Service Bulletin

Bulletin No.:

21-NA-124

Date:

May, 2021

INFORMATION
Subject:

Diagnostic Tip for Malfunction Indicator Lamp (MIL) Illuminated - DTC P0442 and/or
P0455 Set

Attention: This bulletin only applies to vehicles with gasoline engines.
Brand:

Model:

Buick

GM
Passenger
Cars and
Trucks
(including
Medium
Duty)

Cadillac
Chevrolet
GMC

Model Year:

VIN:

from

to

from

to

2000

2021

—

—

Engine:

Transmission:

All Gasoline
Engines

—

Involved Region or Country

North America, Europe, Uzbekistan, Russia, Middle East, Iraq, Israel, Palestine,
Argentina, Brazil, Bolivia, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay,
Venezuela, Japan, Cadillac Korea (South Korea), GM Korea Company, China, Taiwan,
Thailand, Singapore, Philippines, Australia/New Zealand, Egypt, Other Africa, South
Africa

Condition

Some customers may comment that the MIL is illuminated.
Some technicians may find one or more of the DTCs set in the Engine Control
Module (ECM):
• P0442: Evaporative Emission System Small Leak Detected
• P0455: Evaporative Emission System Large Leak Detected

Information

Refer to the Service Procedure below for some diagnostic tips that may help locate the
source of the leak or cause of the concern.

Service Procedure
Note: For diagnostic instructions, DTC information and
tools required, remember to always follow the service
information (SI) document associated to the applicable
vehicle and DTC you are working on.
For DTC P0455 (large leak detected), the vehicle will
set the code due to large leak or purge blockage. A
large leak can occur from an unseated tube connection,
a damaged tube, a stuck opened canister vent valve or
a stuck closed purge valve.
For DTC P0442 (small leak detected), the vehicle will
set this code due to small leak. The leak can occur from
a stuck open purge valve or stuck open canister vent
valve. In addition, the DTC could set due to an
unsealed EVAP system, so verifying all purge lines are
properly connected should be confirmed.
For either DTC P0442 or P0445, it is crucial to
investigate the EVAP system was properly assembled.
All purge connections must be inspected for proper
installation. While inspecting the line connections, look

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for any signs of damage or wear along the lines. If any
damage is observed, proceed to confirm via the
smoke test.
Note: Some leaks will only be noticeable under
pressure and some only noticeable under vacuum. We
recommend checking both ways. Also cycling the purge
and vent solenoids with GDS2 while inspecting may
indicate a sticking valve.
There are seven critical connections that could likely
lead to these DTCs being set:
1. Purge tube to purge valve (at intake manifold)
2. Purge tube to chassis EVAP line (at rear of engine,
near transmission)
3. Chassis EVAP line to canister (at canister)
4. Fuel tank load line to canister (at canister)
5. Vent valve line to vent valve (at vent valve)
6. Fuel tank load line jumper connection (near
fuel tank)
7. Fuel tank cap is closed properly (at refuel
compartment)

Page 2

May, 2021

Bulletin No.: 21-NA-124

It is likely that either one of these connections is not
properly seated or the line itself is damaged.
⇒ If all connections are good, the vent valve should
be checked for a stuck open position.
⇒ If the vent valve is verified to be functioning
correctly, proceed to investigate the purge valve.
Hence, the following steps should be taken in
chronological order:
1. Investigate all EVAP lines are properly installed
and fully seated.
2. Investigate for any damage on the EVAP lines.
3. Investigate potential vent valve malfunction.
4. Investigate potential purge valve malfunction.
Based on what is found, be sure to document the cause
and correction on the repair order.

Parts Information
No parts are required for this repair.
Version

1

Modified

Released May 25, 2021

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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