Service Information Regarding a Pop/Clunk Noise From Rear of Vehicle on Initial Cold Start and/or During Warm-Up Drive Cycle (Inform Customer of Normal EVAP Vent Solenoid Operation)

This bulletin is being revised to remove the Equinox and Torrent Models and add the 2007 model year. Please discard Corporate Bulletin Number 04-06-05-009B (Section 06 -- Engine/Propulsion System).

The purpose of this bulletin is to provide service information regarding a normal characteristic of the evaporative emissions (EVAP) control system On-Board Diagnostic (OBD) testing. Some customers may comment that they hear a pop/clunk noise similar to a backfire type noise from the rear of the vehicle during initial cold start and/or during engine warm-up.

The noise may be generated from the EVAP vent solenoid opening and closing during the OBD test. The engine control module (ECM) or powertrain control module (PCM) performs the EVAP OBD test each ignition cycle the test parameters are met. For test parameters, refer to "EVAP System Diagnostics" or "Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure" in the appropriate Service Manual or SI.

Important: To help confirm that the EVAP vent solenoid is the noise the customer is hearing, the service technician should have the customer sit in the vehicle and listen to the EVAP vent solenoid being cycled using the TECH  2®. This operation can be found in the Powertrain/Special Function section of the TECH  2® menu.

If the noise from the customer comment was from the EVAP vent solenoid, no service is required. Replacing the vent solenoid will not change the normal sound of the required EVAP vent solenoid test.

If the noise from the customer comment was not from the EVAP vent solenoid, the technician should continue diagnosing the customer's concern.