Bulletin No.:

Service Bulletin

Date:

22-NA-168
August, 2022

INFORMATION
Subject:

Diagnostic Tip for Checking Exhaust System for Leaks, Malfunction Indicator Lamp
(MIL) Illuminated - DTC P2C7A and/or P0421 Set

Brand:

Model:

Cadillac

Escalade
Models

2021

2023

Silverado
1500

2020

2021

2022

2022

Suburban

2021

2023

Tahoe

2021

2023

Sierra 1500

2020

2021

2022

2022

2021

2023

Silverado
1500 - New
(RPO J22,
VIN Digit
5 = A/D)

Sierra 1500 Limited
(RPO J21,
VIN Digit
5 = 8/9)
GMC

VIN:
to

Silverado
1500 - LTD
(RPO J21,
VIN Digit
5 = W/Y)
Chevrolet

Model Year:
from

Sierra 1500 New (RPO
J22, VIN
Digit 5 =
H/U)
Yukon
Models

Copyright 2022 General Motors LLC. All Rights Reserved.

from

to

—

—

Engine:

Transmission:

Duramax 3.0L
Turbo Diesel
(RPO LM2)

—

Page 2

August, 2022

Bulletin No.: 22-NA-168

Involved Region or Country

North America, Russia, Middle East, Chile, Colombia, Ecuador, Paraguay, Peru, Japan,
Cadillac Korea (South Korea), Thailand, Australia/New Zealand

Condition

Some customers may comment that the MIL is illuminated.
Technicians may comment on one or more of the following DTCs set in the Engine
Control Module (ECM):
• P2C7A: Nitrogen Oxides Catalytic Converter 2 Efficiency Below Threshold
• P0421: Catalytic Converter Low Efficiency

Cause

This condition may be caused by an exhaust leak that will let oxygen into the exhaust and
will make the Nitrogen Oxide sensors read incorrectly.

Correction

There are two different types of leak tests that can be performed on the induction or
exhaust system. The first is a smoke leak test where the area being tested is filled with
pressurized smoke and the leak is detected by visually inspecting for smoke exiting the
system. The second is a pressure leak test where soapy water is applied to the outside of
the area being tested and leaks are visually identified by the presence of bubbles forming
over the leaking area.
Advantages to using a Smoke leak test vs. a Pressure leak test:
• Smoke is easy to see exiting relatively large leak locations. The smoke bellows out.
• You can sometimes smell the smoke to help identify a leak location.
Disadvantages to using a Smoke leak test vs. a Pressure leak test:
• Smoke is hard to see exiting a small leak as the smoke is traveling fast.
• Smoke can be removed when it passes through a DPF.
Advantages to using a Pressure leak test vs. a Smoke leak test:
• Bubbles will easily form over a small leak making it easy to spot.
• You can leave soapy water on the surface being tested while you go to eat lunch.
When you return, you should still see bubbles.
Disadvantages to using a Pressure leak test vs. a Smoke leak test:
• It is very difficult for a soap film to form over a large leak to make a bubble.

Important: Service agents must comply with all
International, Federal, State, Provincial, and/or
Local laws applicable to the activities it performs
under this bulletin, including but not limited to
handling, deploying, preparing, classifying,
packaging, marking, labeling, and shipping
dangerous goods. In the event of a conflict between
the procedures set forth in this bulletin and the
laws that apply to your dealership, you must follow
those applicable laws.

Service Procedure
Note: A leak at the turbocharger vane actuator shaft is
considered a normal condition. Any smoke or bubbles
from this area should be ignored.

Bulletin No.: 22-NA-168

August, 2022

Page 3

5150254

1. Remove the air filter (3) from the air filter housing.
Refer to Air Cleaner Element Replacement in SI.

6140932

6140930

2. Put the air filter in a plastic bag.
3. Re-install the air filter into the air filter housing.
4. Raise the vehicle.

5. Locate the cooling ports in the exhaust system.

Page 4

August, 2022

6140943

Note: The graphic depicts a single exhaust system. If
equipped with a dual exhaust, both cooling holes will
need to be taped off and one of the tail pipes sealed
with a rag or equivalent.
6. Tape the holes utilizing duct tape or equivalent.

Bulletin No.: 22-NA-168

6140928

7. Install the inflatable adapter (second largest
adapter for our application) for the GE-52250
machine and insert it into the tailpipe.
8. Attach the GE-52250 to the adapter and shop air
supply.
9. Command the vapor test, and adjust the test
pressure to 34–55 kPa (5-8 psi).
10. Using a soapy water mixture, spray all
connections, welds, and sensors with the soapy
water mixture, and look for air leaks (See
Examples of Exhaust Leak Areas of Concern
section below).
11. Once all the leaks are detected and corrected,
verify that the exhaust is sealed by retesting with
the GE-52250.

Bulletin No.: 22-NA-168

August, 2022

Page 5

6141008

LM2 After Treatment Exhaust System
Note: The areas that have been marked on the graphic
require inspection for leaks.
Exhaust Leak Areas of Concern
1

Turbocharger

2

V-Band Clamp

3

NOx Sensor

4

Def Injector

5

LP EGR Cooler

6

EXH. Throttle/Back
Pressure Valve

7

NOx 2 Sensor

8

NOx 3 Sensor

9

Particulate Matter Sensor

10

Norma Band Clamp

Page 6

August, 2022

Bulletin No.: 22-NA-168

Examples of Exhaust Leak Areas of Concern

6140937
6140935

6140940
6140936

Version

1

Modified

Released August 12, 2022

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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