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-0171±1/1 FUEL SYSTEM LEAN
When Monitored and Set Condition:
P-0171±1/1 FUEL SYSTEM LEAN
When Monitored: With the engine running in closed loop mode, the ambient, battery
temperature above Ð5 deg. C (20 deg. F) and altitude below 8000 ft.
Set Condition: If the PCM multiplies short term compensation by long term adaptive and
a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates
and a trouble code is stored.
POSSIBLE CAUSES
FUEL PUMP MODULE DEFECTIVE
TPS VOLTAGE CHANGE NOT SMOOTH
TPS VOLTAGE <0.92V
FUEL INLET STRAINER PLUGGED
ECT SENSOR DEFECTIVE (OUT OF CALIBRATION)
MAP SENSOR DEFECTIVE (OUT OF CALIBRATION)
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR DEFECTIVE (HIGH)
FUEL FILTER/PRESSURE REGULATOR DEFECTIVE (LOW)
FUEL PUMP CAPACITY (VOLUME) OUT OF SPECS
TEST ACTION APPLICABILITY
1 Turn ignition on.
With the DRB, read the DTC's.
Is the Global Good Trip Counter displayed and equal to zero for P0171?All
Ye s®Go To 2
No®Go To 13
2 Ignition On, Engine Not Running
With the DRB, read the TPS voltage.
While monitoring the DRB, slowly open and close the Throttle.
Is the voltage change smooth?All
Ye s®Go To 3
No®Replace the Throttle Position Sensor.
Perform Powertrain Verification Test VER-5A.
75
DRIVEABILITY
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TEST ACTION APPLICABILITY
7 Turn ignition off.
Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Remove the pressure test port cap at the fuel rail test port. Connect a fuel pressure
gauge to the test port pressure fitting on the fuel rail.
Ignition on. With the DRB, actuate the ASD Fuel System test and observe the fuel
pressure gauge.
Note: Fuel pressure specification is 49.2 psi +/- 5 psi
Choose a conclusion that best matches your fuel pressure reading.All
Below Specification
Go To 8
Within Specification
Go To 11
Above Specification
Replace the fuel filter pressure regulator.
Caution: Stop ALL Actuations.
8 Turn ignition off.
Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Raise vehicle on hoist,and disconnect the fuel pressure line at the fuel pump module.
Install speial 5/169fuel line adapter tool #6539 between disconnected fuel line and
the fuel pump module.
Attach a fuel pressure test gauge to the88T'' fitting on tool #6539.
Ignition on. With the DRB, actuate the ASD Fuel System test and observe the fuel
pressure gauge.
Note: Fuel pressure specification is 49.2 psi +/- 5 psi.
Is the fuel pressure within specification now?ALL
Ye s®Repair the restriction in the chassis fuel supply line between the
fuel tank and fuel rail.
No®Go to 9
Caution: Stop ALL Actuations.
9Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.
Is the Fuel Inlet Strainer plugged?All
Ye s®Replace the Fuel Inlet Strainer.
No®Go To 10
10 If there are no potential causes remaining, the Fuel Pump Module is assumed to be
defective.
View repair options.All
Repair
Replace the Fuel Pump Module
77
DRIVEABILITY
P-0171±1/1 FUEL SYSTEM LEAN ÐContinued
ProCarManuals.com
TEST ACTION APPLICABILITY
11 Check for any of the following conditions/mechanical problems.
ENGINE VACUUM Ð must be at least 13 inches in neutral
ENGINE VALVE TIMING Ð must be within specifications
ENGINE COMPRESSION Ð must be within specifications
ENGINE EXHAUST SYSTEM Ð must be free of any restrictions or leaks
ENGINE PVC SYSTEM Ð must flow freely
TORQUE CONVERTER STALL SPEED Ð must be within specifications
POWER BRAKE BOOSTER Ð no internal vacuum leaks
FUEL- must be free of contamination
FUEL INJECTOR Ð plugged or restricted injector; control wire not connected to
correct injector.
Are there any engine mechanical problems?All
Ye s®Repair as necessary.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST
No®Go To 12
12 Turn ignition off.
Warning: The fuel system is under constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Disconnect the fuel supply line at the fuel rail.
Connect fuel line adapter #6539(5/169) or #6631 (3/89) to the disconnected fuel supply
line. Insert the other end of the adapter into a graduated container.
Caution: Do not operate the fuel pump for more than 7 seconds in the next
step. Fuel pump module reservoir may run empty and damage to the fuel
pump may result.
Specification: A good fuel pump will deliver at least 1/4 liter of fuel in 7
seconds.
With the DRB, actuate the ASD Fuel System test for 7 seconds.
Is the fuel pump capacity within specification?All
Ye s®Test Complete.
No®Check for a kinked/damaged fuel supply line between the fuel
tank and fuel rail. If OK, replace the fuel filter/pressure regulator.
Caution: Stop ALL Actuations.
13 The conditions required to set the DTC are no longer present.
With the DRB read and record the freeze frame data and the ªFuel System Similar
Conditions Windowº data.
Utilize the data and try to duplicate the operating conditions at which the DTC was
set. Pay particular attention to the ECT and RPM for added diagnostics.
Note: Refer to any TSB's that may apply to the symptom.
Test Complete
Repair
Test Complete.
78
DRIVEABILITY
P-0171±1/1 FUEL SYSTEM LEAN ÐContinued
ProCarManuals.com
Symptom
P0172 -1/1 FUEL SYSTEM RICH
When Monitored and Set Condition:
P0172 -1/1 FUEL SYSTEM RICH
When Monitored: With the engine in closed loop mode, the ambient/battery temperature
above þ5 deg. C (20 deg. F) and altitude below 8000 ft.
Set Condition: If the PCM multiplies short term compensation by long term adaptive and
the result is below a certain value for two trips, a freeze frame is stored, the MIL
illuminates and a trouble code is stored.
POSSIBLE CAUSES
FUEL PUMP MODULE DEFECTIVE
TPS VOLTAGE CHANGE NOT SMOOTH
TPS VOLTAGE <0.92V
FUEL INLET STRAINER PLUGGED
ECT SENSOR DEFECTIVE (OUT OF CALIBRATION)
MAP SENSOR DEFECTIVE (OUT OF CALIBRATION)
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR DEFECTIVE (HIGH)
FUEL FILTER/PRESSURE REGULATOR DEFECTIVE (LOW)
TEST ACTION APPLICABILITY
1 Turn ignition on.
With the DRB, read the DTC's.
Is the DTC Specific Good Trip Counter displayed and equal to zero?All
Ye s®Go To 2
No®Go To 14
2 Ignition On, Engine Not Running
With the DRB, read the TPS voltage.
While monitoring the DRB, slowly open and close the Throttle.
Is the voltage change smooth?All
Ye s®Go To 3
No®Replace the Throttle Position Sensor.
Perform Powertrain Verification Test VER-5A.
79
ProCarManuals.com
TEST ACTION APPLICABILITY
8 Turn ignition off.
Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Remove the pressure test port cap at the fuel rail test port. Connect a fuel pressure
gauge to the test port pressure fitting on the fuel rail.
Ignition on. With the DRB, actuate the ASD Fuel System test and observe the fuel
pressure gauge.
Note: Fuel pressure specification is 49.2 psi +/þ 5 psi.
Choose a conclusion that best matches your fuel pressure reading.All
Below Specification
Go To 9
Within Specification
Go To 13
Above Specification
Replace the fuel filter/pressure regulator.
Caution: Stop ALL Actuations.
9 Check for any of the following conditions/mechanical problems.
ENGINE VACUUM Ð must be at least 13 inches in neutral
ENGINE VALVE TIMING Ð must be within specifications
ENGINE COMPRESSION Ð must be within specifications
ENGINE EXHAUST SYSTEM Ð must be free of any restrictions or leaks.
ENGINE PVC SYSTEM Ð must flow freely
TORQUE CONVERTER STALL SPEED Ð must be within specifications
POWER BRAKE BOOSTER Ð no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR Ð plugged or restricted injector; control wire not connected to
correct injector
Are there any engine mechanical problems?All
Ye s®Repair as necessary.
Perform FUEL SYSTEM/MISFIRE MONITOR VERIFICATION
TEST
No®Go To 10
10 Turn ignition off.
Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
Install special 5/169fuel line adapter tool #6539 between disconnected fuel line and
the fuel pump module.
Attach a fuel pressure test gauge to the ªT'' fitting on tool #6539.
Ignition on. With the DRB, actuate the ASD Fuel System test and observe the fuel
pressure gauge.
Note: Fuel pressure specification is 49.2 psi +/- 5 psi.
Is the fuel pressure within specification now?All
Ye s®Repair the restriction in the chassis fuel supply line between the
fuel tank and fuel rail.
No®Go to 11
Caution: Stop ALL Actuations.
81
P0172 -1/1 FUEL SYSTEM RICH ÐContinued
ProCarManuals.com
Symptom:
* CHECKING FUEL DELIVERY
POSSIBLE CAUSES
FUEL LINE RESTRICTED
FUEL FILTER DEFECTIVE
FUEL LINE RESTRICTED
FUEL PRESSURE REGULATOR DEFECTIVE
FUEL PUMP/REGULATOR ASSEMBLY DEFECTIVE
FUEL RETURN LINE DEFECTIVE
FUEL PUMP/REGULATOR ASSEMBLY DEFECTIVE
TEST ACTION APPLICABILITY
1 Ignition Off
Warning: The Fuel System must be opened and may be under high pressure.
Release the Fuel Pressure.
Connect a Fuel Pressure Gauge to test port.
Ignition On, Engine Not Running
With the DRB, actuate Fuel System. Fuel Pressure should be 43 to 53 psi.
Fuel Pressure should be 43 to 53 psi.
Is the Fuel Pressure within the specification?ENGINE - 2.4L I-4
DOHC and/or EN-
GINE - 3.3L V6
and/or ENGINE -
3.3L V6 FFV and/or
ENGINE - 3.8L V6
Ye s®Go To 2
No®Go To 5
2 Ignition Off
Note: Make sure the Gear Lever is in neutral, and the Park Brakes engaged.
Start the engine.
Monitor the Fuel Pressure Gauge in the next step.
While monitoring the pressure, momentarily snap Throttle wide open raising RPM to
above 3000.
Did the fuel pressure drop below 35 psi at all?All
Ye s®Go To 3
No®Test Complete.
3 Ignition Off
Inspect the Chassis Fuel Supply Line to the engine for a kink or restriction.
Is the line kinked or restricted?All
Ye s®Release the fuel pressure. Repair the Fuel Line as necessary.
Perform Powertrain Verification Test VER-2A.
No®Go To 4
237
DRIVEABILITY
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TEST ACTION APPLICABILITY
4 Ignition Off
Warning: The Fuel System must be opened and may be under high pressure.
Release the fuel pressure.
Remove the Fuel Pressure Gauge from the Fuel Rail.
Adjust a shop air hose to 40 psi.
Remove the Fuel Filter.
Using shop air, inspect the Fuel Filter passage by attempting to blow air through
inlet.
Is the Fuel Filter restricted?All
Ye s®Replace the Fuel Filter.
Perform Powertrain Verification Test VER-2A.
No®Replace the Fuel Pump and Regulator Assembly.
Perform Powertrain Verification Test VER-2A.
5 Ignition Off.
Warning: The Fuel System must be opened and may be under high pressure.
Release the Fuel Pressure.
Connect a Fuel Pressure Gauge to test port.
Ignition On, Engine Not Running.
With the DRB, actuate Fuel System. Fuel Pressure should be 43 to 53 psi for Gasoline
Engines and 50 to 60 psi for Flexible Fuel Vehicle.
Record the Fuel Pressure reading.
Is the Fuel Pressure above the specification?ENGINE - 2.4L I-4
DOHC and/or EN-
GINE - 3.3L V6
and/or ENGINE -
3.3L V6 FFV and/or
ENGINE - 3.8L V6
Ye s®Go To 6
No®Go To 8
6 Ignition Off
Warning: The Fuel System must be opened and may be under high pressure.
Release the fuel pressure.
Remove the Fuel Pressure Gauge from the Fuel Rail.
Remove the Fuel Return Line between the Fuel Tank and Filter.
Adjust a shop air hose to 40 psi.
Using shop air, inspect the Fuel Line by attempting to blow air through it.
Is the Fuel Return Line restricted?All
Ye s®Replace the Fuel Return Line.
Perform Powertrain Verification Test VER-2A.
No®Go To 7
7 If there are no potential causes remaining, the Fuel Pressure Regulator is assumed
to be defective.
View repair options.All
Repair
Replace the Fuel Pressure Regulator.
Perform Powertrain Verification Test VER-2A.
238
DRIVEABILITY
* CHECKING FUEL DELIVERY ÐContinued
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