Engine Controls - System & Component Testing - 4.0L & 4.6L: Introduction
Before testing separate components or systems, perform BASIC DIAGNOSTIC PROCEDURES article. Since many computer-controlled and monitored components will cause a Diagnostic Trouble Code (DTC) to set if they malfunction, also perform SELF-DIAGNOSTICS in SELF-DIAGNOSTICS - 4.0L & 4.6L article.
NOTE:
Testing individual components does not isolate short or open circuits. Perform all resistance and voltage tests using 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.