P1668

DTC P1668

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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
- 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.

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 after completing the diagnostic procedure. Verification Tests