Service Bulletin

Bulletin No.:

21-NA-038

Date:

April, 2022

TECHNICAL
Subject:

Humming Noise Heard Coming from Front End of Vehicle When Driving at Highway
Speeds
This bulletin replaces PIT5814. Please discard PIT5814.

Brand:

Model:

Chevrolet

Blazer

Model Year:

VIN:

from

to

from

to

2020

2022

SOP

3GNKBFRS5NS172574

Involved Region or Country

Engine:

Transmission:

LSY

All

North America

Additional Options (RPOs)
Note: Condition may be mistaken for a TCC shudder or a mis-diagnosis could include
coasting through in neutral with engine off (under safe conditions).
Condition

Some customers may comment on hearing a vibration or humming type noise coming
from the front end of the vehicle when they are driving at speeds of 80 KPH (50 MPH) or
higher. This noise could be mistaken for a transmission related noise or wheel bearing
noise.

Cause

The cause of the condition may be that. when driving at highway speeds, the aero
shutters are closed. Under this condition, air flow traveling through the front fascia grille
opening hits the closed shutter panels, starts to build up within this area behind grille
opening and becomes turbulent.
This buildup of air turbulence causes the Energy Absorber Foam to start vibrating,
moving up/down. This vibrating Energy Absorber Foam can make intermittent contact
with the lower grille close-out panel and cause the lower close-out panel to flutter. When
the lower close-out panel flutters, it vibrates against the fascia that is secured to. This
vibration creates the humming noise that can be heard from within the passenger
compartment when vehicle is driven under above mentioned conditions. In some cases,
the driver may also feel this vibration through the shift knob or steering wheel.

Correction

After verifying the condition, install a foam block between the back vertical wall of grille
lower close-out panel and the body center fascia support bracket, following the steps in
the service Procedure below.

Copyright 2022 General Motors LLC. All Rights Reserved.

Page 2

April, 2022

Bulletin No.: 21-NA-038

Service Procedure

5736488

Note: The foam block used for this repair will be cut
from an existing GM left side door foam protector block
(1) that arrives on every new vehicle delivery. 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 4 repairs.

5736490

Note: The location of the foam block is designated by
the arrow and the dashed box in the graphic above.
1. The foam piece is approximately 25 mm (1 inch)
thick and should be trimmed to a height (1) of 25
mm (1 inch), and already has a width (2) of 35 mm
(1.4 inches).

Bulletin No.: 21-NA-038

April, 2022

Page 3
2.2. With the other hand (or a tool such as 90–
degree needle nose pliers, to help assist)
insert the foam block between the close-out
panel rear vertical wall and the center fascia
support bracket.

5736495

Note: It is NOT necessary to remove the front fascia, in
order to install the foam block.
2. Reaching through the grille opening on the vehicle,
access the grille close-out panel rear vertical wall
and the center fascia support bracket.
2.1. Reach one hand through the front grille
opening to pull back on close-out panel rear
vertical wall.

5736497

2.3. This foam block will create a pre-load to the
grille close-out panel and prevent it from
vibrating/fluttering.
3. Road test the vehicle to ensure the condition has
been corrected.

5736494

Note: In the graphic above, the foam block is
purposely exposed to show the location where to insert
it between panel and body fascia support bracket.

Page 4

April, 2022

Bulletin No.: 21-NA-038

Parts Information
As noted above, the foam block should be retained
after removal from a vehicle during PDI.

Warranty Information
For vehicles repaired under the Bumper-to-Bumper
coverage (Canada Base Warranty coverage), use the
following labor operation. Reference the Applicable
Warranties section of Investigate Vehicle History (IVH)
for coverage information.
Labor Operation

Description

Labor Time

1086318*

Trim and Install Foam Block Between Grille Lower Close-out
Panel and the Center Fascia Support Bracket

0.5 hr

*This is a unique Labor Operation for Bulletin use only. Labor time has been included in the labor operation code to procure the
foam block from a new vehicle during the PDI process.

Additional SI Keywords
Vibration, shudder.
Version

2

Modified

Released February 17, 2021
Revised March 29, 2022 – Added Note to Correction, SI Key Words, 2022 Model Year
and VIN Break point.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a
job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

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