Page 1413 of 4284

Symptom:
*CHECKING THE ENGINE MECHANICAL SYSTEMS
POSSIBLE CAUSES
CHECKING ENGINE MECHANICAL SYSTEMS
TEST ACTION APPLICABILITY
1NOTE: The following items should be checked as a possible cause of a
Driveability or No-Start problem.
WARNING: Do not attempt to remove or separate high pressure fuel line.
Attempting to do so could result in severe bodily injury or death.
Engine Valve Timing - must be within specification
Engine Compression - must be within specifications
Camshaft Lobes - check for abnormal wear
Camshaft Position Sensor - check the camshaft position sensor tooth for debris and
deterioration
Crankshaft Position Sensor - check the crankshaft tone wheel for debris and
deterioration
Engine Exhaust System - must be free of any restriction
Engine Drive Sprocket - must be properly positioned
Power Brake Booster - must be free of any vacuum leaks
Fuel - must have adequate supply and must be free of contamination and gasoline
Fuel Injectors - must not be plugged or restricted
Fuel Injection Pump - must be producing the correct output volume and pressure
Inspect the Fuel Lines, Fuel Filter and Fuel Pressure Relief Valve for signs of
restriction and leaks
NOTE: Check for any Technical Service Bulletins that may relate to the
problem.
Are there any problems evident?All
Ye s®Repair as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No®Test Complete.
194
DRIVEABILITY - DIESEL
Page 1414 of 4284

Symptom:
*CHECKING THE GLOW PLUG OPERATION
POSSIBLE CAUSES
CHECKING THE GLOW PLUGS
FUSED B+ CIRCUIT OPEN
GLOW PLUG RELAY OUTPUT CIRCUIT SHORTED TO VOLTAGE
GLOW PLUG RELAY OUTPUT CIRCUIT SHORTED TO GROUND
GLOW PLUG RELAY OUTPUT CIRCUIT OPEN
GLOW PLUG RELAY
TEST ACTION APPLICABILITY
1 Turn the ignition off.
Disconnect the Glow Plug harness connectors for all cylinders.
Turn the ignition on.
With the DRB, actuate the Glow Plug Relay.
Using a 12-volt test light connected to ground, probe each Glow Plug harness
connector during actuator test.
Does the test light cycle on and off for each circuit during the actuator test?All
Ye s®Go To 2
No®Go To 3
2 Refer to the Service Information and perform the Glow Plug Test.
Are all Glow Plugs operating properly?All
Ye s®Test Complete.
No®Replace the Glow Plug(s) as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
3NOTE: If the Glow Plug Relay fuse or fuselink is open, refer to the system
schematics for all circuits that are powered by the Glow Plug Relay fuse or
fuselink to determine the cause of the blown fuse/fuselink.
Remove the Glow Plug Relay.
Using a 12-volt test light connected to ground, probe the Fused B+ circuit in the Glow
Plug Relay connector, cavity 30 in the IPM.
Does the test light illuminate brightly?All
Ye s®Go To 4
No®Repair the Fused B+ (Fuse/Fuselink) circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
4 Turn the ignition off.
Disconnect all the Glow Plug harness connectors.
Remove the Glow Plug Relay.
Turn the ignition on.
Measure the voltage on the Glow Plug Relay Output circuit.
Is the voltage above 1.0 volt?All
Ye s®Repair the Glow Plug Relay Output circuit for a short to voltage.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 5
195
DRIVEABILITY - DIESEL
Page 1415 of 4284

TEST ACTION APPLICABILITY
5 Turn the ignition off.
Disconnect all the Glow Plug harness connectors.
Remove the Glow Plug Relay.
Measure the resistance between ground and the Glow Plug Relay Output circuit.
Is the resistance above 100k ohms?All
Ye s®Go To 6
No®Repair the Glow Plug Relay Output circuit for a short to ground.
Inspect the fuse or fuselink and replace as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
6 Turn the ignition off.
Disconnect all the Glow Plug harness connectors.
Remove the Glow Plug Relay.
Connect a jumper wire across Glow Plug Relay connector cavities 30 and 87.
Using a 12-volt test light connected to ground, check the Glow Plug Relay Output
circuit at each Glow Plug harness connector.
Is the test light on at each Glow Plug harness connector?All
Ye s®Go To 7
No®Repair the Glow Plug Relay Output circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
7 Refer to the Service Information and perform the Glow Plug Test.
Are all Glow Plugs operating properly?All
Ye s®Go To 8
No®Replace the Glow Plug(s) as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
8 If there are no possible causes remaining, view repair. All
Repair
Replace the Glow Plug Relay.
Perform ROAD TEST VERIFICATION - VER-2.
196
DRIVEABILITY - DIESEL
*CHECKING THE GLOW PLUG OPERATION ÐContinued
Page 1416 of 4284

Symptom:
*CHECKING THE LIFT PUMP MOTOR OPERATION
POSSIBLE CAUSES
LIFT PUMP OUTPUT TEST
FUSED B+ CIRCUIT OPEN
LIFT PUMP RELAY
LIFT PUMP RELAY OUTPUT CIRCUIT SHORTED TO VOLTAGE
LIFT PUMP RELAY OUTPUT CIRCUIT SHORTED TO GROUND
LIFT PUMP RELAY OUTPUT CIRCUIT OPEN
LIFT PUMP GROUND CIRCUIT OPEN
LIFT PUMP MOTOR
TEST ACTION APPLICABILITY
1NOTE: If any Fuel Lift Pump DTCs are present, diagnose the DTCs first.
Turn the ignition on.
With the DRB, actuate the Lift Pump Relay.
Gain access to the Lift Pump Motor to determine if it is cycling on and off.
Does the Lift Pump Motor cycle on and off?All
Ye s®Go To 2
No®Go To 3
2NOTE: The Lift Pump fuel output must be sufficient to prime the Injector
Pump.
Refer to the Service Information to test the Lift Pump pressure and volume output.
Did the Lift Pump pass the Lift Pump pressure and volume test?All
Ye s®Test Complete.
No®Repair as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
3NOTE: If the Lift Pump Relay fuse is open, refer to the system schematics
for all circuits that are powered by the Lift Pump Relay fuse to determine
the cause of the blown fuse.
Remove the Lift Pump Relay from the IPM.
Using a 12-volt test light connected to ground, probe the Fused B+ circuit in the Lift
Pump Relay connector in the IPM.
Does the test light illuminate brightly?All
Ye s®Go To 4
No®Repair the Fused B+ (Fuse) circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
197
DRIVEABILITY - DIESEL
Page 1418 of 4284
TEST ACTION APPLICABILITY
9 If there are no possible causes remaining, view repair. All
Repair
Replace the Lift Pump Motor in accordance with the Service
Information.
Perform ROAD TEST VERIFICATION - VER-2.
199
DRIVEABILITY - DIESEL
*CHECKING THE LIFT PUMP MOTOR OPERATION ÐContinued
Page 1421 of 4284

TEST ACTION APPLICABILITY
4 Turn the ignition on.
With the DRBIIItin Sensors, read the Vehicle Speed Sensor signal.
Have an assistant drive the vehicle while you are observing the Vehicle Speed Signal
on the DRB.
While observing vehicle speed signal note any rapid changes (signal drop-outs) in the
reading that do not correspond with actual vehicle speed.
Is the DRB displaying an accurate Vehicle Speed Signal?All
Ye s®Go To 5
No®Refer to symptom list for problems related to the Vehicle Speed
Sensor.
Perform SPEED CONTROL VERIFICATION - VER-4.
5 Turn the ignition on.
With the DRBIIItin Inputs/Outputs, read the Primary and Secondary switch states
while pressing and releasing the Brake Pedal several times.
Did the DRB indicate the correct brake pedal state when pressing and releasing the
Brake Pedal?All
Ye s®Go To 6
No®Refer to symptom list for problems related to Brake Switch input.
Perform SPEED CONTROL VERIFICATION - VER-4.
6 Turn the ignition on.
With the DRBIIItin Inputs/Outputs, read the Clutch switch states while pressing
and releasing the Clutch Pedal several times.
Did the DRB indicate the correct clutch pedal state when pressing and releasing the
Clutch Pedal?All
Ye s®Go To 7
No®Go To 8
7WARNING: WHEN THE ENGINE IS OPERATING, DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE
PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?All
Ye s®Repair as necessary.
Perform SPEED CONTROL VERIFICATION - VER-4.
No®Replace and program the ECM in accordance with the Service
Information.
Perform SPEED CONTROL VERIFICATION - VER-4.
202
DRIVEABILITY - DIESEL
*CHECKING THE SPEED CONTROL OPERATION ÐContinued
Page 1422 of 4284

TEST ACTION APPLICABILITY
8 Turn the ignition off.
Disconnect the Clutch Pedal Switch harness connector.
Turn the ignition on.
With the DRBIIItin Inputs/Outputs, read the Clutch Switch state while using a
jumper wire to connect the Clutch Pedal Switch Sense circuit to ground at the Clutch
Pedal Switch harness connector.
NOTE: Leave jumper connected to ground for 5 seconds then disconnect
jumper and note DRB reading for both conditions.
Does the DRB display RELEASED and PRESSED?All
Ye s®Replace the Clutch Pedal Switch.
Perform SPEED CONTROL VERIFICATION - VER-4.
No®Go To 9
9 Turn the ignition off.
Disconnect the Clutch Pedal Switch harness connector.
Measure the resistance of the Clutch Pedal Switch Sense circuit.
Is the resistance below 10.0 ohms?All
Ye s®Go To 10
No®Repair the Clutch Pedal Switch Sense circuit for an open.
Perform SPEED CONTROL VERIFICATION - VER-4.
10 Turn the ignition off.
Disconnect the Clutch Pedal Switch harness connector.
Disconnect the ECM harness connectors.
Measure the resistance between ground and the Clutch Pedal Switch Sense circuit.
Is the resistance below 1000 ohms?All
Ye s®Repair the Clutch Pedal Switch Sense circuit for a short to
ground.
Perform SPEED CONTROL VERIFICATION - VER-4.
No®Replace and program the ECM in accordance with the Service
Information.
Perform SPEED CONTROL VERIFICATION - VER-4.
203
DRIVEABILITY - DIESEL
*CHECKING THE SPEED CONTROL OPERATION ÐContinued
Page 1423 of 4284

Symptom:
*CHECKING THE VEHICLE SPEED SIGNAL
POSSIBLE CAUSES
VEHICLE SPEED SENSOR SIGNAL CIRCUIT SHORTED TO SENSOR GROUND
CHECK FOR VSS DTC
IGNITION SWITCH OUTPUT CIRCUIT OPEN
SPEEDOMETER PINION AND DRIVE TEETH DAMAGED
VEHICLE SPEED SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
VEHICLE SPEED SENSOR SIGNAL CIRCUIT SHORTED TO VOLTAGE
ENGINE CONTROL MODULE - SHORTED TO VOLTAGE
VEHICLE SPEED SENSOR SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
VEHICLE SPEED SENSOR
ENGINE CONTROL MODULE - INTERNAL FAULT
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, select Engine, then Sensors.
While an assistant is test driving the vehicle, note the Vehicle Speed reading on the
DRB.
While reading the VSS Signal, note any rapid changes (signal drop-outs) that do not
correspond with actual vehicle speed.
Does the DRB display an accurate vehicle speed reading?All
Ye s®Test Complete.
No®Go To 2
2 Turn the ignition on.
With the DRB, read ECM DTCs.
Are any VSS DTCs present?All
Ye s®Refer to symptom list for problems related to VSS DTCs.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 3
3 Turn the ignition off.
Remove the Vehicle Speed Sensor.
Inspect the Speedometer Pinion and drive teeth on the Output Shaft (located in the
transmission).
Inspect the VSS for metal debris and damage to the Sensor and connector.
Are both components OK?All
Ye s®Go To 4
No®Repair or replace the Speedometer Pinion or internal components
as necessary in accordance with the Service Information.
Perform ROAD TEST VERIFICATION - VER-2.
204
DRIVEABILITY - DIESEL