P1668

DTC P1668

DTC Descriptor

DTC P1668
Generator L-Terminal Control Circuit

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection





Circuit/System Description
The engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn on the field circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect low voltage on generator turn on signal circuit voltage 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 generator turn on signal circuit. The ECM performs key ON and RUN tests to determine the status of the generator turn on signal circuit.

Conditions for Running the DTC
Key ON Test
^ No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.
^ The ignition is in RUN position.
^ The engine is not running.

RUN Test
^ No generator, CKP sensors, CMP sensor DTCs are set.
^ The engine is running.

Conditions for Setting the DTC
During the Key ON test the ECM detects a high signal voltage on the generator turn on signal circuit for at least 5 seconds. Or During the RUN test the ECM detects a low signal voltage on the generator turn on signal circuit for at least 15 seconds.

Action Taken When the DTC Sets
^ The ECM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped.
^ The ECM will not illuminate the malfunction indicator lamp (MIL).
^ The ECM will store conditions, which were present when the DTC set as Fail Records data only.

Conditions for Clearing the DTC
^ The ECM will command the message OFF after one trip in which the diagnostic test has been run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ Using the scan tool Clear DTC Information function can clear the DTC.

Reference Information

Schematic Reference
Starting and Charging Schematics

Connector End View Reference
Engine Electrical Connector End Views

Electrical Information Reference
^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

Scan Tool Reference
^ Scan Tool Data List
^ Scan Tool Data Definitions

Circuit/System Testing
1. With ignition ON, and the engine OFF.
2. Disconnect the generator harness and measure the voltage of the generator turn on signal circuit, should read near 0 volts.
^ If greater than 0 volts test the generator turn on signal circuit for a short to voltage, or replace the ECM.

3. With ignition ON, and the engine running, the voltage of the generator turn on signal circuit, should read near 5 volts.
^ If no voltage is measured, test the generator turn on signal circuit for a short to ground, an open or a high resistance or replace the ECM.
4. Go to Charging System Test.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for ECM replacement, setup, and programming