Engine Controls - Tests W/O Codes: Introduction

Before attempting to diagnose symptoms or intermittent faults, ensure steps in the BASIC TESTING and also in the appropriate TESTS W/CODES articles have been performed. Use this article to diagnose driveability problems that exist when a hard fault code is not present.

Symptom checks are intended to direct the technician to malfunctioning component(s) so that further diagnosis may be performed. A "symptom" should lead to further testing of specific components or systems, or verification of adjustment specifications.

Use intermittent test procedures to locate intermittent driveability problems that do not occur when the vehicle is being tested. These problems may cause a noticeable driveability problem or cause the "malfunction" warning light to illuminate on some vehicles.

It is also possible that certain driveability concerns have been rectified by the manufacturer through substitution of a revised calibration chip or computer control unit. Check with manufacturer for latest information on updated chips and control units.