Bulletin No.: 20-NA-166

Service Bulletin

Date: January, 2025

INFORMATION
Subject:

Information on Malfunction Indicator Lamp (MIL) Illuminated – DTCs P050D
and/or P0300 Setting on a Cold Start and/or Engine Runs Rough when Warm
with No Codes

This Service Bulletin replaces PIP5498M. Please discard all versions of PIP5498.
Brand:

Model:

Model Year:
from

Cadillac

2019

CT5

2022

2025

Escalade

2015

2025

Camaro

2016

2024

Corvette

2016

2025

Silverado

2014

2018

Silverado 1500
(New Model)

2019

2019

2022

2022

2019

2019

2020

2021

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

Silverado 1500

2023

Suburban

2015

Tahoe

2015

Sierra

2014

2018

Sierra 1500 (New
Model)

2019

2019

2022

2022

2019

2019

2020

2021

Sierra 1500 Limited
(RPO J21, VIN Digit
5 = 8/9)
Sierra 1500 New
(RPO J22, VIN Digit
5 = H)
Sierra Limited
Sierra 1500
Yukon Models

Copyright 2025 General Motors. All Rights Reserved.

2023
2015

Engine:

from

2016

Silverado LD

GMC

to

CTS

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

VIN:

2025

2025

to

—

—

L82, L83, L86,
L84, L87, LT1,
LT2, LT4, LT5

Transmissi
on:

—

Page 2

Involved Region or Country

Condition

January, 2025

Bulletin No.: 20-NA-166

North America, Argentina, Chile, Colombia, Ecuador, Venezuela, Europe, Russia, Middle
East, Israel, Japan, Cadillac Korea (South Korea), China, Taiwan, Thailand, Singapore,
Philippines, Other Africa, Australia/New Zealand
Some customers may comment on one or more of the following conditions:
• The MIL is illuminated.
• Engine runs rough when warm.
Some technicians may find DTCs P050D and/or P0300 setting on a cold start.

Cause

This condition may be caused by coolant getting into the cylinders.

Correction

Validation will be required for possible internal coolant leaking into the cylinders. Refer to
the Service Procedure below.

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
Technical Assistance (TAC) is currently receiving calls after the engine has been disassembled with no trouble found
before completing SI diagnostics for DTC P0300 and P050D.
Note: PLEASE BE SURE TO FIRST FOLLOW SI DIAGNOSTICS for P0300 and P050D THEN, IF DTC P050D
FLOWCHART DOES NOT ISOLATE THE CONCERN, THEN THE FOLLOWING MAY BE HELPFUL:
• Follow the flow chart for the P0300 to validate that there is not an ignition or mechanical concern with or without
the P0300 set.
• When completing the flow P050D chart, be sure you are checking the injector balance rates while the engine is
cold.
• Be sure to record the injector balance rates and attach to the work order.
• If an injector concern is found, replace only the affected injector.
Note: This will need to be done before the engine is disassembled.
Note: If the injectors are being replaced on L86, LT1, LT4 or LT5, there are three different flow rate injectors
offered. Be sure to install the same flow rate injectors back into the engine by checking the part number on the
injector housing. Mixing the flow rates will cause driveability concerns, DTC setting and repeat injector replacements.

Code P050D Description
During a cold start, the engine control module (ECM) commands dual-pulse mode during Open Loop operation to
improve cold start emissions. In dual-pulse mode, the fuel injectors are energized twice during each injection event.
As with misfire diagnosis, in dual-pulse mode the ECM monitors the crankshaft position sensor and the camshaft
position sensor to calculate crankshaft rotation speed.
In normal operation, optimum fuel delivery during dual-pulse mode produces a steady crankshaft rotation speed. If
the variations of crankshaft rotation speed exceed a calibrated value, the code P050D will be set.
Misfires on start up only, with high rates always on one cylinder, can be suspect for coolant entry at the liner to deck
face casting or the casting line in the intake port of the cylinder head.
To inspect for this concern, add coolant dye to the system, run the engine through warm up, pressurize the cooling
system after warming the engine to operating temperature (let the engine cool overnight) and inspect the suspect
cylinder with a borescope for coolant dye evidence.
At times it may be necessary to remove the head for inspection.
If the head casting line is the concern, the intake port will be wet with a coolant oil mix.
This could be the cause of a running rough warm concern with or without codes.

Bulletin No.: 20-NA-166

January, 2025

Page 3

The location of where the coolant is running down in the port will also look washed down.

4806659

If this is found, the cylinder head will need to be replaced.

4806657

It is also possible to have coolant entry at the liner to deck face casting of the cylinder bore (1). It is hard to see the
actual source (pin hole), but it usually streams down the liner so that you can see it with a borescope. (Sometimes)
The top of the piston will be steam cleaned.
Do not confuse residual fuel on the piston crown / surface as coolant. Some fuel residue may be present and can be
mistaken as coolant (reason for the cooling system Dye to be added). Use a black light to confirm the liquid is
coolant. If this concern is present, do not replace the cylinder head because that will not repair this concern. Call the
Product Quality Center (PQC) per Service Bulletins 20-NA-138 (U.S.) or 16-NA-338 (Canada), if required, reference
this bulletin and replace the engine.
Small surface pock marks or pitting appearance on the deck surface is normal and engines should not be replaced
for such appearance as they do not connect to coolant passages and cause a leak path that generate engine
misfires. During engine warranty analysis studies, engines are being replaced for small pitting in the deck face as
described above, when the subject cylinder / piston is saturated with fuel and not coolant.
Engines replaced for light / shallow pitting conditions will be returned to the dealership as non-defective.

Page 4

January, 2025

Bulletin No.: 20-NA-166

Parts Information
No parts are required for this repair.
Version

4

Modified

Released August 21, 2020
Revised December 09, 2021 – Added the 2021-2022 Model Years and Australia/New
Zealand to Involved Region or Country section.
Revised March 21, 2024 – Added the 2023-2024 Model Years to applicable vehicles and
the Important statement.
Revised January 08, 2025 - Added CT5 to Models and 2025 Model Year to Applicable
Vehicles.

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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