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DTC P1678

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 P1678: Immobilizer System - Incorrect Engine Control Module (ECM) Identification

Circuit/System Description

When the engine control module (ECM) are programmed and configured during installation, the ECM learns a specific immobilizer identifier which is unique to the vehicle. The immobiliser identifier is used to prevent swapping modules between vehicles. The body control module (BCM) is the keeper of the immobiliser identifier. During vehicle operation, the ECM compare his immobilizer identifier to the BCM. If the identifiers match, vehicle starting is allowed. If the immobilizer identifier does not match, vehicle starting is disabled.

Conditions for Running the DTC

Ignition is in the ACCESSORY or RUN position.

Conditions for Setting the DTC

An incorrect immobilizer identifier is received by the ECM.

Action Taken When the DTC Sets

    • The security indicator in the instrument cluster will illuminate.
    • Vehicle starting will be disabled.

Conditions for Clearing the DTC

A current DTC will be cleared when the ECM learns an immobilizer identifier.

Reference Information

Schematic Reference

Immobiliser Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Immobiliser Description and Operation

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Perform the Programming and Setup procedure for the ECM. Verify the DTC does not reset after programming.

If the DTC resets, replace the K20 Engine Control Module (ECM).

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup, and programming

   


© Copyright Chevrolet. All rights reserved
   


© Copyright Chevrolet. All rights reserved