6E–87 ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Electrical Test
StepNo Ye s Va l u e ( s ) Action
9Check for short or open between the PCM and the fuel
pump relay.
Was a problem found?
—Verify repairGo to Step 10
101. Check the fuel pump relay circuit for a poor terminal
connection at the PCM.
2. If a problem is found, replace terminal as necessary.
Was a problem found?
—Verify repairGo to Step 11
11Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?—Verify repair—
121. Reconnect the fuel pump relay.
2. Disconnect the fuel pump electrical connector at the
fuel tank.
3. Using a test light connected to ground, probe the
fuel pump feed wire (harness side).
4. Command the fuel pump “ON” with Tech 2.
Did the light illuminate for 2 seconds?
—Go to Step 15Go to Step 13
131. Honk the horn to verify that the horn relay is
functioning.
2. Substitute the horn relay for the fuel pump relay.
3. Leave the test light connected as in step 12.
4. Command the fuel pump “ON” with Tech 2.
Did the test light illuminate for 2 seconds when the fuel
pump was commanded “ON?”
—Go to Step 17Go to Step 14
141. Re-connect the horn relay in its proper location.
2. Check for a short circuit, blown fuse or open circuit
between the relay and the fuel tank.
Is the action complete?
—Verify repair—
151. With the fuel pump electrical connector at the fuel
tank disconnected, connect a test light between the
feed wire and the ground wire (harness side).
2. Command the fuel pump “ON” with Tech 2.
Did the test light illuminate for 2 seconds?
—Go to Step 18Go to Step 16
16Repair the open circuit in the fuel pump ground wire.
Is the action complete?
—Verify repair—
171. Re-connect the horn relay in its proper location.
2. Replace the fuel pump relay.
Is the action complete?
—Verify repair—
18Replace the fuel pump.
Is the action complete?
—Verify repair—
6E–89 ENGINE DRIVEABILITY AND EMISSIONS
The valve or valve seat within the fuel pressure
regulator.
The fuel injector(s).
4. Fuel pressure that drops off during acceleration,
cruise, or hard cornering may case a lean condition.
A lean condition can cause a loss of power, surging,
or misfire. A lean condition can be diagnosed using
a Tech II Tech 2. If an extremely lean condition
occurs, the oxygen sensor(s) will stop toggling. The
oxygen sensor output voltage(s) will drop below 500
mV. Also, the fuel injector pulse width will increase.
IMPORTANT:Make sure the fuel system is not
operating in the “Fuel Cut-Off Mode.”
When the engine is at idle, the manifold pressure is
low (high vacuum). This low pressure (high vacuum)
is applied to the fuel pressure regulator diaphragm.
The low pressure (high vacuum) will offset the
pressure being applied to the fuel pressure regulator
diaphragm by the spring inside the fuel pressure
regulator. When this happens, the result is lower fuel
pressure. The fuel pressure at idle will vary slightly as
the barometric pressure changes, but the fuel
pressure at idle should always be less than the fuel
pressure noted in step 2 with the engine “OFF.”
16.Check the spark plug associated with a particular
fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking. If
checking the spark plug associated with a particular
fuel injector for fouling or saturation does not
determine that a particular fuel injector is leaking,
use the following procedure:
Remove the fuel rail, but leave the fuel lines and
injectors connected to the fuel rail. Refer to
Fuel Rail
Assembly
in On-Vehicle Service.
Lift the fuel rail just enough to leave the fuel injector
nozzles in the fuel injector ports.
CAUTION: In order to reduce the risk of fire and
personal injury that may result from fuel spraying on
the engine, verify that the fuel rail is positioned over
the fuel injector ports and verify that the fuel injector
retaining clips are intact.
Pressurize the fuel system by connecting a 10 amp
fused jumper between B+ and the fuel pump relay
connector.
Visually and physically inspect the fuel injector
nozzles for leaks.
17.A rich condition may result from the fuel pressure
being above 376 kPa (55 psi). A rich condition may
cause a DTC P0132 or a DTC P0172 to set.
Driveability conditions associated with rich
conditions can include hard starting (followed by
black smoke) and a strong sulfur smell in the
exhaust.20.This test determines if the high fuel pressure is due
to a restricted fuel return line or if the high fuel
pressure is due to a faulty fuel pressure regulator.
21.A lean condition may result from fuel pressure
below 333 kPa (48 psi). A lean condition may
cause a DTC P0131 or a DTC P0171 to set.
Driveability conditions associated with lean
conditions can include hard starting (when the
engine is cold ), hesitation, poor driveability, lack of
power, surging , and misfiring.
22.Restricting the fuel return line causes the fuel
pressure to rise above the regulated fuel pressure.
Command the fuel pump “ON” with Tech 2. The fuel
pressure should rise above 376 kPa (55 psi) as the
fuel return line becomes partially closed.
NOTE: Do not allow the fuel pressure to exceed 414 kPa
( 6 0 p s i ) . F u e l p r e s s u r e i n e x c e s s o f 4 1 4 k P a ( 6 0 p s i ) m a y
damage the fuel pressure regulator.
CAUTION: To reduce the risk of fire and personal
injury:
It is necessary to relieve fuel system pressure
before connecting a fuel pressure gauge. Refer to
Fuel Pressure Relief Procedure, below.
A small amount of fuel may be released when
disconnecting the fuel lines. Cover fuel line
fittings with a shop towel before disconnecting, to
catch any fuel that may leak out. Place the towel in
an approved container when the disconnect is
completed.
Fuel Pressure Relief Procedure
1. Remove the fuel cap.
2. Remove the fuel pump relay from the underhood
relay center.
3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.
Fuel Gauge Installation
1. Remove the shoulder fitting cap.
2. Install fuel gauge 5-8840-0378-0 to the fuel feed line
located in front of and above the right side valve train
cover.
3. Reinstall the fuel pump relay.
6E–234
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0502 VSS Circuit Low Input
D06RW019
Circuit Description
The vehicle speed sensor has a magnet rotated by the
transmission output shaft. Attached to the sensor is a hall
effect circuit the interacts with the magnetic field treated
by the rotating magnet. A 12-volt operating supply for the
speed sensor hall circuit is supplied from the meter fuse.
The VSS pulses to ground the 9-volt signal sent from the
powertrain control module (PCM) on the reference circuit.
The PCM interprets vehicle speed by the number of
pulses to ground per second on the reference circuit.
Conditions for Setting the DTC
Engine is running.
Engine coolant temperature is above 60C (140F).
Engine speed is between 1800 RPM and 2500 RPM.
Throttle angle is between 10% and 40%.
Engine load is greater than 50 kPa.
MAP sensor indicates greater than 50 kPa manifold
pressure.
PCM detects no VSS signal for 12.5 seconds over a
period of 25 seconds.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC
DTC P0502 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
10. To avoid backprobing the VSS and possibly
damaging a seal or terminal, the VSS output can be
tested at the point where the transmission harness
connects to the engine harness. Power and ground
are applied by jumpers to the VSS through the
connectors which are located just in front of the air
cleaner assembly. The VSS signal is monitored
with a DVM as the rear driveshaft turns. The
wheels can be turned to rotate the driveshaft, or in
2-wheels-drive vehicles the driveshaft can be turned
directly.
12. The speedometer-to-PCM VSS signal wire is
spliced to a wire leading to the cruise control
module. If a short to ground or voltage is indicated
between the PCM and speedometer, it could be on
the cruise control circuit if the vehicle is equipped
with cruise control.
6E–235 ENGINE DRIVEABILITY AND EMISSIONS
DTC P0502 – VSS Circuit Low Input
StepActionVa l u e ( s )Ye sNo
1Was the “On-Board Diagnostic (OBD) System Check”
performed?
—Go to Step 2
Go to OBD
System
Check
2Does the speedometer work?—Go to Step 10Go to Step 3
31. Disconnect the VSS connector.
2. Ignition “ON.”
3. Using a test light to battery +, probe the connector
ground wire.
Did the light illuminate?
—Go to Step 5Go to Step 4
4Repair the sensor ground.
Is the action complete?
—Verify repair—
51. Ignition “ON,” sensor disconnected.
2. Using a DVM, measure at the VSS connector
between ground and voltage supply.
Was the measurement near the specified value?
Battery
voltage
Go to Step 7Go to Step 6
6Repair the open or short to ground which may have
blown the meter fuse.
Is the action complete?
—Verify repair—
71. Ignition “ON,” VSS disconnected.
2. Using a DVM, measure at the VSS connector
between ground and the wire from the
speedometer.
Was the measurement near the specified value?
7.5-8 VGo to Step 9Go to Step 8
8Check for an open or short circuit between the
speedometer and the VSS.
Was an open or short circuit located?
—Verify repairGo to Step 9
9Replace the speedometer.
Is the action complete?
—Verify repair—
6E–247 ENGINE DRIVEABILITY AND EMISSIONS
DTC P1171 – Fuel System Lean During Acceleration
StepNo Ye s Va l u e ( s ) Action
71. Ignition “OFF.”
2. Remove the fuel pump relay and replace it with a
fused jumper which will connect the relay’s battery
terminal to the terminal leading to the fuel pump
fuse.
3. While the fuel pump is operating, use pliers to slowly
close the return line (do not exceed the first
specified value).
Using the pliers to restrict the return line, can the fuel
pressure be manipulated to exceed the second
specified value?
414 kPa
(60 psi)
325 kPa
(46 psi)
Go to
Diagnostic
Aids
Go to Step 8
8Check for:
Faulty fuel pump
Restricted fuel pump strainer (sock)
Incorrect fuel pump
Incorrect fuel being used
Hot fuel
Is the action complete?
—Verify repair—
6E–259 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P1640 Driver-1-Input High Voltage
Circuit Description
Output driver modules (ODMs) are used by the
powertrain control module (PCM) to turn “ON” many of
the current-driven devices that are needed to control
various engine and transmission functions. Each ODM is
capable of controlling up to 7 separate outputs by
applying ground to the device which the PCM is
commanding “ON.”
Unlike the Quad Driver Modules (QDMs) used in prior
model years, ODMs have the capability of diagnosing
each output circuit individually. DTC P1640 set indicates
an improper voltage level has been detected on an ODM
output.
Since A/C is an option, No A/C will cause the air
conditioning clutch relay output to always fault. If a fault is
seen on the air conditioning clutch relay output, it will not
be logged as a fault until the A/C request input interrupts a
high voltage, indicating that A/C has been installed.
Conditions for Setting the DTC
Ignition “ON.”
Engine running.
No DTC 1618.
Ignition voltage is above 13.2 volts for 4 seconds.
Output voltage does not equal ignition voltage when
output is “OFF” or output voltage is not less than 1 volt
when output is “ON.”
Above conditions occur for at least 1 second.
Action Taken When the DTC Sets
The PCM will not illuminate the malfunction indicator
lamp (MIL).
The PCM will store conditions which were present
when the DTC was set as Failure Records only. This
information will not be stored as Freeze Frame data.
Conditions for Clearing the MIL/DTC
DTC P1640 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:
Poor connection at PCM – Inspect harness connectors
for backed-out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal-to-wire connection.
Damaged harness – Inspect the wiring harness for
damage, If the harness appears to be OK, disconnect
the PCM, turn the ignition “ON” and observe a
voltmeter connected to the suspect driver circuit at the
PCM harness connector while moving connectors and
wiring harnesses relates to the MIL. A change in
voltage will indicate the location of the fault.
Poor connection at component – Examine for
damaged connectors, unplugged connector, or
damaged terminals at the following locations:
Instrument cluster harness, canister purge solenoid,
A/C clutch relay. An open ignition feed circuit at any of
these components will cause DTC P1640 to be set.
Reviewing the Failure Records vehicle mileage since the
diagnostic test last failed may help determine how often
the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.
The following PCM pins are controlled by output driver
modules (ODMs):
A13 – “Check Engine Lamp”
A14 – SVS (”Check Trans”)
B14 – A/C Clutch
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
6. The Tech 2 Driver Module Status indicates the PCM
pin that is affected.
11. The Tech 2 may indicate “short circuit” even when
the problem is an open circuit. The cause of an
open circuit may be in the component itself-lamp,
purge, solenoid, or A/C compressor relay.
13.A short to ground on the ignition side of the
component will blow the fuse. Since the fuse was
checked in Step 4, a short to ground would be
between the affected component and the PCM.
6E–260
ENGINE DRIVEABILITY AND EMISSIONS
DTC P1640 – Driver-1-Input High Voltage
StepActionVa l u e ( s )Ye sNo
1Was the “On-Board Diagnostic (OBD) System Check”
performed?
—Go to Step 2
Go to OBD
System
Check
21. Ignition “ON,”engine “OFF.”
2. Install the Tech 2.
3. Review and record Tech 2 Failure Records data.
4. Operate the vehicle within Failure Records
conditions as noted.
5. Use the Tech 2 to indicate DTC P1640.
Does the Tech 2 indicate DTC P1640?
—Go to Step 3—
3Check the fuse for the driver circuit that was shown as
faulty.
Was the fuse blown?
—Go to Step 4Go to Step 5
41. Check for a short to ground between the fuse and
the affected component.
2. Replace the fuse after making any necessary
repairs.
Is the action complete?
—Verify repair—
5Disconnect the PCM connector for the affected driver
circuit.
Is there any damage to the PCM pin or connector?
—Go to Step 6Go to Step 7
6Repair the damaged pin or terminal.
Is the action complete?
—Verify repair—
7Were either of the lamp circuits for “Check Engine” or
“Check Trans.” indicated as faulty by the Tech 2?
—Go to Step 8Go to Step 14
81. Leave the PCM connector for the lamp driver circuit
disconnected.
2. Ignition “ON.”
3. Using a DVM, check the voltage at the PCM
connector for the affected lamp driver circuit.
Was the voltage equal to the specified value?
B+Go to Step 16Go to Step 9
91. Ignition “ON.”
2. Check for battery voltage at the fuse for the affected
lamp circuit.
Was battery voltage available at the fuse?
—Go to Step 11Go to Step 10
10Repair the open circuit between the ignition switch and
the fuse.
Is the action complete?
—Verify repair—
111. Ignition “OFF.”
2. Disconnect the PCM connector for the affected
driver terminal.
3. Connect an ohmmeter between a good ground and
the PCM connector for the affected driver.
Did the ohmmeter indicate continuity?
—Go to Step 12Go to Step 13
12Repair the short to ground between the affected
component and is PCM driver terminal.
Is the action complete?
—Verify repair—
6E–261 ENGINE DRIVEABILITY AND EMISSIONS
DTC P1640 – Driver-1-Input High Voltage
StepNo Ye s Va l u e ( s ) Action
13Repair the open circuit between the fuse and the PCM
driver terminal for the affected circuit.
Is the action complete?
—Verify repair—
141. Connect the PCM.
2. Start the engine and let it idle.
3. Backprobe the affected terminal at the PCM with a
DVM.
Was the voltage equal to the specified value?
+BGo to Step 16Go to Step 15
151. Run the engine at idle.
2. Check for battery voltage at the fuse for the affected
circuit.
Was battery voltage available at the fuse?
—Go to Step 11Go to Step 10
16Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?—Verify repair—