2020-2021 Blazers equipped with the 2.0L engine (RPO LSY) may have a humming or vibration sound coming from the front of the vehicle when driving at speeds over 50 mph (80 km/h). The sound may be caused by the aero shutters being closed at highway speeds. (Fig. 6)
Fig. 6
When the airflow traveling through the front fascia grille opening hits the closed shutter panels, the air behind the grille opening becomes turbulent. The buildup of or air turbulence causes the energy absorber foam to start vibrating and moving up and down, which may result in the foam making intermittent contact with the lower grille close-out panel and cause it to flutter.
When the panel flutters, it vibrates against the fascia, creating the humming sound. The sound may be heard in the passenger compartment when driving at highway speeds and, in some cases, a vibration may be felt through the shift knob or steering wheel.
If the humming condition is found, install a foam block between the back vertical wall of the grille lower close-out panel and the body center fascia support bracket. The foam block used for the repair can be cut from an existing GM left-side door foam protector block that is on every new vehicle delivery. (Fig. 7) The foam block is removed from the vehicle during PDI and should be retained for use in this repair procedure. The original foam block is large enough to complete approximately four repairs.
Fig. 7
The foam block has a depth of approximately 25 mm (1 inch) and a width of approximately 35 mm (1.4 inches). It should be trimmed to a height of 25 mm (1 inch).
Insert the foam block between the close-out panel rear vertical wall and the center fascia support bracket (Fig. 8) through the grille opening on the vehicle. It is not necessary to remove the front fascia in order to install the foam block.
Fig. 8
To install the foam block, reach one hand through the grille opening to pull back on the close-out panel rear vertical wall and use the other hand, or a tool such as 90-degree needle nose pliers, to insert the foam block.
Once installed, the foam block will create a preload to the grille close-out panel to prevent it from fluttering. (Fig. 9)
Fig. 9
For additional information, refer to Bulletin #21-NA-038.
– Thanks to Pamela Francisco
