Engine Controls - Basic Diagnostic Procedures - V6 & V8: Introduction

NOTE: Before performing basic diagnostic procedures, check for any related Technical Service Bulletins (TSBs).

NOTE: On Avalon, Camry, Camry Solara, Highlander, Land Cruiser, Sequoia, Sienna and 4Runner, an engine immobilizer system may be used. 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 Engine Control Module (ECM). Models equipped with engine immobilizer system may be identified by looking at the ignition key. On models equipped with engine immobilizer system the top of the ignition key is thicker than a standard ignition key, as a transponder chip is incorporated into the top of the ignition key. For additional information on system operation and testing, see appropriate ENGINE IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT.

NOTE: When battery is disconnected on Sienna, power sliding doors will need to be initialized. See SLIDING DOOR INITIALIZATION PROCEDURE (SIENNA) in COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. When battery is disconnected on Celica, power moon roof may need to be initialized for proper operation. See SUN ROOF INITIALIZATION (CELICA) in COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION.

Before proceeding with basic diagnostic service procedures, ensure testing procedure is followed, as some systems which may result in a no-start condition may cause a Diagnostic Trouble Codes (DTC) to be stored in the Engine Control Module (ECM). See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.

Once technician has checked for any stored DTCs, perform a careful and complete visual inspection. Many problems result from mechanical breakdowns, poor electrical connections or damaged/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.