P1668
DTC P1668
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 Descriptor
DTC P1668
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Generator L-Terminal Control Circuit
Diagnostic Fault Information
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 generator 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 generator turn ON signal circuit. The ECM performs tests to determine the status of the generator 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 generator turn on signal circuit for at least 5 seconds.
* During the RUN test, the ECM detects low voltage on the generator 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 [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views A/C Compressor Clutch
Description and Operation
Charging System Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References 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 generator turn on signal circuit and ground.
• If greater than the specified value, test the generator 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 generator turn on signal and ground.
• If less than the specified value, test the generator 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 Verification Tests after completing the diagnostic procedure.
* Control Module References Control Module References for ECM replacement, setup, and programming
* Generator Replacement Service and Repair