Bulletin No.:

Service Bulletin

Date:

20-NA-166
August, 2020

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 bulletin replaces PIP5498M. Please discard all copies of PIP5498.

Brand:
Cadillac

Chevrolet

GMC

Model:
CTS

Model Year:

VIN:

from

to

2016

2020

from

to

Engine:

Transmission:

LT4

Escalade

2015

2020

L86

Camaro

2016

2020

LT1, LT4

Corvette

2016

2019

LT1, LT4, LT5

Silverado

2014

2018

L83, L86

Silverado
1500 (New
Model)

2019

2020

L82,
L84, L87

Silverado LD

2019

2019

Suburban

2015

2020

L83

Tahoe

2015

2020

L83

—

—

L83

Sierra

2014

2018

L83, L86

Sierra 1500
(New Model)

2019

2020

L82,
L84, L87

Sierra
Limited

2019

2019

L83

Yukon

2015

2020

L83, L86

—

Involved Region or Country

North America, Europe, Russia, Middle East, Israel, Argentina, Chile, Colombia, Ecuador,
Venezuela, Japan, Cadillac Korea (South Korea), China, Taiwan, Thailand, Singapore,
Philippines, Other Africa

Condition

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.

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.
Copyright 2020 General Motors LLC. All Rights Reserved.

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:

Page 2

August, 2020

Bulletin No.: 20-NA-166

•

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.
4806659

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

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. 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.

Bulletin No.: 20-NA-166

August, 2020

Page 3

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.

Parts Information
No parts are required for this repair.

Version

1

Modified

Released August 21, 2020

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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