Engine Controls - Basic Diagnostic Procedures: Introduction

NOTE: Vehicles are equipped with an OBD-II diagnostic system. For thorough and complete diagnosis, manufacturer strongly recommends the purchase of BMW-specific diagnostic equipment. For diagnosis, see 2002 SELF-DIAGNOSTICS , 2003 SELF-DIAGNOSTICS - Except 7-Series or 2003 SELF DIAGNOSTICS - 7-Series article.

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition. The first step in diagnosing any driveability problem is verifying the problem with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control 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.