Bulletin No.: 24-NA-175

Service Bulletin

Date: August, 2024

TECHNICAL
Subject:

Vibration or Rough Idle while in Drive or Park
This bulletin replaces PIP5798. Please discard PIP5798.

Brand:

Model:

Chevrolet

Silverado 1500

GMC

Sierra 1500

Model Year:
from

to

2019

2021

VIN:
from

Engine:
to

Transmission
:

L82, L84, L87

Involved Region or Country

North America

Condition

Some customers may comment on a rough idle and/or vibration while in drive or while in
park with vehicle idling.
- This condition may be most noticeable when the engine is completely warmed up with
the accessories Off.
Some customers may also comment on a misfire, stumble, loopy/lumpy idle, or may be
described as a low idle.
This condition may be caused by one or more of the following:
• Misfire and/or base engine concern

Cause

• Wrong fuel used (regular instead of premium when required)
• Idle speed fluctuation
• Engine mount pre-load

Correction

If the vibration has been verified. Perform 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
Important: Familiarize yourself with this entire PI before proceeding to ensure you are diagnosing and
focusing on the correct issue by frequency measured with Pico scope.
To correct this concern, follow the steps below.
1. Ensure there are no stored DTC’s. If there are any DTC’s refer to the applicable service procedure in service
information and fix those first.
2. Confirm there are no other warning lights active.

Copyright 2024 General Motors. All Rights Reserved.

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August, 2024

Bulletin No.: 24-NA-175

3. Monitor fuel trim readings and cylinder misfires to confirm there are no concerns. Also make note of the engine
idle speed.
4. Ensure premium fuel is being used (if required).
5. Perform Pico analysis at the driver’s seat track, refer to the Initial Setup/Duplication/Evaluation section below.
Record and save your file as this will be requested by TAC.
− If Pico measurement at E1.5 is above 4mg threshold, refer to Settle all Mounts in the Engine and Transmission Mount Balancing Procedure section below.
6. Re-measure seat track vibration. Record and save your file as this will be requested by TAC.
7. If E1.5 measurement does not improve, replace engine mounts, then re-measure to confirm mount replacement
improved the E1.5 seat track vibration to a value below 4 mg. Record and save your file as this will be
requested by TAC.
Note: If after settling the engine mounts or replacing them and you find the vibration condition is still not
acceptable it will be necessary to open a TAC case and attached your files to the case. Reference PIP5601B
for further instructions on how to upload the files. If the condition was corrected following one of the procedures above print and attach your “before and after” Pico results to the repair order.

4532459

4532456

Bulletin No.: 24-NA-175

August, 2024

Page 3

(TA183 single axis Pico sensor shown / TA143 is tri-axis sensor).
Add E1.5 to the displayed data and turn Off T and P related data (under Add Vibration in Pico) since issue occurs
with vehicle stationary.

5786964

Note: Amplitude (mg) readings from a single-axis Pico sensor will be approximately 10% lower than with a tri-axis
sensor. For example, a reading of 4 mg using a tri-axis sensor, would likely measure as about 3.6 mg on a singleaxis sensor.
If the disturbance frequency measures at the seat track as E1.5 with amplitude of approximately 2 mg or higher
using a tri-axis sensor, continue with steps in this bulletin to reduce the amplitude (mg) of the disturbance, then
exercise the vehicle and re-measure using Pico to determine level of improvement.

Engine and Transmission Mount Balancing Procedure
Note: Before replacing engine mounts, ensure the exhaust system is not bound up and the rear transmission mount
is clear of any debris and/or not damaged. Either of these can result is a higher-than-normal Pico result.
Important: For any engine mount to frame bolts removed during this process. Replace the engine mount to frame
bolts with NEW bolts.
Important: Do Not use Impact wrenches when tightening the engine mount to frame bolts or damage to threads in
the frame may result.
Important: Both LH and RH engine mounts need to be seated to the vehicle frame at the same time to help
ensure best alignment.
Note: Initial removal of the engine mounts will require the removal of the exhaust manifolds.
1. If replacing both engine mounts (1), refer to Engine Mount Replacement – Left and Right Engine Mount
Replacement in SI.
2. Install but do NOT tighten the mount to frame bolts.
Settle all Mounts as follows:
⇒

Ensure the engine mount to frame bolts on both LH and RH sides are loosened a couple turns.

⇒

Ensure the transmission/transfer case mount to frame crossmember nuts are loosened a couple of turns.

⇒

Have assistant set park brake and apply base brake.

⇒

With the engine at operating temperature, have assistant turn Traction Control Off and brake torque in Drive and
Reverse.

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⇒

August, 2024

Bulletin No.: 24-NA-175

Place in Neutral and turn engine Off.

New Engine Mount Balancing Procedure

5786963

5786962

1. In Neutral, with engine Off, using Only Hand Tools, torque all the new engine mount to frame bolts (1) in
sequence shown. - 109 ft. lbs. (80 Nm) + 35-40 degrees
2. Torque the transmission/transfer case mount to crossmember nuts to 85 ft. lbs. (115 Nm).
3. Re-evaluate the rough idle vibration – repeating steps under Initial Setup/Duplication/Evaluation.
4. Monitor fuel trim readings and cylinder misfires to confirm there are no concerns. Also make note of the engine
idle speed.
5. Ensure premium fuel is being used (if required).
6. Perform Pico analysis at the driver’s seat track, refer to the Initial Setup/Duplication/Evaluation section below.
Record and save your file as this will be requested by TAC.
⇒

If Pico measurement at E1.5 is above 4mg threshold, perform the Engine and Transmission Mount Process.

Bulletin No.: 24-NA-175

August, 2024

Page 5

7. Re-measure seat track vibration after following the Engine and Transmission Mount Process. Record and save
your file as this will be requested by TAC.
Note: If after settling the engine mounts or replacing them and you find the vibration condition is still not acceptable
it will be necessary to open a TAC case and attached your files to the case. Reference PIP5601B for further instructions on how to upload the files. If the condition was corrected following one of the procedures above print and
attach your “before and after” Pico results to the repair order.
Note: Before replacing engine mounts ensure the exhaust system is not bound up and the rear transmission mount is clear of any debris and not damaged. Either of these can result is a higher-than-normal
Pico result.
Note: The 6.2L engine has a characteristic E1 which can be felt and may be described as a loopy idle. V-8 engine
firing frequency produces E4 which will typically be very low frequency at the seat track. Do not confuse 6.2L E1
characteristic, with E1.5 (engine roll frequency) normal idle characteristics being transmitted into the truck.

Initial Setup/Duplication/Evaluation
Measure the vibration disturbance using the vibration analyzer, CH-51450-A (Pico Oscilloscope), to qualify whether
the issue frequency is E1.5 as opposed to E1 or E4:
Note: If using a single-axis Pico sensor, mount, and test both vertically and horizontally – E1.5 rough idle vibration
will usually be horizontal/lateral at the seat track.
Important: If the E1.5 disturbance measures approximately 4 mg or lower using the Pico tri-axis sensor as indicated
– the vehicle is considered acceptable.
1. Place tri-axis Pico sensor on the inboard seat track forward-most location to record measurement of the rough
idle vibration concern.
Note: Most rough idle in Drive concerns are temperature dependent and can be difficult to re-create at times.
2. With A/C On, perform several short heavy launch events from stop to stop to bring the temperatures back up
while attempting to re-create the rough idle vibration in Drive with Pico sensor placed on inboard seat track,
while the vibration is active – Record Pico reading. This method seems to provide better results than extended
test drives:
• If the Pico reading for E1.5, with vibration active, at the inboard forward seat track location measures approximately 4 mg or higher – continue following steps in this bulletin to perform the engine and trans mount settling
process.
⇒

After performing the mount settling process and the Pico reading the E1.5 has not improved, then it will be
necessary to replace the engine mounts. Refer to Engine Mount Replacement in SI.

• If the Pico reading for E1.5, with vibration active, at specified seat track location measures close to 4 mg or
less – investigate other sources of the rough idle/vibration concern using SI diagnostics.
• If the E1.5 idle vibration at inboard seat track forward location has been reduced to 4 mg or less – the vehicle
is considered acceptable.

Parts Information
Description

Part Number

Qty

Mount, Engine

Refer to EPC

1 Set

BOLT, ENG MT FRM SI

Refer to EPC

3

GASKET, EXH MANIF

Refer to EPC

1 Per Side

BOLT, EXH MANIF

Refer to EPC

5 Per Side

SEAL, EXH SYS L

Refer to EPC

1

SEAL, EXH SYS R

Refer to EPC

1

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August, 2024

Bulletin No.: 24-NA-175

Warranty Information
For vehicles repaired under the Powertrain coverage, use the following labor operation. Reference the Applicable
Warranties section of Investigate Vehicle History (IVH) for coverage information.
Labor
Operation

Description

Labor Time

4087928*

Engine Mount Settling
Procedure includes
Perform Pico Scope Idle
Vibration Measurements

2.0 Hours

4087948*

Engine Mount
Replacement

13.4 Hours

*This is a unique Labor Operation for Bulletin use only.

Version

1

Modified

Released August 29, 2024

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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