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DTC P1668

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P1668 : Alternator L-Terminal Control Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Alternator L- Terminal

P1668

P1668

P1668

-

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 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 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 tests to determine the status of the alternator turn ON signal circuit.

Conditions for Running the DTC
    • No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.
    • The ignition ON, engine OFF for the ignition on test.
    • The engine running for the run test.

Conditions for Setting the DTC
    • During the ignition ON test, the ECM detects high voltage on the alternator turn on signal circuit for at least 5 seconds.
    • During the RUN test, the ECM detects low voltage on the alternator turn on signal circuit for at least 15 seconds.

Action Taken When the DTC Sets

DTC P1668 is a C type DTC.

Conditions for Clearing the DTC

DTC P1668 is a C type DTC.

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

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the generator.
  2. Ignition ON, test for less than 1 volt between the alternator turn on signal circuit and ground.
    3. ⇒If greater than the specified value, test the alternator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. Engine Running, test for greater than 3.5 volts between the alternator turn on signal and ground.
    4. ⇒If less than the specified value, test the alternator turn on signal circuit for a short to ground, an open/ high resistance. If the circuit tests normal, replace the ECM.
  4. If the circuit tests normal, test or replace the generator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    • Control Module References for ECM replacement, setup, and programming
    •  Generator Replacement : LNQ → LF1 → LE5
   


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