21NA237

Bulletin No.:
Service Bulletin
Date:
21-NA-237
November, 2021
TECHNICAL
Subject:
Poor Heater Performance On Drivers Side
Attention: This bulletin does not apply to vehicles with the L5P engines.
This bulletin replaces PIT5818. Please discard PIT5818.
Model Year:
Brand:
Model:
Cadillac
Escalade
Models
2021
Chevrolet
Silverado
1500 (New
Model)
2019
Chevrolet
Silverado
2020
Chevrolet
Suburban
2021
Chevrolet
Tahoe
2021
GMC
Sierra 1500
(New Model)
2019
GMC
Sierra
2020
GMC
Yukon
Models
2021
from
VIN:
Engine:
Transmission:
to
2021
Involved Region or Country
North America, Europe, Russia, Middle East
Condition
Some customers may comment on lower heater performance from the driver side HVAC
vents when compared to the passenger side.
• In some cases, the driver side center dash vent will have the lowest temperature.
Cause
This may be caused by a blocked heater core tube.
Correction
Flush the cooling system using a flushing agent recommended by GM.
Note: GM of Canada is working on making this product available from other sources but
as of the time of publication, the source in Canada will be Canadian Tire under part
number 038–0891.
⇒ Perform a flushing procedure using Blue Devil Radiator Flush Cooling
System Cleaner, which is approved by GM engineering.
Copyright 2021 General Motors LLC. All Rights Reserved.
Page 2
November, 2021
Service Procedure
Important: All signs of the cooling system cleaner
must be flushed completely from the cooling system
before adding the coolant.
Refer to Cooling System Draining and Filling and
Flushing in SI.
Note: The temperature difference between the vents
when the process is complete should no more than 5-7
degrees C with the engine at full operating temperature
with all vents open. If the temperature difference
persists after flushing, the dealer should contact TAC.
1. Drain coolant and wash all of the coolant out of the
system with clean drinkable water.
2. Add flushing chemical (one container) to the surge
tank and fill the cooling system with clean drinkable
water.
Note: Do not allow the vehicle to become exposed to
sub-freezing temperatures with the engine off, the
flushing chemical provides no freeze protection.
3. Allow the engine to idle for 4 hours, the vehicle can
also be driven if desired during this period.
4. Confirm that the heater outlet temperatures are
within 5-7 degrees C with all vents open and the
heater on high fan with outside air.
5. Drain and wash the cooling system with clean
drinkable water and refill with a 50/50 mix of
Dexcool Coolant and clean drinkable water.
Bulletin No.: 21-NA-237
The performance of the heater may improve very soon
after the flushing chemical is placed in the system. The
chemical must remain in the system for between 3 and
4 hours to have the effect of removing the deposit that
is causing the heater core to be blocked. This material
is primarily in the radiator, so if it is not thoroughly
cleaned out, the condition could recur.
Parts Information
Causal
Part
Description
N/A
DEX-COOL®
Part
Number
Refer
to EPC
Qty
As Required
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
4088258*
Cooling System Complete Flush
4.0 hr
*This is a unique Labor Operation for Bulletin use only.
Version
1
Modified
Released November 18, 2021
ADDITIONAL SI KEYWORDS:
cold, cool, heat, hot,
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.
WE SUPPORT VOLUNTARY
TECHNICIAN
CERTIFICATION