PRE-RELEASE
DTC P0625 or P0626
| DTC P0625 or P0626 |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| DTC Descriptors |
DTC P0625
Generator F-Terminal Circuit Low Voltage
DTC P0626
Generator F-Terminal Circuit High Voltage
| Diagnostic Fault Information |
| Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
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B+
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P0625
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P0625
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-
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-
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Signal
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P0625
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P0625
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P0626
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-
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Control
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P0621
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P0621
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P0621
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-
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| Circuit/System Description |
The engine control module (ECM) uses the generator field duty cycle signal circuit, or F-terminal circuit, to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to high side of the field windings in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of the generator field duty cycle signal circuit. When the ignition is ON and the engine is OFF, the ECM should detect a duty cycle near 0%. When the engine is running, the duty cycle should be between 5-99%.
| Conditions for Running the DTC |
P0625
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The engine is running.
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The engine speed is less than 3 000 RPM.
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P0626
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The engine is not running.
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The ignition is in the ON position.
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| Conditions for Setting the DTC |
P0625
The ECM detects a pulse width modulated (PWM) signal less than 5% for 15 s.P0626
The ECM detects a pulse width modulated (PWM) signal greater than 65% for 15 s.| Action Taken When the DTC Sets |
DTC P0625 and P0626 are C type DTCs.
| Conditions for Clearing the DTC |
DTC P0625 and P0626 are C type DTCs.
| Reference Information |
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Charging System Description and Operation
Electrical Information Reference
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Circuit Testing
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Connector Repairs
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Testing for Intermittent Conditions and Poor Connections
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Wiring Repairs
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DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
| Circuit/System Verification |
Engine running, observe the scan tool Generator F-Terminal Signal Circuit parameter. The Generator F-Terminal Signal Circuit parameter should display between 5-99%.
| Circuit/System Testing |
| 1. |
Verify that a test lamp illuminates between the G13 Generator B+ terminal A X1 and ground.
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| 2. |
If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
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| 3. |
Ignition OFF, disconnect the X2 harness connector at the G13 Generator.
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| 4. |
Ignition ON, verify the scan tool Generator F-Terminal Signal parameter displays less than 5%.
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| 5. |
If greater than the specified range, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.
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| 6. |
Install a 3 A fused jumper wire between B+ and the signal circuit terminal 2.
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| 7. |
Verify the scan tool Generator F-Terminal Signal parameter displays greater than 95%.
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| 8. |
If less than the specified range, test the signal circuit terminal 2 for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.
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| 9. |
If the circuit tests normal replace the G13 Generator.
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| Repair Instructions |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
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Refer to
Generator Replacement (Diesel)
Generator Replacement (LAU/A28NER)
Generator Replacement (LLU/A16LET)
Generator Replacement (LHU/A20NFT)
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Control Module References
for ECM replacement, setup, and programming
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