Bulletin No.: 23-NA-061

Service Bulletin

Date: August, 2024

INFORMATION
Subject:

Brand:

Chevrolet

GMC

Diagnostic Tip for Checking Exhaust System for Leaks for the L5P
Engines, Malfunction Indicator Lamp (MIL) Illuminated - DTC P0402,
P0421, P11D5, P20EE, P2459, P2463, P249D, and/or P249E

Model:

Model Year:
from

to

Silverado

2017

2018

Silverado 2500HD/
3500HD

2019

2025

Sierra

2017

2018

Sierra 2500HD/
3500HD

2022

2025

Involved Region or Country

VIN:
from

Engine:
to

Transmission:

L5P

North America, Russia, Middle East, Chile, Colombia, Ecuador, Paraguay, Peru, Japan,
Cadillac Korea (South Korea), Thailand, Australia/New Zealand
Some customers may comment on one or more of the following conditions:
• MIL illuminated
• Exhaust odor
• Hiss, whine, squeal, whistle, tick, screeching, flutter, or howling noise during exhaust
brake
• Whining

Condition

Technicians may comment on one or more of the following DTCs set in the Engine Control Module (ECM):
• P0402: Exhaust Gas Recirculation (EGR) Flow Excessive
• P0421: Catalytic Converter Low Efficiency
• P11D5: Nitrogen Oxides Sensor 2 Exceeded Minimum Learning Limit
• P20EE: Nitrogen Oxides Catalytic Converter Efficiency Below Threshold
• P2459: Particulate Filter Regeneration Frequency
• P2463: Particulate Filter Soot Accumulation
• P249D: Closed Loop Reductant Injection Control At Limit - Flow Too Low
• P249E: Closed Loop Reductant Injection Control At Limit - Flow Too High

Cause

Correction

This condition may be caused by an exhaust leak.
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.

Copyright 2024 General Motors. All Rights Reserved.

Page 2

August, 2024

Bulletin No.: 23-NA-061

• 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.

5245378

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

Bulletin No.: 23-NA-061

August, 2024

Page 3

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

6140930

6306792

5. Install the inflatable adapter for the GE-52250
machine and insert it into the tailpipe.
6. Attach the GE-52250 to the adapter and shop air
supply.
7. Command the vapor test and adjust the test
pressure to 34–55 kPa (5-8 psi).

8. 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).
9. Once all the leaks are detected and corrected,
verify that the exhaust is sealed by retesting with
the GE-52250.

Page 4

August, 2024

Bulletin No.: 23-NA-061

Examples of Exhaust Leak Areas of Concern
Examples of leaks: This is considered an acceptable
leak from the turbocharger:

6306801

Left side exhaust manifold
6306794

Exhaust temp sensor

Example of Normal Exhaust Leak Area

6306802

6306796

Normal turbocharger seal leakage

DEF Injector

Version

3

Modified

Released March 31, 2023
Revised June 05, 2023 - Revised Subject.
Revised August 09, 2024 - Added 2025 to Model Year.

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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