Engine Controls - Basic Diagnostic Procedures - CNG: Introduction

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See appropriate COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.

CAUTION: Always perform fuel system purge before servicing or removing fuel system components. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEMS. See SERVICE PRECAUTIONS .

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

Before proceeding with basic diagnostic 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 Powertrain Control Module (PCM). See DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - RAN VAN article.

If no-start condition still exists after checking and repairing all DTCs, perform a careful and complete visual inspection. See PRELIMINARY INSPECTION & ADJUSTMENTS . 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.