
Symptom List:
P2066-MASS AIR FLOW SENSOR PLAUSIBILITY AIR MASS TOO
HIGH
P2066-MASS AIR FLOW SENSOR PLAUSIBILITY AIR MASS TOO
LOW
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2066-MASS AIR FLOW SENSOR
PLAUSIBILITY AIR MASS TOO HIGH.
When Monitored and Set Condition:
P2066-MASS AIR FLOW SENSOR PLAUSIBILITY AIR MASS TOO HIGH
When Monitored: With the engine running.
Set Condition: The ECM detects excessive air flow from the MAF Sensor.
P2066-MASS AIR FLOW SENSOR PLAUSIBILITY AIR MASS TOO LOW
When Monitored: With the engine running.
Set Condition: The ECM detects low air flow from the MAF Sensor.
POSSIBLE CAUSES
AIR FILTER
AIR RESTRICTION
CHECKING FOR AIR LEAKS
MASS AIRFLOW SENSOR
INTERMITTENT CONDITION
153
DRIVEABILITY - DIESEL

TEST ACTION APPLICABILITY
1NOTE: If DTC P1611, P2306 or P2332 is present with this DTC, diagnose
DTCs P1611, P2306 or P2332 before diagnosing this DTC.
NOTE: Inspect all air intake and turbocharger related tubes for damage,
restriction or poor connection. Any of these conditions can cause a this DTC
to set.
NOTE: If the ECM detects and stores a DTC, the ECM also stores the
engine/vehicle operating conditions under which the DTC was set. Some of
these conditions are displayed on the DRB at the same time the DTC is
displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to
duplicate these conditions may assist when checking for an active DTC.
Turn the ignition on.
With the DRBIIIt, erase the ECM DTCs.
Test drive the vehicle.
With the DRBIIIt, read the ECM DTCs.
Does the DRB III display a Mass Air Flow Sensor DTC?All
Ye s!Go To 2
No!Go To 5
2 Turn the ignition off.
Remove and inspect the Air Filter for soiling or excessive dirt and debris which may
cause air flow restriction.
Were any of these problems found?All
Ye s!Replace the Air Filter element.
Perform ROAD TEST VERIFICATION - VER-2.
No!Go To 3
3NOTE: Inspect all air intake and turbocharger related tubes for damage,
restriction or poor connection. Any of these conditions can cause a this DTC
to set.
NOTE: Inspect the exhaust system and related tubes for damage, restriction
or poor connection. Any of these conditions can cause a this DTC to set.
Turn the ignition off.
Inspect the intake system, exhaust system and related tubes and connections.
Were any problems found?All
Ye s!Repair or replace as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No!Go To 4
4 Turn the ignition off.
Remove the Intake Air Temperature Sensor.
Connect smoke machine 84-04 to the Intake Air Temperature Sensor port in the
intake duct and begin injecting smoke into the intake system.
Observe all intake system components for evidence of smoke leakage.
Is there evidence of smoke leakage?All
Ye s!Repair or replace as necessary.
Perform ROAD TEST VERIFICATION - VER-2.
No!Replace the MAF Sensor.
Perform ROAD TEST VERIFICATION - VER-2.
154
DRIVEABILITY - DIESEL
P2066-MASS AIR FLOW SENSOR PLAUSIBILITY AIR MASS TOO HIGH Ð
Continued

Symptom List:
P2100-FUEL PUMP RELAY CIRCUIT OPEN CIRCUIT
P2100-FUEL PUMP RELAY CIRCUIT SHORTED TO GROUND
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2100-FUEL PUMP RELAY
CIRCUIT OPEN CIRCUIT.
POSSIBLE CAUSES
INTERMITTENT CONDITION
ENGINE CONTROL RELAY OUTPUT CIRCUIT OPEN
FUEL LIFT PUMP RELAY
FUEL LIFT PUMP RELAY CONTROL CIRCUIT SHORTED TO GROUND
FUEL LIFT PUMP RELAY CONTROL CIRCUIT OPEN
ENGINE CONTROL MODULE
TEST ACTION APPLICABILITY
1NOTE: If the ECM detects and stores a DTC, the ECM also stores the
engine/vehicle operating conditions under which the DTC was set. Some of
these conditions are displayed on the DRB at the same time the DTC is
displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to
duplicate these conditions may assist when checking for an active DTC.
Turn the ignition on.
With the DRBIIIt, erase the ECM DTCs.
Crank and attempt to start the engine several times.
With the DRBIIIt, read the active ECM DTCs.
Did this DTC set again?All
Ye s!Go To 2
No!Go To 6
2 Turn the ignition off.
Remove the Fuel Lift Pump Relay.
Turn the ignition on.
Using a 12-volt test light connected to ground, check the Engine Control Relay
Output circuit.
Did the test light illuminate brightly?All
Ye s!Go To 3
No!Refer to Checking the ECM Power and Grounds for the related
symptom(s).
Perform ROAD TEST VERIFICATION - VER-2.
157
DRIVEABILITY - DIESEL

Symptom List:
P2100-FUEL PUMP RELAY CIRCUIT SHORTED TO VOLTAGE
P2100-FUEL PUMP RELAY EXCESSIVE CURRENT
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2100-FUEL PUMP RELAY
CIRCUIT SHORTED TO VOLTAGE.
POSSIBLE CAUSES
INTERMITTENT CONDITION
FUEL LIFT PUMP RELAY
FUEL LIFT PUMP RELAY CONTROL CIRCUIT SHORTED TO VOLTAGE
ENGINE CONTROL MODULE
TEST ACTION APPLICABILITY
1NOTE: If the ECM detects and stores a DTC, the ECM also stores the
engine/vehicle operating conditions under which the DTC was set. Some of
these conditions are displayed on the DRB at the same time the DTC is
displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to
duplicate these conditions may assist when checking for an active DTC.
Turn the ignition on.
With the DRB, actuate the Fuel Lift Pump Relay.
Does the Fuel Lift Pump Relay cycle on and off?All
Ye s!Go To 2
No!Go To 3
2WARNING: 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.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRB
parameters related to the DTC while wiggling the wiring harness. Look for param-
eter values to change and/or a DTC to set.
Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the
conditions under which the DTC was set.
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 ROAD TEST VERIFICATION - VER-2.
No!Test Complete.
159
DRIVEABILITY - DIESEL

Symptom List:
P2104-STARTER RELAY CIRCUIT SHORT CIRCUIT
P2152-STARTER RELAY CIRCUIT SHORT TO GROUND
P2153-STARTER RELAY CIRCUIT OPEN OR SHORTED TO VOLT-
AGE
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2104-STARTER RELAY CIR-
CUIT SHORT CIRCUIT.
When Monitored and Set Condition:
P2104-STARTER RELAY CIRCUIT SHORT CIRCUIT
When Monitored: During engine crank attempt.
Set Condition: The ECM detects too much current on the Starter Motor Relay Control
circuit.
POSSIBLE CAUSES
CHECKING THE ENGINE CONTROL RELAY SYSTEM
INTERMITTENT CONDITION
SUBSTITUTE STARTER RELAY
STARTER RELAY CONTROL CIRCUIT SHORTED TO GROUND
STARTER RELAY CONTROL CIRCUIT SHORTED TO VOLTAGE
ENGINE CONTROL MODULE
STARTER RELAY CONTROL CIRCUIT OPEN
TEST ACTION APPLICABILITY
1NOTE: If the ECM detects and stores a DTC, the ECM also stores the
engine/vehicle operating conditions under which the DTC was set. Some of
these conditions are displayed on the DRB at the same time the DTC is
displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to
duplicate these conditions may assist when checking for an active DTC.
Turn the ignition on.
With the DRB, erase ECM DTCs.
Attempt to start the engine several times, pausing for at least 10 seconds between
each cycle.
Turn the ignition on.
With the DRB, read ECM DTCs.
Did this DTC set again?All
Ye s!Go To 2
No!Go To 8
161
DRIVEABILITY - DIESEL

TEST ACTION APPLICABILITY
2NOTE: If DTC P1611, P2306 or P2332 is present with this DTC, diagnose
DTCs P1611, P2306 or P2332 before diagnosing this DTC.
NOTE: Check the ECM for other ECM DTC's related to circuits that are
open, shorted to ground or low voltage problems.
Does the DRB also display these type of DTC's?All
Ye s!Go To 3
No!Go To 4
3 Turn the ignition off.
Disconnect the ECM harness connectors.
Turn the ignition on.
Connect a jumper wire between ground and the Engine Control Relay Signal circuit
in ECM C2 harness connector cavity 44.
Using a 12-volt test light connected to ground, check the Fused Engine Control Relay
Output circuits at the ECM C2 harness connector cavities 1, 3 and 5.
Does the test light illuminate brightly for each circuit?All
Ye s!Go To 4
No!Refer to symptom list and perform Checking the ECM Power and
Grounds.
Perform ROAD TEST VERIFICATION - VER-2.
4 Turn the ignition off.
Install a substitute relay in place of the Starter Relay.
Turn the ignition on.
With the DRBIIIt, erase DTCs.
Attempt to start the engine several times, pausing for at least 10 seconds between
each cycle.
Turn the ignition on.
With the DRB, read ECM DTCs.
Did this DTC set again?All
Ye s!Go To 5
No!Replace the Starter Relay.
Perform ROAD TEST VERIFICATION - VER-2.
5 Turn the ignition off.
Remove the Starter Relay.
Disconnect the ECM harness connectors.
Measure the resistance of the Starter Relay Control circuit.
Is the resistance below 10.0 ohms?All
Ye s!Go To 6
No!Repair the Starter Relay Control circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
6 Turn the ignition off.
Remove the Starter Relay.
Disconnect the ECM harness connectors.
Measure the resistance between ground and the Starter Relay Control circuit.
Is the resistance above 1000 ohms?All
Ye s!Go To 7
No!Repair the Starter Relay Control circuit for a short to ground.
Perform ROAD TEST VERIFICATION - VER-2.
162
DRIVEABILITY - DIESEL
P2104-STARTER RELAY CIRCUIT SHORT CIRCUIT ÐContinued

Symptom List:
P2110-BOOST PRESSURE SERVO MOTOR CIRCUIT SHORT CIR-
CUIT
P2112-BOOST PRESSURE SERVO MOTOR CIRCUIT EXCESSIVE
CURRENT
P2526-BOOST PRESSURE SERVO MOTOR SHORT TO VOLTAGE
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2110-BOOST PRESSURE
SERVO MOTOR CIRCUIT SHORT CIRCUIT.
When Monitored and Set Condition:
P2110-BOOST PRESSURE SERVO MOTOR CIRCUIT SHORT CIRCUIT
When Monitored: With the ignition on.
Set Condition: The ECM detects a short to battery on the Boost Pressure Servo Motor
Control circuit.
POSSIBLE CAUSES
INTERMITTENT CONDITION
BOOST PRESSURE SERVO MOTOR
BOOST PRESSURE SERVO MOTOR CONTROL SHORT TO VOLTAGE
ENGINE CONTROL MODULE - INTERNAL
ENGINE CONTROL MODULE - INTERNAL SHORT TO VOLTAGE
TEST ACTION APPLICABILITY
1NOTE: If DTC P1611, P2306 or P2332 is present with this DTC, diagnose
DTCs P1611, P2306 or P2332 before diagnosing this DTC.
NOTE: If the ECM detects and stores a DTC, the ECM also stores the
engine/vehicle operating conditions under which the DTC was set. Some of
these conditions are displayed on the DRB at the same time the DTC is
displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to
duplicate these conditions may assist when checking for an active DTC.
Turn the ignition on.
With the DRB, erase ECM DTCs.
Test drive the vehicle and monitor the DRB for ECM DTCs.
Did this DTC set again?All
Ye s!Go To 2
No!Go To 5
164
DRIVEABILITY - DIESEL

Symptom List:
P2111-BOOST PRESSURE SERVO MOTOR CIRCUIT SHORT TO
GROUND
P2112-BOOST PRESSURE SERVO MOTOR CIRCUIT OPEN CIR-
CUIT
P2510-BOOST PRESSURE SERVO MOTOR SHORT TO GROUND
P2526-BOOST PRESSURE SERVO MOTOR OPEN CIRCUIT
P2526-BOOST PRESSURE SERVO MOTOR SHORT TO GROUND
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P2111-BOOST PRESSURE
SERVO MOTOR CIRCUIT SHORT TO GROUND.
When Monitored and Set Condition:
P2111-BOOST PRESSURE SERVO MOTOR CIRCUIT SHORT TO GROUND
When Monitored: With the ignition on.
Set Condition: The ECM detects a short to battery on the Boost Pressure Servo Motor
Control circuit.
P2112-BOOST PRESSURE SERVO MOTOR CIRCUIT OPEN CIRCUIT
When Monitored: With the ignition on.
Set Condition: The ECM detects an open or short to ground on the Boost Pressure Servo
Motor Control circuit.
POSSIBLE CAUSES
CHECKING THE ENGINE CONTROL RELAY SYSTEM
INTERMITTENT CONDITION
12 VOLT SUPPLY CIRCUIT OPEN
BOOST PRESSURE SERVO MOTOR CONTROL CIRCUIT SHORTED TO GROUND
BOOST PRESSURE SERVO MOTOR CONTROL CKT OPEN
BOOST PRESSURE SERVO MOTOR
ENGINE CONTROL MODULE
167
DRIVEABILITY - DIESEL