excessive
oil consumption. Throttle Body Air Flow - The PCM cannot detect a
clogged or restricted air cleaner inlet or filter element. Evaporative System - The PCM cannot detect a
disconnected (open vacuum line) restricted, plugged or
loaded evaporative purge canister. Vacuum Assist - The PCM cannot detect leaks or
restrictions in the vacuum circuits of vacuum assisted
engine control system devices. However, these could
cause the PCM to store a MAP sensor diagnostic
trouble code and cause a high idle condition. PCM System Ground - The PCM cannot determine
a poor system ground. However, one or more diagnostic
trouble codes may be generated as a result of this
condition. PCM Connector Engagement - The PCM may not
be able to determine spread or damaged connector
pins. However, it might store diagnostic trouble codes
as a result of spread connector pins.HIGH AND LOW LIMITS
The PCM compares input signal voltages from each
input device with established high and low limits for the
device. If the input voltage is not within limits and other
criteria are met, the PCM stores a diagnostic trouble code
in memory. Other diagnostic trouble code criteria might
include engine RPM limits or input voltages from other
sensors or switches that must be present before verifying
a diagnostic trouble code condition.
DIAGNOSTIC TROUBLE CODES
A diagnostic trouble code indicates the powertrain
control module (PCM) has recognized an abnormal
condition in the system. Abnormal conditions are usu-
ally shorted or open circuits.
The technician can display diagnostic trouble codes in
two ways. The first way is to cycle the ignition switch and
count the number of times the malfunction indicator lamp
(check engine lamp on the instrument panel) flashes on
and off. The DRBII scan tool provides the second method
of displaying diagnostic trouble codes. Diagnostic trouble
codes indicate the results of a circuit failure, but do not
directly identify the failed component.
For a list of Diagnostic Trouble Codes, refer to
the charts at the end of this section.
OBTAINING DIAGNOSTIC TROUBLE CODES
USING DRBII SCAN TOOL
WARNING: APPLY PARKING BRAKE AND/OR BLOCK
WHEELS BEFORE PERFORMING ANY TEST ON AN
OPERATING ENGINE. (1) Connect DRBII scan tool to the data link (diag-
nostic) connector located in the engine compartment,
next to the PCM (Fig. 1). (2) If possible, start the engine and cycle the A/C
switch if applicable. Shut off the engine. (3)
Turn the ignition switch on, access Read Fault
Screen. Record all the diagnostic trouble codes 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)].
To erase diagnostic trouble codes, use the Erase
Trouble Code data screen on the DRBII scan tool.
USING THE MALFUNCTION INDICATOR LAMP (1) Cycle the ignition key On - Off - On - Off - On
within 5 seconds. (2) Count the number of times the malfunction indi-
cator lamp (check engine lamp on the instrument
panel) flashes on and off. The number of flashes
represents the trouble code. There is a slight pause be-
Ä FUEL SYSTEMS 14 - 71

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

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

noid is energized. The solenoid mounts to the passen-
ger side inner fender panel, next to the strut tower
(Fig. 17).
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. This input indicates
to the PCM whether or not the calculated injector pulse
width results in the ideal air-fuel ratio of 14.7 parts air
to 1 part 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 2.2L Turbo III 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 activates the fuel injection
system the following actions occur:
²
The PCM calculates basic fuel strategy by determining
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.
ENGINE START-UP MODE
This is an OPEN LOOP mode. The following actions
occur when the starter motor is engaged. If the PCM receives the camshaft position and crank-
shaft position sensor signals, it energizes the auto
shutdown (ASD) relay and fuel pump relay. These
relays supply battery voltage to the fuel pump, fuel
injectors, ignition coil, and oxygen sensor heating ele-
ment. If the PCM does not receive the camshaft posi-
tion sensor and crankshaft position sensor signals
within approximately one second, it de-energizes the
ASD relay and fuel pump relay. The PCM energizes all injectors until it determines
crankshaft position from the camshaft position sensor
and crankshaft position sensor signals. The PCM de-
termines crankshaft position within 1 engine revolu-
tion. After determining crankshaft position, the PCM be-
gins energizing the injectors in sequence. The PCM
adjusts injector pulse width and controls injector syn-
chronization by turning the individual ground paths to
the injectors On and Off. When the engine idles within 664 RPM of its target
RPM, the PCM compares current MAP sensor value
with the atmospheric pressure value received during
the Ignition Switch On (zero RPM) mode. If the PCM
does not detect a minimum difference between the two
values, it sets a MAP fault into memory. Once the ASD and fuel pump relays have been
energized, the PCM:
² Determines injector pulse width based on coolant
temperature, manifold absolute pressure (MAP) and
the number of engine revolutions since cranking was
initiated.
² Monitors the coolant temperature sensor, camshaft
position sensor, crankshaft position sensor, MAP sen-
sor, and throttle position sensor to determine correct
ignition timing.
ENGINE WARM-UP MODE
This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure (MAP)
² engine speed (crankshaft position sensor)
² throttle position
² A/C switch
² battery voltage
The PCM provides a ground path for the injectors to
precisely control injector pulse width (by switching the
ground on and off). The PCM adjusts engine idle speed
through the idle air control motor. Also, the PCM
regulates ignition timing.
14 - 92 FUEL SYSTEMS Ä

2.2L TURBO III MULTI-PORT FUEL INJECTIONÐON-BOARD DIAGNOSTICS INDEX
page page
60-Way PCM Wiring Connector ............. 105
Circuit Actuation Test Mode ................ 105
Diagnostic Trouble Code Description ......... 101
General Information ...................... 100
High and Low Limits ..................... 101
Ignition Timing Procedure ................. 105 Monitored Circuits
....................... 100
Non-Monitored Circuits ................... 100
State Display Test Mode .................. 104
System Tests .......................... 104
Throttle Body Minimum Air Flow Check Procedure ............................ 105
GENERAL INFORMATION
The powertrain control module (PCM) has been pro-
grammed to monitor many different circuits of the fuel
injection system. If a problem is sensed with a moni-
tored circuit often enough to indicate an actual prob-
lem, the PCM stores a fault. If the problem is repaired
or ceases to exist, the PCM cancels the Diagnostic
trouble code after 51 vehicle key on/off cycles. Certain criteria must be met for a diagnostic trouble
code to be entered into PCM memory. The criteria may
be a specific range of engine RPM, engine temperature,
and/or input voltage to the PCM. It is possible that a diagnostic trouble code for a
monitored circuit may not be entered into memory
even though a malfunction has occurred. This may
happen because one of the diagnostic trouble code
criteria for the circuit has not been met. For example,
assume that one of the diagnostic trouble code criteria
for a certain sensor circuit is that the engine must be
operating between 750 and 2000 RPM. If the sensor
output circuit shorts to ground when engine RPM is
above 2400 RPM (resulting i n a 0 volt input to the
PCM) a diagnostic trouble code will not be entered into
memory. This is because the condition does not occur
within the specified RPM range. There are several operating conditions for which the
PCM does not monitor and set diagnostic trouble codes.
Refer to Monitored Circuits and Non-Monitored Cir-
cuits in this section. Stored diagnostic trouble codes can be displayed
either by cycling the ignition key On - Off - On - Off -
On, or through use of the DRB II scan tool. The DRBII
scan tool connects to the data link connector in the
vehicle (Fig. 1).
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain fault conditions in the fuel injection system. Open or Shorted Circuit - The PCM can determine
if the sensor output (input to PCM) is within proper
range. Also, the PCM can determine if the circuit is
open or shorted. Output Device Current Flow - The PCM senses
whether the output devices are hooked up. If there is a problem with the circuit, the PCM senses whether
the circuit is open, shorted to ground, or shorted
high. Oxygen Sensor - The PCM can determine if the
oxygen sensor is switching between rich and lean
once the system has entered closed loop. Refer to
Modes of Operation in this section for an explanation
of closed loop operation.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems and conditions that could have malfunctions
that result in driveability problems. Diagnostic trou-
ble codes may not be displayed for these conditions.
However, problems with these systems may cause di-
agnostic trouble codes to be displayed for other sys-
tems. For example, a fuel pressure problem will not
register a fault directly, but could cause a rich or
lean condition. This could cause an oxygen sensor
fault to be stored in the PCM. Fuel Pressure - Fuel pressure is controlled by the
fuel pressure regulator. The PCM cannot detect a
clogged fuel pump inlet strainer, clogged in-line fuel
filter, or a pinched fuel supply or return line. How-
ever, these could result in a rich or lean condition
causing an oxygen sensor fault to be stored in the
PCM.
Fig. 1 Data Link Connector LocationÐAG Body
14 - 100 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

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

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 multi-port fuel injection system is acti-
vated by the ignition switch, the following actions
occur:
² The PCM determines atmospheric air pressure from
the MAP sensor input to determine basic fuel strategy.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on these inputs. When the key is in the ON position and the engine is
not running (zero rpm), the auto shutdown (ASD) relay
and fuel pump relay are not energized. Therefore
battery voltage is not supplied to the fuel pump,
ignition coil, fuel injectors or oxygen sensor heating
element.
ENGINE START-UP MODE
This is an OPEN LOOP mode. The following actions
occur when the starter motor is engaged. If the PCM receives a distributor signal, it energizes
the auto shutdown (ASD) relay and fuel pump relay.
These relays supply battery voltage to the fuel pump,
fuel injectors, ignition coil, and oxygen sensor heating
element. If the PCM does not receive a distributor
input, the ASD relay and fuel pump relay will be
de-energized after approximately one second. The PCM energizes all six injectors until it deter-
mines crankshaft position from the distributor pick-up
signals. The PCM determines crankshaft position
within 2 engine revolutions. After determining crankshaft position, the PCM be-
gins energizing the injectors in sequence. The PCM
adjusts injector pulse width and controls injector syn-
chronization by turning the individual ground paths to
the injectors On and Off. When the engine idles within 664 RPM of its target
RPM, the PCM compares current MAP sensor value
with the atmospheric pressure value received during
the Ignition Switch On (zero RPM) mode. If the PCM
does not detect a minimum difference between the two
values, it sets a MAP fault into memory. Once the ASD and fuel pump relays have been
energized, the PCM:
² determines injector pulse width based on coolant
temperature, manifold absolute pressure (MAP) and
the number of engine revolutions since cranking was
initiated. ²
monitors the coolant temperature sensor, distribu-
tor pick-up, MAP sensor, and throttle position sensor
to determine correct ignition timing.
ENGINE WARM-UP MODE
This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² engine coolant temperature
² crankshaft position (distributor pick-up)
² manifold absolute pressure (MAP)
² engine speed (distributor pick-up)
² throttle position
² A/C switch
² battery voltage
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off. The PCM adjusts engine idle speed by regulating
the idle air control motor and ignition timing.
CRUISE OR IDLE MODE
When the engine is at operating temperature this
is a CLOSED LOOP mode. During cruising speed the
following inputs are received by the PCM:
² engine coolant temperature
² crankshaft position (distributor pick-up)
² manifold absolute pressure
² engine speed (distributor pick-up)
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off. The PCM adjusts engine idle speed and ignition
timing. The PCM controls the air/fuel ratio according
to the oxygen content in the exhaust gas.
ACCELERATION MODE This is a CLOSED LOOP mode. The PCM recog-
nizes an abrupt increase in throttle position or MAP
pressure as a demand for increased engine output
and vehicle acceleration. The PCM increases injector
pulse width in response to increased fuel demand.
DECELERATION MODE This is a CLOSED LOOP mode. During decelera-
tion the following inputs are received by the PCM:
² engine coolant temperature
² crankshaft position (distributor pick-up)
² manifold absolute pressure
² engine speed (distributor pick-up)
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
14 - 122 FUEL SYSTEMS Ä