Engine Controls - Tests W/Codes - 4.0L: Introduction

NOTE: For Grand Cherokee with 5.2L engine, see TESTS W/CODES - 5.2L article in the ENGINE PERFORMANCE section.

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with self-diagnostics. If no Diagnostic Trouble Codes (DTCs) or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE section for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).