Engine Controls - Basic Testing: Introduction

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

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the 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, plugged or misrouted vacuum hoses. Before condemning the 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.