3.2.3 OTHER CONTROLS
CHARGING SYSTEM
The charging system is turned on when the
engine is started and ASD relay energized. When
the ASD relay is on, ASD output voltage is supplied
to the ASD sense circuit at the PCM. This voltage is
connected in some cases, through the PCM and
supplied to one of the generator field terminals
(Gen Source +). All others, the Gen field is con-
nected directly to the ASD output voltage. The
amount of current produced by the generator is
controlled by the Electronic Voltage Regulator
(EVR) circuitry, in the PCM. A battery temperature
sensor, located either in the battery tray, using the
ambient sensor, or in the PCM itself, is used to
sense battery temperature. This temperature along
with sensed line voltage, is used by the PCM to vary
the battery charging rate. This is done by cycling
the ground path to the other generator field termi-
nal (Gen field driver).
SPEED CONTROL SYSTEM
The PCM controls vehicle speed by operation of
the speed control servo vacuum and vent solenoids.
Energizing the vacuum solenoid applies vacuum to
the servo to increase throttle position. Operation of
the vent solenoid slowly releases the vacuum allow-
ing throttle position to decrease. A special dump
solenoid allows immediate release of throttle posi-
tion caused by braking, cruise control switch turned
off, shifting into neutral, excessive RPM (tires spin-
ning) or ignition key off.
3.2.4 PCM OPERATING MODES
As input signals to the powertrain control module
(PCM) change, the PCM adjusts its response to
output devices. For example, the PCM must calcu-
late a different injector pulse width and ignition
timing for idle than it does for wide open throttle.
There are several different modes of operation that
determine how the PCM responds to the various
input signals.
There are two types of engine control operation:
open loopandclosed loop.
In open loop operation, the PCM receives input
signals and responds according to preset program-
ming. Inputs from the heated oxygen sensors are
not monitored.
In closed loop operation, the PCM monitors the
inputs from the heated oxygen sensors. 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 oxygen
sensor, the PCM can fine tune injector pulse width.
Fine tuning injector pulse width allows the PCM toachieve the lowest emission levels while maintain-
ing optimum fuel economy.
The engine start-up (crank), engine warm-up,
and wide open throttle modes are open loop modes.
Under most operating conditions, closed loop modes
occur with the engine at operating temperature.
IGNITION SWITCH ON (ENGINE OFF) MODE
When the ignition switch activates the fuel injec-
tion system, the following actions occur:
1. The PCM determines atmospheric air pressure
from the MAP sensor input to determine basic
fuel strategy.
2. The PCM monitors the engine coolant tempera-
ture sensor and throttle position sensor input.
The PCM modifies fuel strategy based on this
input.
When the key is in the ªonº position and the
engine is not running (zero rpm), the auto shut-
down relay and fuel pump relay are not energized.
Therefore, voltage is not supplied to the fuel pump,
ignition coil, and fuel injectors.
Engine Start-up Mode -This is an open loop
mode. The following actions occur when the starter
motor is engaged:
1. The auto shutdown and fuel pump relays are
energized. If the PCM does not receive the cam-
shaft and crankshaft signal within approxi-
mately one second, these relays are de-
energized.
2. The PCM energizes all fuel injectors until it
determines crankshaft position from the cam-
shaft and crankshaft signals. The PCM deter-
mines crankshaft position within one engine
revolution. After the crankshaft position has
been determined, the PCM energizes the fuel
injectors in sequence. The PCM adjusts the in-
jector pulse width and synchronizes the fuel
injectors by controlling the fuel injectors' ground
paths.
3. Once the engine idles within 64 rpm of its target
engine speed, the PCM compares the current
MAP sensor value with the value received dur-
ing the ignition switch on (zero rpm) mode. A
diagnostic trouble code is written to PCM mem-
ory if a minimum difference between the two
values is not found.
Once the auto shutdown and fuel pump relays
have been energized, the PCM determines the fuel
injector pulse width based on the following:
± engine coolant temperature
± manifold absolute pressure
± intake air temperature
± engine revolutions
± throttle position
4
GENERAL INFORMATION
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The PCM determines the spark advance based on
the following:
± engine coolant temperature
± crankshaft position
± camshaft position
± intake air temperature
± manifold absolute pressure
± throttle position
Engine Warm-Up Mode -This is an open loop-
mode. The PCM adjusts injector pulse width and
controls injector synchronization by controlling the
fuel injectors' ground paths. The PCM adjusts igni-
tion timing and engine idle speed. The PCM adjusts
the idle speed by controlling the idle air control
motor and spark advance.
Cruise or Idle Mode -When the engine is at
normal operating temperature, this is a closed loop
mode.
Acceleration Mode -This is a closed loop mode.
The PCM recognizes an increase in throttle position
and a decrease in manifold vacuum as engine load
increases. In response, the PCM increases the in-
jector pulse width to meet the increased load. The
A/C compressor may be de-energized for a short
period of time.
Deceleration -This is a closed loop mode. The
PCM recognizes a decrease in throttle position and
an increase in manifold vacuum as engine load
decreases. In response, the PCM decreases the
injector pulse width to meet the decreased load.
Full injector shut off may be obtained during high
speed deceleration.
Wide Open Throttle Mode -This is an open
loop mode. The throttle position sensor notifies the
PCM of a wide open throttle condition. Once a wide
open throttle is sensed, the PCM de-energizes the
A/C compressor clutch relay for 15 seconds.
3.2.5 NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems, and conditions even though they could
have malfunctions that result in driveability prob-
lems. A diagnostic code may not be displayed for the
following conditions. However, problems with these
systems may cause a diagnostic code to be displayed
for other systems. For example, a fuel pressure
problem will not register a diagnostic code directly,
but could cause a rich or lean condition. This could
cause an oxygen sensor, fuel system, or misfire
monitor trouble code to be stored in the PCM.
Engine Timing -The PCM cannot detect an
incorrectly indexed timing chain, camshaft
sprocket, or crankshaft sprocket. The PCM also
cannot detect an incorrectly indexed distributor.(*)
Fuel Pressure -Fuel pressure is controlled by
the fuel pressure regulator. The PCM cannot detecta clogged fuel pump inlet filter, clogged in-line filter,
or a pinched fuel supply.(*)
Fuel Injectors -The PCM cannot detect if a fuel
injector is clogged, the pintle is sticking, or the
wrong injectors are installed.(*)
Fuel Requirements -Poor quality gasoline can
cause problems such as hard starting, stalling, and
stumble. Use of methanol-gasoline blends may re-
sult in starting and driveability problems. See indi-
vidual symptoms and their definitions in Section
6.0 (Glossary of Terms)
PCM Grounds -The PCM cannot detect a poor
system ground. However, a diagnostic trouble code
may be stored in the PCM as a result of this
condition.
Throttle Body Air Flow -The PCM cannot
detect a clogged or restricted air cleaner inlet or
filter element.(*)
Exhaust System -The PCM cannot detect a
plugged, restricted, or leaking exhaust system.(*)
Cylinder Compression -The PCM cannot de-
tect uneven, low, or high engine cylinder compres-
sion.(*)
Excessive Oil Consumption -Although the
PCM monitors the exhaust stream oxygen content
through the oxygen sensor when the system is in a
closed loop, it cannot determine excessive oil con-
sumption.
(*)NOTE: ANY OF THESE CONDITIONS
COULD RESULT IN A RICH OR LEAN
CONDITION CAUSING AN OXYGEN SENSOR
TROUBLE CODE TO BE STORED IN THE
PCM, OR THE VEHICLE MAY EXHIBIT ONE
OR MORE OF THE DRIVEABILITY
SYMPTOMS LISTED IN THE TABLE OF
CONTENTS.
3.2.6 SKIS OVERVIEW
The Sentry Key Immobilizer System (SKIS) is an
immobilizer system design to prevent unauthorized
vehicle operation. The system consists of a Sentry
Key Immobilizer Module (SKIM), ignition key(s)
equipped with a transponder chip and engine con-
troller. When the ignition switch is turned on, the
SKIM interrogates the ignition key. If the ignition
key is ``Valid'', the SKIM sends a CCD Bus message
to the engine controller indicating the presence of a
valid igntion key. Upon receiving a ``Valid'' key
signal the PCM will allow the engine to continue to
operate.
3.2.7 SKIM ON-BOARD DIAGNOSTICS
The SKIM has been programmed to transmit and
monitor many different coded messages as well as
CCD Bus messages. This monitoring is called ``On
Board Diagnosis''.
5
GENERAL INFORMATION
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Symptom:
P-0106 BAROMETRIC PRESSURE OUT OF RANGE
When Monitored and Set Condition:
P-0106 BAROMETRIC PRESSURE OUT OF RANGE
When Monitored: With the ignition key on at less than 350 milliseconds and engine speed
at less than 255 RPM.
Set Condition: The PCM senses the voltage from the MAP sensor to be less than 2.196
volts but above 0.019 volt for 300 milliseconds
POSSIBLE CAUSES
MAP SENSOR 5V SUPPLY CIRCUIT OPEN
MAP SENSOR 5V SUPPLY CIRCUIT SHORT TO GROUND
MAP SENSOR SIGNAL CIRCUIT OPEN
MAP SENSOR SIGNAL CIRCUIT PARTIAL SHORT TO GROUND
MAP SENSOR WIRING HARNESS INTERMITTENT DEFECT
MAP SENSOR WIRING HARNESS OBSERVABLE DEFECT
MAP SENSOR DEFECTIVE
PCM DEFECTIVE (VOLTAGE HIGH)
PCM DEFECTIVE (VOLTAGE LOW)
TEST ACTION APPLICABILITY
1 Ignition On, Engine Not Running
With the DRB, read the MAP Sensor voltage.
Is the voltage below 2.2 volts?All
Ye s®Go To 2
No®Go To 11
2 Ignition Off
Disconnect the MAP Sensor Electrical Connector.
Turn the ignition on, engine not running.
Note: Check connectors - Clean/repair as necessary.
Using a Voltmeter, measure voltage of the 5-Volt Supply Circuit at the Map Sensor
Connector.
Is the voltage above 4.5 volts?All
Ye s®Go To 3
No®Go To 7
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DRIVEABILITY
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Symptom:
P-0108 MAP SENSOR VOLTAGE TOO HIGH
When Monitored and Set Condition:
P-0108 MAP SENSOR VOLTAGE TOO HIGH
When Monitored: With engine rpm above 400 but less than 1500 and closed throttle.
Set Condition: The MAP Sensor Signal voltage is greater than 4.6.
POSSIBLE CAUSES
MAP SENSOR GROUND CIRCUIT OPEN
MAP SENSOR SIGNAL CIRCUIT OPEN
MAP SENSOR DEFECTIVE
MAP SENSOR WIRING HARN AND CONN INTERMITTENT DEF
MAP SENSOR WIRING HARNESS AND CONN OBSERVABLE DEF
PCM DEFECTIVE (MAP SENSOR VOLTAGE TOO HIGH)
TEST ACTION APPLICABILITY
1 Start the engine.
With the DRB, read the MAP Sensor voltage.
Is the MAP Sensor voltage above 4.6 volts?All
Ye s®Go To 2
No®Go To 6
2 Ignition Off
Disconnect the MAP Sensor Electrical Connector.
Note: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the Sensor Signal and Sensor Ground Circuits.
Turn ignition on, use the DRB to read the MAP Sensor voltage.
Is the voltage below 1.0 volt?All
Ye s®Replace the MAP Sensor.
Perform Powertrain Verification Test VER-5A.
No®Go To 3
3 Ignition Off
Disconnect the MAP Sensor Electrical Connector.
Note: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the Sensor Signal Circuit and an engine ground.
Ignition On.
Read the MAP Sensor voltage.
Is the MAP Sensor voltage below 1.0 volt?All
Ye s®Repair the open MAP Sensor Ground Circuit.
Perform Powertrain Verification Test VER-5A.
No®Go To 4
32
DRIVEABILITY
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TEST ACTION APPLICABILITY
3 Ignition Off
Disconnect the ECT Sensor Electrical Connector.
Note: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the ECT Sensor Signal Circuit and an engine ground.
Turn the ignition on, with the engine not running.
With the DRB, read the Engine Coolant Temperature Sensor voltage.
Is the voltage below 1.0 volt?All
Ye s®Repair the open ECT Sensor Ground Circuit.
Perform Powertrain Verification Test VER-5A.
No®Go To 4
4 Ignition Off
Disconnect the ECT Sensor Connector.
Note: Check connectors - Clean/repair as necessary.
Disconnect the PCM Connector.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the ECT Sensor Signal Circuit from the PCM to the
ECT.
Is the resistance below 5.0 ohms?All
Ye s®Go To 5
No®Repair the open ECT Sensor Signal Circuit.
Perform Powertrain Verification Test VER-5A.
5 Ignition Off
If there are no potential causes remaining, the PCM is assumed to be defective.
View repair options.All
Repair
Replace the PCM.
Perform Powertrain Verification Test VER-5A.
6 Ignition On, Engine Not Running
Use the schematic as a guide and wiggle the ECT Sensor Connector & Harness.
Monitor the DRB display.
Was there any ECT Sensor voltage change?All
Ye s®Repair the Harness or Connector that caused the voltage change.
Perform Powertrain Verification Test VER-5A.
No®Go To 7
7 Ignition Off
Using the schematic as a guide, inspect the Wiring and Connectors.
Were any problems found?All
Ye s®Repair as necessary.
Perform Powertrain Verification Test VER-5A.
No®Test Complete.
41
DRIVEABILITY
P-0118 ECT SENSOR VOLTAGE TOO HIGH ÐContinued
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Symptom:
P-0122 THROTTLE POSITION SENSOR VOLTAGE LOW
When Monitored and Set Condition:
P-0122 THROTTLE POSITION SENSOR VOLTAGE LOW
When Monitored: With the ignition on.
Set Condition: The TP sensor signal voltage goes below 0.16 volt.
POSSIBLE CAUSES
TPS 5-VOLT SUPPLY CIRCUIT OPEN
TPS SIGNAL CIRCUIT SHORT TO GROUND
TPS SIGNAL CIRCUIT SHORT TO SENSOR GROUND CIRCUIT
TPS WIRING HARNESS INTERMITTENT DEFECT
TPS WIRING HARNESS OBSERVABLE DEFECT
PCM DEFECTIVE (TPS)
THROTTLE POSITION SENSOR DEFECTIVE
THROTTLE POSITION SENSOR VOLTAGE CHANGE NOT SMOOTH
TRANSMISSION CONTROL MODULE DEFECTIVE (TPS)
TEST ACTION APPLICABILITY
1 Turn key on, engine off.
With the DRB, read the Throttle Position Sensor (TP Sensor) voltage.
Is the Throttle Position Sensor voltage below 0.16 volt?All
Ye s®Go To 2
No®Go To 8
2 Ignition Off
Disconnect the Throttle Position Sensor.
Note: Check connectors - Clean/repair as necessary.
Ignition On, Engine Not Running.
Measure the voltage at the 5-Volt Supply Circuit at TPS Connector.
Is the voltage below 4.0 volts?All
Ye s®Repair the open TP Sensor 5-Volt Supply Circuit.
Perform Powertrain Verification Test VER-5A.
No®Go To 3
45
DRIVEABILITY
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TEST ACTION APPLICABILITY
3 Ignition Off
Disconnect the Throttle Position Sensor Connector.
Disconnect the Powertrain Control Module Connector.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure between the 5-volt Supply Circuit and the Throttle
Position Sensor Signal Circuit at the Throttle Position Sensor Connector.
Is the resistance below 5.0 ohms?All
Ye s®Repair the Throttle Position Sensor Signal Circuit shorted to the
5-volt Supply Circuit.
Perform Powertrain Verification Test VER-5A.
No®Go To 4
4 Turn the Ignition Off
Disconnect the TCM harness connector.
Turn the Ignition On.
Using the DRB, monitor the TP sensor voltage.
Is the voltage below 1.0 volt?All
Ye s®Replace the Transmission Control Module.
No®Go To 5
5 Ignition Off
Disconnect the Throttle Position Sensor Connector.
Note: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the Throttle Position Sensor Signal Circuit and
Sensor Ground Circuit.
Ignition on, engine not running.
Using the DRB, read the Throttle Position Sensor voltage.
Is the voltage below 1.0 volt?All
Ye s®Replace the Throttle Position Sensor.
Perform Powertrain Verification Test VER-5A.
No®Go To 6
6 Ignition Off
Disconnect the TPS Electrical Connector.
Note: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the TPS Signal Circuit and a good engine ground.
Ignition on, engine not running.
Using the DRB, read the Throttle Position Sensor voltage.
Is the voltage below 1.0 volt?All
Ye s®Repair the open Throttle Position Sensor Ground Circuit.
Perform Powertrain Verification Test VER-5A.
No®Go To 7
49
DRIVEABILITY
P-0123 THROTTLE POSITION SENSOR VOLTAGE HIGH ÐContinued
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Symptom:
P-0131 1/1 O2 SENSOR VOLTAGE SHORTED TO GROUND
When Monitored and Set Condition:
P-0131 1/1 O2 SENSOR VOLTAGE SHORTED TO GROUND
When Monitored: With the ignition key off, after the O2 Sensor cools down; and after the
next key on provided that it is a cold start (coolant temperature less than 38 degrees C
(100.4 degrees F)) and ambient temperature within 13 degrees C (7.2 degrees F) of coolant
temperature.
Set Condition: The upstream O2 Sensor Signal voltage is below 0.156 volt prior to O2
Sensor Heater test (cool down period), and O2 voltage less than 0.156 volt after the key on
in the subsequent start.
POSSIBLE CAUSES
1/1 02 SENSOR VOLTAGE LOW
1/1 O2S SIGNAL CIRCUIT SHORT TO GROUND
1/1 O2S SIGNAL CKT SHORT TO GROUND CIRCUIT
1/1 O2 SENSOR DEFECTIVE
PCM DEFECTIVE (1/1 O2S)
TEST ACTION APPLICABILITY
1 Ignition Off
Turn ignition on.
With the DRB, monitor the Upstream O2 Sensor voltage for a few minutes.
Wait three minutes or until the voltage stabilizes (between 0.4 and 0.6 volt).
With the DRB, monitor the Upstream O2 Sensor voltage.
Is the Upstream O2 Sensor voltage below 0.156 volt?All
Ye s®Go To 2
No®The condition required to set this trouble code is not present at
this time.
Perform Powertrain Verification Test VER-5A.
2 Ignition Off
Disconnect the Upstream O2 Sensor Connector.
Note: Check connectors - Clean/repair as necessary.
Key on.
With the DRB, monitor the Upstream O2 Sensor voltage.
Is the Upstream O2 Sensor voltage below 0.156 volts?All
Ye s®Go To 3
No®Replace the Upstream O2 Sensor.
Perform Powertrain Verification Test VER-5A.
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DRIVEABILITY
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