21-NA-123

Bulletin No.:
Service Bulletin
Date:
21-NA-123
January, 2023
TECHNICAL
Subject:
Rough Idle with Misfire Counts on Random Cylinders, Malfunction Indicator Lamp
(MIL) Illuminated
This bulletin replaces PIP5715B. Please discard PIP5715B.
Brand:
Model:
Chevrolet
Corvette
Model Year:
VIN:
from
to
from
to
2020
2023
—
—
Engine:
Transmission:
6.2L (RPO LT2)
—
Involved Region or Country
North America, Paraguay, Europe, Uzbekistan, Middle East, Japan, GM Korea Company,
China
Condition
Some customers may comment on a rough idle condition and/or the MIL may be
illuminated.
– This is typically noticed on vehicles at low mileage (like PDI) or vehicles that may have
been started then shut off multiple times such as marshaling. Upon inspection, the
technician may also notice random misfires on multiple cylinders.
Cause
This condition may be caused by marshalling the vehicle around and/or short runtime
soot, fouling the spark plugs.
– The LT2 engine in the Corvette is a very capable and powerful powerplant, the jewel
within the all-new mid-engine design. Producing 495 horsepower at 6450 rpm and 470
lb-ft. of torque at 5150 rpm with performance exhaust, this engine produces more
naturally aspirated HP per liter of displacement than any Corvette engine in history.
– To fully enable this extreme level of engine performance, the LT2 was designed to be
driven. Like many performance car engines, the LT2 is sensitive to short run-time starts
where the spark plug does not have time to heat up. In these cases, carbon from the
combustion process can accumulate on the spark plug and result in rough idle or
misfire. The best way to keep your spark plugs clean is to safely exercise your
Corvette on your favorite roads or track. Both running your engine and spirited driving
can clean plugs that may be partially impacted.
– Whenever possible, try to run the engine until it has reached a coolant temperature
greater than 51°C (125°F), and/or at least 3 minutes of engine run time, instead of
frequent, short duration start/stop cycles.
If you encounter a vehicle that is in for this condition and meets the criteria above, follow
the Correction steps.
Correction
If you encounter this condition, utilizing the GDS2, command the engine speed up to
2000 rpm for 10 minutes and re-evaluate the concern.
• If the misfires stop counting, return the vehicle to the customer.
• If the concern is not completely gone, the vehicle may need to be driven to finish
cleaning the spark plugs.
• If the above steps do not resolve the concern, it will be necessary to replace all 8
spark plugs.
Copyright 2023 General Motors LLC. All Rights Reserved.
Page 2
January, 2023
Bulletin No.: 21-NA-123
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
Refer to Gas Engine Ignition Spark Plug Replacement Right Side in the Service Manual and/or Gas Engine
Ignition Spark Plug Replacement - Left Side in the
Service Manual.
Parts Information
Causal
Part
Description
Part
Number
Qty
X
SPARK PLUG,
GAS ENG IGN
12622442
8
Warranty Information
For vehicles repaired under warranty, use:
Labor
Operation
Description
Labor Time
4020870
Gas Engine Ignition Spark
Plug Replacement Left Side
4020871
Gas Engine Ignition Spark
Plug Replacement - Left
Side - Multiple
4020880
Gas Engine Ignition Spark
Plug Replacement Right Side
4020881
Gas Engine Ignition Spark
Plug Replacement - Right
Side - Multiple
Use
Published
Labor
Operation
Time
Version
2
Modified
Released June 29, 2021
Revised January 17, 2023 – Added the 2022–2023 Model Years, Europe to the Involved
Region or Country section, Important statement and Service Procedure.
Additional SI Keywords: P0300, P0301, P0302, P0303,
P0304, P0305, P0306, P0307, P0308
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