Engine Controls - Trouble Shooting - No Codes: Introduction

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

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

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

Use intermittent 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.

Always personally verify customer complaint. Always verify that complaint is truly a system malfunction. Perform a quick test to determine if the vehicle systems have logged fault codes. Call up the faulted system or appropriate test schedule to verify the correct control module is installed in the car. Follow Diagnostic Information System (DIS or MoDiC) on screen instructions and perform all tests as specified. Use DIS/MoDiC and fault symptom diagnostic procedures as necessary. Follow appropriate test module procedures for systems that malfunction but fail to set faults in memory.

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