Poor Heater Performance On Drivers Side – 2019-2021 Cadillac Chevrolet GMC

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Bulletin No.: PIT5868
Published date: 11/29/2021
Preliminary Information
PIT5868 Poor Heater Performance On Drivers Side
Models
Brand: Model: Model Years:
VIN:
Engine: Transmissions:
from to
Cadillac Escalade Models 2021 All All All All
Chevrolet Silverado 1500 (New Model) 2019 All All All All
Chevrolet Silverado 2020 – 2021 All All All All
Chevrolet Suburban 2021 All All All All
Chevrolet Tahoe 2021 All All All All
GMC Sierra 1500 (New Model) 2019 All All All All
GMC Sierra 2020 – 2021 All All All All
GMC Yukon Models 2021 All All All All
Involved Region or Country North America
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
The cause of this condition could be one of the following:
Cause 1: The heater core may have become plugged. When the heater core begins
to plug, it affects the driver side center vent first.
Cause 2: Both single and dual zone HVAC cases utilize two temperature doors per
side (a total of four doors), shown below. In the photo below, call-out 1 shows the
passenger side temperature doors and heater core. Call-out 2 show the driver side
temperature doors and heater core. Call-out 4 shows the evaporator air
temperature sensor location in relation to the driver side temperature door which
will be helpful later in this document. Inside the HVAC case, there are four white
links which connect each of the four temperature doors. In some cases, one of
these white links can become disconnected inside the HVAC case, as shown below
(3).
Correction:
If, after performing normal SI diagnostics, the cause has been determined to be an issue within the HVAC case,
then perform the following:
1. Remove the Evaporator Air Temperature (EAT) sensor (4) from the HVAC case, as shown below. Next, using a
bore scope through the opening for the EAT sensor (5), inspect both driver side temperature doors while
changing the HVAC temperature setting from full cold to full hot, or while manually rotating the driver side
temperature door shaft with the temperature actuator removed. See first photo above for the relationship
between the driver temp doors and EAT opening (4).
– If the temperature doors are moving through their full travel, then continue to Step 2.
– If a temperature door is not moving, or not moving properly, then this could be an issue with a white link
disconnected, temperature door issue, or an actuator issue. Perform normal diagnostics to determine the root
case. It may be necessary to disassemble the HVAC case to determine the root cause of a door issue and then
replace any parts that are necessary.
2. If the driver side temperature doors are moving through their full travel then:
Vehicles not equipped with RPO L5P engine, see Bulletin 21-NA-237 for repair info.
Vehicles equipped with RPO L5P engine perform the following:
– Check for low coolant level in the surge tank bottle
– Check to be sure that the surge tank cap is properly installed and holds pressure
– Check for leaks in the system (check connections and confirm the rear heater operates correctly on the SUV)
– Drain coolant system and note:
– Any sludge in the radiator lines
– If the coolant is liquid or sludge during draining process
– Flush the coolant system to remove any contaminants.
– Replace the heater core and install new coolant, making sure to use a 50/50 mix of the recommended
coolant and clean drinking water.
– Con􀃪rm system is leak free and operating as expected
Warranty Information
The correction for this concern may be one of several repairs described above.
For vehicles repaired under warranty, please use the appropriate warranty labor operation based on the actual
cause and repair.
Additional SI Keywords
cold, cool, heat, hot,
Version History
Version 1
Modified 11/29/2021 – Created on.

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