Lack of Power or Poor Performance During High Ambient Temperatures with RPO (C7N) 12,300 LB GVWR or (C4M) 9,900 LB GVWR – 2016-2020 Chevrolet Express & GMC Savana

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Service Bulletin Bulletin No.: 21-NA-260
Date: December, 2021
TECHNICAL
Subject: Lack of Power or Poor Performance During High Ambient Temperatures with RPO
(C7N) 12,300 LB GVWR or (C4M) 9,900 LB GVWR
Brand: Model:
Model Year: VIN: Engine: Transmission:
from to from to
Chevrolet Express
2016 2020 6.0L,
L96 LC8 All
GMC Savana
Involved Region or Country United States, Canada
Additional Options (RPOs)
Condition
Some customers may comment that the vehicle exhibits a lack of power when driving up
grades or after the vehicle has been idling for long periods of time in high ambient
temperatures (90 degrees, 32 Celsius or above). This condition is more noticeable when
the vehicle is outfitted with heavy work equipment on the back such as work boxes or
ambulance bodies. When the ambient temperature drops below 90 degrees (32 Celsius)
you may notice that the condition is less noticeable or eliminated altogether.
Page 2 December, 2021 Bulletin No.: 21-NA-260
Cause
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The cause of the condition may be high ambient temperatures 90 degrees (32 Celsius)
effecting the intake air flow to the engine. When looking at GDS2 scan tool data you may
also notice an increase in total knock retard and ignition timing being backed out (chart
shown above). This can occur while the vehicle is underload or driving in a situation
where they may be going up a grade and more throttle input is required. The ECM is
adjusting to protect the engine from engine damaging spark knock, which are normal
under these conditions.
Correction
A new air inlet duct extension has been released to fix this concern. Before installing the
new air inlet duct extension, please inspect the following list of items to ensure they
installed correctly, and not missing or damaged. If any one of these components is
missing or damaged, this could allow hot air into the intake duct causing the lack of power
concern and must be corrected as well.
Bulletin No.: 21-NA-260 December, 2021 Page 3
Items to Inspect
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– Is the hood seal installed (1) ?
– Are both CRFM side baffles, driver and passenger side, installed correctly (2) ?
– Are both grille seals installed correctly (3) ?
– Is the hood latch seal installed correctly (4) ?
– Is the radiator upper baffle installed correctly (5) ?
– Is the lower baffle installed correctly (6) ?
– Is the air box end cover installed properly ?
– Are all intake air ducts installed correctly and clamps tight ?
– Is the PCV hose installed correctly ?
– Is the air box attached to upper tie bar with correct fasteners and secure ?
– Has the up-fitter installed components in front of the grille, blocking fresh air flow to
CRFM ?
– Has the up-fitter modified anything to attach their components ? (Baffles, fascia, hood
seal or anything else)
– Are there any holes cut/drilled in any sheet metal near the AIS inlet ?
– Inspect the intake duct for any restrictions.
Page 4 December, 2021 Bulletin No.: 21-NA-260
Service Procedure for Installing New
Air Inlet Duct
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1. Remove the radiator air upper baffle (1). Refer to
the appropriate Radiator Air Upper Baffle
Replacement, in SI.
4839923
Bulletin No.: 21-NA-260 December, 2021 Page 5
Note: It is not necessary to completely remove the
grille.
2. Remove the 4 front grille upper bolts (1). Refer to
the appropriate Front Grille Replacement in SI.
3. Using a grease marking pencil, or suitable marker,
mark the locations for removal of grille material,
following the steps below:
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3.1. Locate the right side, standing center ribs on
the grille, shown circled in the graphic above.
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3.2. On the left side of the inboard rib, draw a line
(1) 5.7 cm (2.25 in) from the rib and draw a
second line (2), 8.9 cm (3.5 in) from the rear
edge of the grille.
3.3. On the right side of the outboard rib, draw a
line (3) 14 cm (5.5 in) from the rib and draw a
second line (2), 8.9 cm (3.5 in) from the rear
edge of the grille.
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Note: DO NOTcut through either standing rib. Those
must be kept intact.
4. Using a suitable saw, cut along edges of the
standing ribs and the marked lines.
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5. The grille will now have openings on either side of
the standing ribs.
Page 6 December, 2021 Bulletin No.: 21-NA-260
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6. Using the new engine air inlet duct as a template,
position the duct to the vehicle and drill 6.5 mm (1/
4 in) holes in the grille to allow for the addition of 3
push retainers. However, do not install the engine
air inlet duct and retainers at this time.
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7. Again, using a grease marking pencil, or suitable
marker, mark 3 lines (1) on the radiator air upper
baffle, which will designate material removal to
allow for clearance of the engine air inlet duct
when, the baffle is reinstalled.
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8. Using a suitable saw, cut along the marked lines.
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Note: The RTV sealant is to be applied onto the
extended lip, around the perimeter of the upper opening
of the engine air inlet duct, where it interfaces (1) with
the opening of the intake duct.
Bulletin No.: 21-NA-260 December, 2021 Page 7
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9. Apply RTV Engine sealant around the complete
perimeter of the upper opening of the engine air
inlet duct, at the interface to the intake duct.
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10. Install the engine air inlet duct and the 3 push
retainers to the vehicle.
Page 8 December, 2021 Bulletin No.: 21-NA-260
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11. Reinstall the 4 front grille upper bolts (1). Refer to
the appropriate Front Grille Replacement in SI.
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12. Reinstall the modified radiator air upper baffle (1)
to the vehicle. Refer to the appropriate Radiator Air
Upper Baffle Replacement, in SI.
Parts Information
Causal
Part
Description Part
Number
Qty
N/A
DUCT-FRT
INT AIR
85533626 1
SEALANT,RTV
SILICONE TUBE
TB 1217 AC
DELCO 2.65 OZ
88864346
(U.S.)
88861418
(Canada)
As needed
PIN – PUSH 11589290 3
Bulletin No.: 21-NA-260 December, 2021 Page 9
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
4088278* Modify Grille and Radiator Air Upper Baffle, Install New Engine
Air Inlet Duct 1.0 hr
*This is a unique Labor Operation for Bulletin use only.
Version 1
Modified Released November 29, 2021

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