Troubleshooting - No Codes: Introduction

Before diagnosing symptoms or intermittent faults, perform steps in BASIC DIAGNOSTIC PROCEDURES and appropriate SELF-DIAGNOSTICS articles. Use this article to diagnose driveability problems existing when a hard trouble code is not present.

NOTE: Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

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

Use INTERMITTENT SIMULATION under TEST PROCEDURES to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Most intermittent faults are caused by faulty electrical connections or wiring. Perform careful inspection of suspect circuits for:

Poor mating of coupler halves, or terminals not fully seated in coupler body (backed out).
Terminals damaged or improperly formed. Reform coupler terminals in problem circuit to increase contact tension.
Poor terminal-to-wire connection.

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