Service Bulletin

Bulletin No.:

19-NA-044

Date:

May, 2021

INFORMATION
Subject:

Information on Black Smoke, Rough Idle and Minimal Misfires on Cold Start

This bulletin replaces PIP4919E, PIP5189C and PI1223B. Please discard PIP4919E, PIP5189C
and PI1223B.

Attention:This bulletin applies to all vehicle
models equipped Direct Injected (DI) gasoline
engines only.
Brand:

Model:

Buick

GM
Passenger
Cars and
Light Duty
Trucks

Cadillac
Chevrolet
GMC

Model Year:
from

2008

VIN:
to

2021

from

—

to

—

Engine:

Transmission:

Direct
Injected (DI)
Gasoline
Only

—

Involved Region or Country

North America, Europe, 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 on black smoke, rough idle, and minimal misfires on cold
start.
Some customers may also state that the malfunction indicator lamp (MIL) is not
illuminated.

Information

With the introduction of direct fuel injection systems, GM has revised the cold start control
system to reduce cold start emissions. Quicker catalytic converter heating helps meet the
ever-changing emission requirements and improve fuel economy.

Additional Information
A dual-pulse injection strategy is utilized during engine
cold start to reduce the time required to bring the
catalytic converter up to operating temperature. This
dual-pulse injection strategy lasts for about 60 seconds
on cold start.
This process will cause the customer to see increased
black smoke, soot, rough idle, or minimal misfires
during cold start and should be considered normal.
To verify that the dual-pulse injection is causing the
roughness or misfires with no codes set, you should
watch injector pulse width with the scan tool during the
concern. Dual pulse injector pulse width will be nearly
double that of normal idle. After 20 seconds the pulse
width will drop by about 50% and the engine idle will
smooth out. This is considered normal operation and no
repairs should be attempted.
Copyright 2021 General Motors LLC. All Rights Reserved.

This cold start strategy is enabled upon start up after
the engine has soaked for sufficient time such that the
catalytic converter requires rapid reactivation.
The high-pressure fuel pump test will run either as soon
as the dual pulse injection is completed, or during the
first stop after the engine is warmed up above about
155°F (68°C). This can feel like a slight idle roughness
as the high-pressure fuel pump is commanded to max
pressure and then shut off to measure pressure decay.
Note: The use of TOP TIER fuels lessens the rough
idle condition effects during dual pulse injection and the
fuel pump test by reducing the amount of carbon on
valve train components and a more complete
combustion leading to cleaner burn. Refer to the latest
version of Service Bulletin #05-06-04-022 — TOP TIER
Detergent Gasoline and TOP TIER Diesel Fuel
Information and Licensed Brands.

Page 2

May, 2021

Bulletin No.: 19-NA-044

All of these concerns are considered normal and no
repair attempts should be made.

Parts Information
No parts are required for this repair.
Version

2

Modified

Released March 01, 2019
May 03, 2021 – Updated PI reference in Supersede statement, added the 2020–2021
Model Years and updated the Involved Region or Country section.

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.

WE SUPPORT VOLUNTARY
TECHNICIAN
CERTIFICATION