Engine Controls - Tests W/O Codes: Introduction

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

A symptom can be defined as an indication or characteristic of a condition which causes a driveability complaint. Often a customer's complaint of a driveability symptom will be any condition which is different from when the car was purchased or new. Always understand the customer's perception of the symptom. Symptom checks are intended to direct the technician to malfunctioning component or system so that further diagnosis may be performed. A symptom should lead to further testing of specific components or systems, or verification of adjustment specifications.

An intermittent driveability problem can be defined as one that comes and goes during any particular driving cycle. This type of problem includes electrical circuits or component problems that may or may not set a soft code in the ECA memory. This means the problem may turn the CHECK ENGINE or SERVICE ENGINE SOON light on or cause it to flicker without setting a code in memory. The intermittent problem could occur in a circuit not monitored by diagnostics. The key word in this definition is INTERMITTENT. If the problem is happening all the time, treat it as a symptom, not as an intermittent.