Engine Controls - Basic Testing: Introduction

NOTE: This article contains general information on Basic Diagnostic Procedures on GM vehicles. The information in this article should not be used for a specific vehicle application.

The following diagnostic steps can help prevent overlooking simple problems. This is also the place to start diagnosis for a "NO-START" condition.

The first step in diagnosing any driveability problem is to verify the problem exists. This may be accomplished by test driving the vehicle under the conditions during which the problem reportedly occurs.

Prior to entering self-diagnostics, a careful and complete inspection of several systems is required. Most driveability or "no-start" problems are not related to computerized engine control systems, but are usually simple mechanical, electrical, fuel or vacuum problems. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged or misrouted vacuum hoses.

Before considering the computer system as a possible cause of problems, check ignition high tension wires, fuel supply, electrical connections and vacuum hoses. Failure to check these can result in improper diagnosis or lost diagnostic time.

NOTE: All voltage tests should be performed with a Digital Volt- Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in testing procedures.