P1668

DTC P1668

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC P1668
- 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

The engine is running.


Conditions for Setting the DTC

With the engine running the ECM detects a low voltage on the generator turn ON signal circuit for 15 seconds.


Action Taken When the DTC Sets

* The ECM will command the charge indicator and warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC).
* 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

A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.


Reference Information
Schematic Reference

Starting and Charging Schematics (Starting and Charging Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)



Circuit/System Testing

1. Ignition ON, engine OFF. Disconnect the generator harness connector.
2. Measure the voltage of the generator turn on signal circuit terminal 1. Verify the circuit has less than 1 volt.

• If greater than the specified value, test the generator turn on signal circuit for a short to voltage, or replace the ECM.

3. Engine running. Measure the voltage of the generator turn on signal circuit terminal 1. Verify the circuit has greater than 3.5 volts.

• If less than 3.5 volts, test the generator turn on signal circuit for a short to ground, an open or a high resistance, or replace the ECM.

4. Refer to Charging System Test (Charging System Test) .



Repair Instructions

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


Control Module References (Programming and Relearning) for ECM replacement, setup, and programming