Engine Controls - Tests W/O Codes: Introduction

Before diagnosing symptoms or intermittent faults, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in TESTS W/CODES article. Use this article to diagnose driveability problems when a current trouble 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 Indicator Light (MIL) to illuminate on some vehicles.

It is also possible that certain driveability concerns have been rectified by the manufacturer through substitution of a revised PROM or Powertrain Control Module (PCM). Check with manufacturer for latest information on updated PROMs and PCMs.