Engine Controls - Trouble Shooting - No Codes: Introduction

Before diagnosing symptoms or intermittent faults, follow proper workflow. See TESTING PROCEDURE under SELF-DIAGNOSTICS - EXCEPT 7-SERIES or SELF-DIAGNOSTICS - 7 SERIES article. If no Diagnostic Trouble Codes (DTCs) are present and a no start condition exists, proceed to BASIC DIAGNOSTIC PROCEDURES article. If no DTCs are present and a driveability condition exists, diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

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.

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.