For 1990-2009 cars

# Info - Excessive Fuel Cap Replacement

Subject: | Diagnostic Information For The Evaporative Emission (EVAP) Control System

Models: | 1998-99 Buick LeSabre, Park Avenue and Riviera

| 1998-99 Cadillac Eldorado, Seville and DeVille

| 1998-99 Oldsmobile Aurora, Regency, Eighty-Eight and LSS

| 1998-99 Pontiac Bonneville and SSE

This bulletin is being issued to provide information to accurately diagnose an evaporative fuel emission system condition.

The Evaporative Emission (EVAP) Control System is required on the vehicles listed above to detect evaporative fuel emission system leaks as small as 1.0 mm (0.040 in).

If the system senses a leak, the Malfunction Indicator Lamp (MIL) may illuminate and/or Diagnostic Trouble Codes (DTCs) P0440 EVAP System (Large Leak) or P0442 EVAP Control System Small Leak Detected may be set.

If an EVAP DTC is set, it is important to determine whether it is a current code or a history code. Do not replace parts if a history EVAP DTC code is set. Clear the history EVAP DTC code and proceed using standard diagnostic procedures.

In order to diagnose a system condition accurately, the appropriate diagnostic tables and aids in the applicable Service Manuals must be used. It is important to follow the procedures and the operating criteria listed in the Diagnostic Trouble Code (DTC) Tables.

Also, it is important to use the required tools listed in the Service Manuals. Special tools such as the J 41413 EVAP Pressure/Purge Diagnostic Station for a clean, dry, low pressure gas source and the J 41416 Ultrasonic Leak Detector are needed in order to avoid unnecessary component replacement.

Components such as fuel caps, tank pressure sensors, canister vent solenoids and fuel filler pipes are being unnecessarily replaced until the condition is corrected. The majority of these parts returned for warranty have been diagnosed in Engineering as "No Trouble Found (NTF)".

As part of our continuing effort to reduce customer returns and "No Trouble Found(s)", it is essential that accurate diagnosis be made and verification of the repair be accomplished. If a condition is attributed to the fuel cap not being tightened properly, ensure the customer is provided instruction on the appropriate tightness of the fuel cap. This will ensure a high level of customer satisfaction.