Engine Controls - Basic Diagnostic Procedures: Introduction

NOTE: Vehicles are equipped with an engine immobilizer system. Engine immobilizer system is a theft deterrent system which disables engine from starting by not allowing ignition system and fuel injector operation unless ignition key identification code matches identification code stored in Engine Control Module (ECM). For additional information on system operation and testing, see appropriate ENGINE IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT.

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition. First step in diagnosing any driveability problem is verifying customer's complaint with a test drive under conditions problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning computerized system, perform each test listed in this article.

NOTE: Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.