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When Monitored:
Ignition on.
Set Condition:
Low voltage detected at the WIF signal circuit at the ECM.
Possible Causes
OTHER DTC’S PRESENT
WATER IN FUEL
ECM
INTERMITTENT CONDITION
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.OTHER DTC’S PRESENT
With the scan tool, read DTCs.
Do you have any additional water in fuel DTC’s?
Ye s>>
Repair other Water in fuel sensor DTC’s first.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 2
2.WAT E R I N F U E L
Using the service publications as a guide, drain the water in fuel separator.
Did the DTC become inactive after draining the water in fuel separator?
Ye s>>
Clear DTC, repair complete.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 3
3.ECM
Disconnect the WIF sensor harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Using the scan tool, monitor for DTC’s while connecting a jumper wire
between the (G123) signal circuit of the water in fuel sensor and battery
voltage.
Did the water in fuel light go out?
Ye s>>
Refer to the INTERMITTENT CONDITION Symptom (Diag-
nostic Procedure). (Refer to 9 - ENGINE - DIAGNOSIS
AND TESTING)
No>>
Replace and program the ECM in accordance with the Ser-
vice Information.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
Page 858 of 5267
P2502-CHARGING SYSTEM ERROR
For a complete wiring diagramRefer to Section 8W.
Page 859 of 5267

When Monitored:
While the engine is running.
Set Condition:
The ECM cycles the voltage regulator in the generator while monitoring fora change in output voltage. If the
voltage does not drop when the regulator is off, the fault is set.
Possible Causes
DIRTY OR LOOSE CONNECTIONS
HIGH RESISTANCE IN THE B+ CIRCUIT
HIGH RESISTANCE IN THE B+ CROSS OVER CABLE
HIGH RESISTANCE IN THE GROUND CIRCUIT
GENERATOR
ECM
INTERMITTENT CONDITION
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.DIRTY OR LOOSE CONNECTIONS
Visually inspect the positive and negative connections at the battery.
Visually inspect the battery negative connections at the engine block.
Are the connections free of corrosion and are they tight?
Ye s>>
Go To 2
No>>
Clean and/or tighten the connections.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
2.HIGH RESISTANCE IN THE B+ CIRCUIT
Measure the voltage between the B+ post of the generator and the B+ post of the battery while the engine is run-
ning.
Is the voltage above .4 volts?
Ye s>>
Repair the high resistance in the B+ circuit from battery to the generator.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 3
3.HIGH RESISTANCE IN THE B+ CROSS OVER CABLE
Measure the voltage between the B+ post of the generator and the B+ post of the right side battery to the left side
battery while the engine is running.
Is the voltage above .4 volts?
Ye s>>
Repair the high resistance in the B+ cross over cable from right side battery to left side battery.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 4
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4.HIGH RESISTANCE IN THE GROUND CIRCUIT
Measure the voltage between the generator case and the B- post of the battery.
Is the voltage above .1 volts?
Ye s>>
Repair the high resistance in the ground circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 5
5.GENERATOR
Disconnect the Generator field harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance between the generator field terminals.
Is the resistance between .5 and 15 Ohms?
Ye s>>
Go To 6
No>>
Replace the generator.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
6.All
Turn the ignition off.
Reconnect the Generator field harness connector.
Disconnect the ECM harness connectors.
NOTE: Check connectors - Clean/repair as necessary.
Ignition on, engine not running.
Measure and record the voltage between battery positive circuits of the
ECM harness connector and the battery negative circuits of the ECM
harness connector.
Turn the ignition off.
Reconnect the ECM harness connectors.
Start the engine.
Use the scan tool to measure and record battery voltage.
Compare the voltage reading from the voltmeter with that of the scan
tool.
Are the readings within 3 volts of each other?
Ye s>>
Te s t C o m p l e t e .
No>>
Replace and program the ECM in accordance with the Service Information.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
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P2503-CHARGING SYSTEM OUTPUT LOW
For a complete wiring diagramRefer to Section 8W.
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When Monitored:
While the engine is running.
Set Condition:
The battery voltage exceeds target voltage by more than a calibrated value.
Possible Causes
OTHER DTC’S PRESENT
GENERATOR
FIELD DRIVER CIRCUIT SHORTED TO GROUND
ECM
INTERMITTENT CONDITION
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.OTHER DTC’S PRESENT
With the scan tool, read DTCs.
Is DTC P2502 set?
Ye s>>
Repair other DTC’s first.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 2
2.GENERATOR
Disconnect the Generator field harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance between the generator field terminals at the
generator.
Is the resistance between .5 and 15 Ohms?
Ye s>>
Go To 3
No>>
Replace the generator.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
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3.FIELD DRIVER CIRCUIT SHORTED TO GROUND
Disconnect the ECM harness connectors.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance of the generator field driver circuit between the
generator and battery negative.
Is the resistance greater than 100 ohms?
Ye s>>
Go To 4
No>>
Repair the generator field driver circuit shorted to ground.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
4.ECM
Measure and record the voltage between battery positive circuit of the
ECM harness connector and the battery negative circuits of the ECM
harness connector.
Reconnect the ECM connectors.
Use the scan tool to measure and record battery voltage.
Compare the voltage reading from the voltmeter with that of the scan
tool.
Are the readings within 3 volts of each other?
Ye s>>
Refer to the INTERMITTENT CONDITION Symptom (Diag-
nostic Procedure). (Refer to 9 - ENGINE - DIAGNOSIS
AND TESTING)
No>>
Replace and program the ECM in accordance with the Ser-
vice Information.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
Page 864 of 5267
P2504-CHARGING SYSTEM OUTPUT HIGH
For a complete wiring diagramRefer to Section 8W.