Engine Controls - System & Component Testing - 3.9L: Introduction

Before testing individual components or systems, perform procedures in BASIC TESTING - 3.9L article. Since many computer controlled and monitored components set a fault message if they malfunction, also perform procedures in SELF-DIAGNOSTICS - JEEP, TRUCKS & RWD VANS article.

NOTE: Testing of individual components does not isolate possible shorts or opens in wiring harness of electronically controlled systems. Perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance unless otherwise instructed in procedure. Use an ohmmeter to isolate wiring harness shorts or opens.