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, or L-terminal 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

* During the Key ON test the ECM detects high voltage on the generator turn on signal circuit for 5 seconds.
* With the engine running the ECM detects 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 to be illuminated on the instrument panel cluster (IPC).
* 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 history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

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 terminal 1 and ground.

^ If greater than the specified range, 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 circuit and ground.

^ If less than the specified range, test the generator turn on signal circuit for a short to ground, an open or a high resistance. If the circuit tests normal, replace the ECM.

4. If the circuit tests normal, replace the generator.

Repair Instructions

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

* Generator Replacement (With 4.2L Engine) Generator Replacement (With V8 Engine)