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Symptom:
* CHECKING PCM POWER AND GROUND CIRCUITS
POSSIBLE CAUSES
OPEN PCM GROUND CIRCUIT AT CAVITY 10
FUSED IGNITION SWITCH OUTPUT CIRCUIT OPEN
OPEN PCM GROUND CIRCUIT AT CAVITY 50
TEST ACTION APPLICABILITY
1 Ignition Off
Disconnect the PCM Connector.
Note: Check connectors - Clean/repair as necessary.
With an Ohmmeter, measure the ground circuits at cavities 10 and 50.
Is the resistance below 5.0 ohms?All
Ye s®Go To 2
No®Repair the open ground circuit(s).
Perform Verification Test VER-2A.
2 Ignition Off
Disconnect the PCM Connector.
Note: Check connectors - Clean/repair as necessary.
Turn Ignition on.
With a Voltmeter, measure the Fused Ignition Switch Output Circuit cavity 20.
Is the voltage above 10.0 volts?All
Ye s®Go To 3
No®Repair the open Fused Ignition Switch Output Circuit.
Perform Verification Test VER-2A.
3 Ignition Off
Disconnect the Powertrain Control Module Connector.
Note: Check connectors - Clean/repair as necessary.
Turn Ignition on.
Using a voltmeter, probe the fused B (+) circuit 46.
Is the voltage above 10.0 volts?All
Ye s®Test Complete.
No®Repair the open fused B (+) circuit.
Perform Verification Test VER-2A.
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Symptom:
* CHECKING SECONDARY IGNITION
POSSIBLE CAUSES
SECONDARY IGNITION OUT OF SPECIFICATION
IGNITION COIL DEFECTIVE
SECONDARY IGNITION SYSTEM DEFECTIVE (WATER TEST)
TEST ACTION APPLICABILITY
1 Ignition Off.
Connect a suitable Engine Analyzer to the Engine.
Start Engine.
Allow Engine to idle.
Note: If the Engine will not idle, maintain a constant RPM above idle.
Note: Set the Scope to read, display or parade pattern.
Follow the equipment manufacturer's procedure for pattern analysis.
Is the secondary ignition pattern ok?All
Ye s®Go To 2
No®Repair the indicated component in the Secondary Ignition Sys-
tem.
Perform Powertrain Verification Test VER-2A.
2 Ignition Off
Connect a suitable Engine Analyzer to the engine.
Start the Engine and allow it to idle.
Note: If the engine will not idle, maintain a constant RPM above idle.
Set scope to read display or parade pattern.
Follow the equipment manufacturer's procedure for pattern analysis.
Note: Do not spray the Inductive Pickup.
With a spray bottle, spray the Ignition Cables with water and monitor Ignition
Pattern.
Did the Ignition Pattern change?All
Ye s®Repair the indicated component in the Secondary Ignition Sys-
tem.
Perform Powertrain Verification Test VER-2A.
No®Go To 3
3 Ignition Off
Connect a suitable Engine Analyzer to the engine.
Start the engine and allow it to idle.
Note: If the engine will not idle, maintain a constant RPM above idle.
Note: Set the scope to read display or parade pattern.
Follow the equipment manufacturer's procedure for pattern analysis.
Momentarily remove and reinstall the Spark Plug Wires.
While disconnecting each wire, observe the secondary KV line.
Is the open circuit Secondary voltage at least 25KV?All
Ye s®Test Complete.
No®Replace the Ignition Coil.
Perform Powertrain Verification Test VER-2A.
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Symptom:
* CHECKING THE ENGINE MECHANICAL SYSTEMS
POSSIBLE CAUSES
CHECKING ENGINE MECHANICAL SYSTEMS
TEST ACTION APPLICABILITY
1 At this point in the diagnostic test procedure, you have determined that all of the
engine electrical systems are operating as designed; therefore, they are not the cause
of the driveability problem.
The following additional items should be checked as possible mechanical causes of
the problem:
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
CAMSHAFT LOBES - check for abnormal wear
CRANK SENSOR PICK-UP - check crankshaft slots for debris/deterioration
ENGINE EXHAUST SYSTEM - must be free of any restrictions
ENGINE PCV SYSTEM - must flow freely
ENGINE DRIVE SPROCKETS - must be properly positioned
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connected to
correct injector
Note: If you came to this test from the oxygen sensor, and the rich or lean
condition is not caused by one of the first items above, replace the power-
train control module and perform TEST VER-2A (Road Test Verification).
Always look for any Technical Service Bulletins that may relate to the problem.
Did you come from an Oxygen Sensor rich or lean condition test?All
Ye s®Replace the Powertrain Control Module.
Perform Powertrain Verification Test VER-2A.
No®Test Complete.
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Symptom:
* CHECKING THROTTLE POSITION SENSOR CALIBRATION
POSSIBLE CAUSES
TPS VOLTAGE CHANGE NOT A SMOOTH TRANSITION
TPS VOLTAGE ABOVE 1.5 V WITH THROTTLE CLOSED
THROTTLE CABLE AND BODY BINDING OR RESTRICTED
TPS VOLTAGE BELOW 3.4 V AT WIDE OPEN THROTTLE
TEST ACTION APPLICABILITY
1 Ignition Off
Check the Throttle Cable and Body for binding or restrictions.
Note: Also check Speed Control Cable if equipped.
Is there any binding or restriction?All
Ye s®Repair as necessary.
Perform Verification Test VER-2A.
No®Go To 2
2 Ignition On, Engine Not Running
While slowly opening the Throttle from closed to wide open, monitor the Throttle
Position Sensor voltage at the DRB.
Was the voltage change a smooth transition?All
Ye s®Go To 3
No®Replace Throttle Position Sensor.
Perform Verification Test VER-2A.
3 Ignition On, Engine Not Running
With the DRB, read the Throttle Position Sensor voltage.
Note: Throttle must be fully closed and against the Throttle Stop.
Is the voltage 1.5 V or less with the Throttle closed?All
Ye s®Go To 4
No®Replace Throttle Position Sensor.
Perform Verification Test VER-2A.
4 Was the maximum voltage at least 3.4 volts at wide open Throttle? All
Ye s®Test Complete.
No®Replace Throttle Position Sensor.
Perform Verification Test VER-2A.
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Symptom:
* CHECKING THE A/C PRESSURE SENSOR SIGNAL
POSSIBLE CAUSES
A/C PRESSURE SENSOR 5-VOLT SUPPLY CIRCUIT OPEN
HIGH RESISTANCE IN THE A/C PRESSURE SENSOR SIGNAL CKT
TEST ACTION APPLICABILITY
1 Turn the ignition on.
Using the DRB, read the trouble codes.
Are any A/C Pressure sensor trouble codes set?All
Ye s®Go to the A/C Pressure sensor trouble code.
No®Go To 2
2 Turn the ignition off.
Disconnect the A/C Pressure Sensor harness connector.
Turn the ignition on.
Using a voltmeter, measure the A/C Pressure Sensor 5±volt supply circuit.
Is the voltage above 4.8 volts?All
Ye s®Go To 3
No®Repair the open in the A/C Pressure Sensor 5±volt supply circuit.
Perform Powertrain Verification Test VER-2A.
3 Turn the ignition on.
Using the DRB, monitor the A/C Pressure voltage.
Disconnect the A/C Pressure Sensor harness connector.
Is the voltage above 4.8 volts?All
Ye s®Test Complete.
No®Repair the high resistance in the A/C Pressure Sensor Signal
circuit.
Perform Powertrain Verification Test VER-2A.
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Symptom List:
P-1595 SPEED CONTROL SOLENOID CIRCUITS
P-1683 SPEED CONTROL POWER RELAY OR S/C 12V DRIVER
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P-1595 SPEED CONTROL SOLE-
NOID CIRCUITS.
When Monitored and Set Condition:
P-1595 SPEED CONTROL SOLENOID CIRCUITS
When Monitored: Speed control on, vehicle speed > 25 mph, RPM < 5440, brake not
applied. For an automatic transmission, in drive mode. For a manual transmission, the
clutch not depressed.
Set Condition: The powertrain control module (PCM) actuates the vacuum and vent
solenoid but they do not respond.
P-1683 SPEED CONTROL POWER RELAY OR S/C 12V DRIVER
When Monitored: Speed control on, vehicle speed > 25 mph, RPM < 5440, brake not
applied. For an automatic transmission, in drive mode. For a manual transmission, the
clutch not depressed.
Set Condition: The powertrain control module (PCM) actuates the vacuum and vent
solenoids but they do not respond.
POSSIBLE CAUSES
S/C BRAKE SWITCH OUTPUT CIRCUIT OPEN
S/C BRAKE SWITCH OUTPUT CIRCUIT SHORTED TO GROUND
S/C VACUUM SOLENOID CONTROL CIRCUIT OPEN
S/C VENT SOLENOID CONTROL CIRCUIT OPEN
SPEED CONTROL POWER SUPPLY CIRCUIT OPEN
SPEED CONTROL SERVO GROUND CIRCUIT OPEN
BRAKE SWITCH DEFECTIVE
SPEED CONTROL SERVO DEFECTIVE
PCM DEFECTIVE (SC SOLENOID CIRCUIT)
PCM DEFECTIVE (SPEED CONTROL P/S CIRCUIT)
BRAKE SWITCH NEEDS TO BE ADJUSTED
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TEST ACTION APPLICABILITY
1 Ignition Off
Note: A misadjusted Brake Switch can cause this code to set.
Does the Brake Switch need to be adjusted?All
Ye s®Adjust Brake Switch as necessary.
No®Go To 2
2 Ignition Off
Disconnect the Speed Control Servo 4-Way Connector.
Note: Check connectors - Clean/repair as necessary.
Note: Ensure the Brake pedal is not depressed during the following steps.
Engine off. Ignition key on and S/C On/Off Switch ON.
Using a Voltmeter, measure the voltage of the S/C Brake Switch Output Circuit at
Speed Control Servo Connector.
Is the voltage above 10.0 volts?All
Ye s®Go To 3
No®Go To 10
3 Ignition off.
Disconnect the Speed Control Servo Connector.
Note: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure resistance of the Gnd Circuit at Servo Connector.
Is the resistance below 5.0 ohms?All
Ye s®Go To 4
No®Repair the open Ground Circuit.
Perform Powertrain Verification Test VER-4A.
4 Ignition off
Disconnect the Powertrain Control Module.
Note: Check connectors - Clean/repair as necessary.
Note: Ensure the Brake pedal is not depressed during the following steps.
With an ohmmeter, test the resistance from the S/C Power Supply Circuit to the S/C
Vent Solenoid at PCM.
Is the resistance between 35 ohms and 55 ohms?All
Ye s®Go To 5
No®Go To 7
5 Ignition off
Disconnect Powertrain Control Module.
Note: Check connectors - Clean/repair as necessary.
Note: Ensure the Brake Pedal is not depressed during the following steps.
With an ohmmeter, test the resistance from the S/C Power Supply Circuit to the S/C
Vacuum Solenoid Control at PCM.
Is the resistance between 35 ohms and 55 ohms?All
Ye s®Go To 6
No®Go To 7
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P-1595 SPEED CONTROL SOLENOID CIRCUITS ÐContinued
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TEST ACTION APPLICABILITY
6 Ignition off.
If there are no potential causes remaining, the Powertrain Control Module is
assumed to be defective.
View repair options.All
Repair
Replace the PCM.
Perform Powertrain Verification Test VER-4A.
7 Ignition off.
Disconnect the Powertrain Control Module.
Disconnect Speed Control Servo 4-way Connector.
Note: Check connectors - Clean/repair as necessary.
With an ohmmeter, test the resistance of the SC Vacuum Solenoid Control Circuit
from the PCM to the Servo Connector.
Is the resistance below 5.0 ohms?All
Ye s®Go To 8
No®Repair the open Speed Control Vacuum Solenoid Control Circuit.
Perform Powertrain Verification Test VER-4A.
8 Ignition off.
Disconnect the PCM.
Disconnect Speed Control Servo 4-way Connector.
Note: Check connectors - Clean/repair as necessary.
With an ohmmeter, test the resistance of the S/C Vent Solenoid Control Circuit from
the PCM to the Servo Connector.
Is the resistance below 5.0 ohms?All
Ye s®Go To 9
No®Repair the open Speed Control Vent Solenoid Control Circuit.
Perform Powertrain Verification Test VER-4A.
9 Ignition off.
If there are no potential causes remaining, the Speed Control Servo is assumed to be
defective.
View repair options.All
Repair
Replace the Speed Control Servo.
Perform Powertrain Verification Test VER-4A.
10 Ignition off.
Disconnect the Brake Switch Connector.
Note: Check connectors - Clean/repair as necessary.
Key and S/C On.
Using a Voltmeter, probe Speed Control Power Supply Ckt at the Brake Sw
Connector.
Is the voltage above 10.0 volts?All
Ye s®Go To 11
No®Go To 14
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P-1595 SPEED CONTROL SOLENOID CIRCUITS ÐContinued
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