P1668

DTC P1668, P2500, or P2501

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category

DTC Descriptors

DTC P1668

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Generator L-Terminal Control Circuit

DTC P2500

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Generator L-Terminal Circuit Low Voltage

DTC P2501

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Generator L-Terminal Circuit High Voltage

Diagnostic Fault Information






Circuit/System Description

The engine control module (ECM) uses the alternator turn ON signal circuit to control the load of the alternator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the alternator turn ON signal circuit. The ECM should detect low voltage on alternator turn on signal circuit when the ignition is ON and the engine is OFF or when the charging system malfunctions. With the engine running, the ECM should detect high voltage on the alternator turn on signal circuit. The ECM performs key ON and RUN tests to determine the status of the alternator turn on signal circuit.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

With the engine running, the ECM detects low/high compared to a predetermined voltage on the alternator turn on signal circuit for at least 15 seconds.

Action Taken when the DTC Sets

DTCs P1668, P2500 or P2501 are type C store only DTCs.

Conditions for Clearing the MIL/DTC

DTCs P1668, P2500 or P2501 are type C store only DTCs.

Reference Information

Schematic Reference

Starting and Charging Schematics Electrical Diagrams

Connector End View Reference

Component Connector End Views Fuel Pump and Level Sensor Assembly

Electrical Information Reference

* Circuit Testing Circuit Testing

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Testing

1. With ignition ON and the engine OFF, disconnect the alternator harness at the alternator and measure the voltage of the alternator turn on signal circuit terminal 1 X1 should read near 0 V.

• If greater than 0 V test the alternator turn on signal circuit for a short to voltage. If circuit test normal replace the ECM.

2. With ignition ON and the engine running, the voltage of the alternator turn on signal circuit terminal 1 X1 should read over 3.5 V.

• If no voltage is measured, test the alternator turn on signal circuit for a short to ground an open/high resistance If circuit tests normal replace the ECM.

3. If all circuits test normal, refer to Charging System Test Testing and Inspection.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

Control Module References Control Module References for module replacement, setup, and programming