Engine Controls - System & Component Testing: Introduction

Before testing separate components or systems, perform procedures in BASIC DIAGNOSTIC PROCEDURES article. Since many computer-controlled and monitored components set a diagnostic trouble code if they malfunction, also perform procedures in SELF-DIAGNOSTICS - GX470 article.

It is possible there is an open or short in MIL wire harness or malfunction inside ECM itself which will cause MIL to blink. Diagnose TC terminal circuit in this case. See TC TERMINAL CIRCUIT under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - GX470. If MIL remains on or will not illuminate, see MIL CIRCUIT under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - GX470.

If no Diagnostic Trouble Codes (DTC) are present and a driveability condition exists, see TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

NOTE: Testing individual components does not isolate short or open circuits. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate shorted or open wiring harness.