Bulletin No.:

Service Bulletin

Date:

20-NA-024
March, 2021

INFORMATION
Subject:

Information on Vehicle Slow to Heat Up in Cold Ambient Temperatures
Model Year:

Brand:

Buick

Chevrolet

Model:

VIN:

from

to

Encore

2013

2021

Encore GX

2020

2021

Cruze

2011

2015

Cruze
(VIN P)

2016

2016

Cruze (Gen II
- VIN B)

2016

2019

Sonic

2012

2020

Spark

2013

2020

Trax

2013

2021

Trailblazer

2021

2021

from

—

to

—

Engine:
1.2L, 1.3L,
1.4L or
1.8L Gas

Transmission:

L3T, LIH,
LLO, LUJ,
LUV, LE2,
2HO,
LUW, LWE

—

Involved Region or Country

North America

Condition

Some customers may comment in cold ambient temperatures on finding one or more of
the following conditions:
• The engine is slow to reach normal coolant operating temperatures as indicated by
the engine coolant temperature gauge.
• The air coming out of the heater outlet ducts is not warm enough for their personal
preferences.
• The vehicle is not warm when using the Remote Vehicle Start feature.

Cause

This condition may be caused by the energy efficient engines that these vehicles are
equipped with. These engines may not generate the same amount of heat at idle that the
customer may be accustomed to when compared to older less efficient engines.
Additionally, depending on extreme cold ambient temperatures, a short drive cycle under
light engine load may also not generate enough heat to reach normal engine coolant
operating temperatures as indicated by the engine coolant temperature gauge and
therefore insufficient heat from the heater outlet ducts.

Information

1. Perform the Diagnostic System Check - Vehicle.
• If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle in SI.
• If no DTCs are set, go to Step 2.
2. Verify the coolant in the radiator surge tank is at the correct level.
3. For vehicles with manual heater control or automatic control in manual mode,
instruct the customer that during extreme cold ambient temperatures to place the
blower on medium (3) instead of high (6) during vehicle warm-up or remote start.
Note: Automatic HVAC operated in Auto mode is already optimized for lower blower
speed during engine warm-up.
– This will result in warmer outlet temperatures sooner. When the blower is
operated on high speed (6) with extreme low ambient temperatures, the heater
core will pull more heat out of the coolant than the engine can produce at idle or
low speed causing the engine and outlet temperature to be slower to warm up.
4. For Encore and Trax ONLY: Installing a Winter Grille Cover will help retain some
engine heat.

Copyright 2021 General Motors LLC. All Rights Reserved.

Page 2

March, 2021

Bulletin No.: 20-NA-024

Note: Understand that heater benefit will be small using the Winter Grille Cover.

⇒ Refer to Service Bulletin Numbers 16-NA-405 (LUV) or 17-NA-221 (LE2) for
more information.
5. DO NOT replace the engine coolant thermostat unless a DTC is set related to the
thermostat, as the ECM monitors the thermostat each key cycle to ensure it is
operating within design parameters. ⇒ If there are no DTCs, the engine coolant level
is correct, and the thermostat is diagnosed as operating correctly, then the comment
of the engine is slow to reach normal coolant operating temperatures should be
considered as a normal operating condition of these energy efficient engines in cold
ambient temperatures.
During a long descent or steep downhill grade, the engine may be in DFCO (Deceleration
Fuel Cut Off) mode, which will not produce additional heat. However in other driving
situations, placing the engine in Manual Mode will slightly increase engine heat. To do
this, place the shifter in “L" or “M", then use +/- on the shifter to perform a light engine
brake to keep RPMs up above idle speeds.
Customer Information

Please communicate to the customer that this condition as described is a normal
operating characteristic of their vehicle. It will not impact the designed performance or
reliability of the vehicle. Please share this information with the customer, including a copy
of this bulletin.

Parts Information
No parts are required for this repair.
Version

4

Modified

Released January 30, 2020
February 11, 2020 – Removed previous step #4 (long descent or steep grade) from the
Information section and added information at the end of the Information section.
February 12, 2021 – Added the Encore GX and Trailblazer Models, added the 2021
Model Year to Encore and updated the bulletin references in Step 4.
March 16, 2021 – Added Engine RPOs L3T and LIH.

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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