Troubleshooting - No Codes: Introduction

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.

Before diagnosing symptoms or intermittent faults, perform basic diagnostic procedures in appropriate BASIC DIAGNOSTIC PROCEDURES article and applicable self-diagnostic tests in appropriate SELF-DIAGNOSTICS article. Use this article to diagnose driveability problems existing when a hard Diagnostic Trouble Code (DTC) is not present.

NOTE: Some driveability problems may have been corrected by manufacturer with a revised Powertrain Control Module (PCM). Check with manufacturer for latest PCM application.

Symptom checks direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, system test or adjustment.

Use intermittent test procedures to locate 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. These test procedures should also be used if a soft (intermittent) trouble code is present, but no problem is found during self-diagnostic testing.

NOTE: For specific testing procedures, see appropriate SYSTEM & COMPONENT TESTING article. For specifications, see appropriate ON-VEHICLE ADJUSTMENTS and SERVICE & ADJUSTMENT SPECIFICATIONS articles.