Bulletin No.: PIP5504B
Published date: 10/3/2019

Preliminary Information
PIP5504B Diagnosing Fishbite Chuggle Mis re Feeling Or Shudder
Vibration, With A Light Tip In
Models
Brand:

Model:

Model Years:

VIN:
from

to

Engine:

Transmissions:

Chevrolet

Silverado

2016 - 2019

All

All

L83

MYC

Chevrolet

Suburban

2016 - 2019

All

All

L83

MYC

Chevrolet

Tahoe

2016 - 2019

All

All

L83

MYC

GMC

Sierra Models

2016 - 2019

All

All

L83

MYC

GMC

Yukon Models

2016 - 2019

All

All

L83

MYC

Involved
Region or
Country

Condition

Cause

North America and N.A. Export Regions.
Some customers may comment on any of the following conditions.
A shake and/or shudder during light throttle acceleration between 48 and 104
km/h (30 and 65 mph) steady state driving when transmission is not actively
shifting gears.
A shudder feeling that may be described as driving over rumble strips or rough
pavement.
A shudder feeling that is evident in both Drive and M5 mode.
Please refer to the following information to aid in addressing these types of
conditions.

Definitions:
In general if there is insufficient engine firing pulse isolation or combustion instability,
vibrations can be transmitted to the driver typically through the steering wheel, seat track,
or accelerator pedal.
1. Fishbite: (also called Surge, nudge, jerk and bump) is a jerk or bump which may be
transmitted through the Torque Converter Clutch due to insufficient damping or TCC locking
and releasing.
2. Chuggle: (often called boom) is induced from engine combustion exciting the driveline due
to insufficient isolation. Frequency of the boom is affected by driveline mass, stiffness,
damping, and gear.
3. Misfire: or knock is the engine having an irregular combustion event.
4. AFM Disturbances can be mislabeled as any of the definitions above as well as shudder
below, but in fact has to do with the imbalance caused by less cylinders firing.
5. Torque Converter Shudder/Vibration: Any vibration induced by the torque converter clutch
in normal driving mode (with an expected TCC slip amount). (Most often due to TCC friction
material/ATF degradation)
Important – DEXRON 6 is the only approved ATF to be used with 6L (MYA, MYB, MYC, MYD)
transmissions at this time.

Diagnosis/Test Instructions:
Verify and correct any DTC’s prior to proceeding with next steps.
The use of the PICO scope and NVH software should be used to confirm the Disturbance
Frequency and allow the user to see if the disturbance tracks to engine speed (Chuggle,
Misfire), road speed (Tire Vibrations), or remains constant across various inputs (TCC
Shudder). Place the PICO Scope pick up on a metallic component where vibration can be
felt the most (seat track, steering wheel column, accelerator pedal, etc).
a. - Evaluate within customer complaint range (note if concern occurs in V4 or V8
mode).
b. - Evaluate at Idle (Warm & Cold Start).
c. - Evaluate in multiple gears.
A smooth road is desirable for evaluations to isolate concerns without introducing road
inputs/noise.
Minimize extraneous vibration input by testing on a smooth road and correct any other
known vehicle vibration issues (tires, brakes, etc.) before conducting test.
1. Fishbite – Condition can be best isolated by placing the transmission in manual range
5th gear to turn off V4 mode and monitoring TCC Slip in GDS2. With engine speed
between 1,000 – 1,600 rpm and engine load up to 320 Nm the calibration target is 20
rpm of TCC slip in V8 mode. Under these conditions, slip should not be less than 5 rpm
with steady throttle input. (Note: At 400Nm engine load, the calibration target is 5 rpm
of TCC slip.)
2. Chuggle – Condition can be best isolated in Manual 5th gear while in V8 mode, greater
than 320 Nm of engine torque, and engine speeds between 1,200–1,300 rpm when
tipping into throttle to load the engine. Can be confirmed by using GDS2 to Command
TCC on - condition should be the same with TCC locked. This can be Engine 1st Order
Vibration on the PICO Scope as well.
3. Misfire – Can be viewed in GDS2 under engine control module and then selecting misfire
data. This will prompt a screen that will show misfire by each cylinder if the tab
Diagnostic Data Display is clicked. This can be Engine 1st Order Vibration on the PICO
Scope as well.
4. AFM Disturbances – While monitoring the Driver Information Center to display V4 or V8
mode, determine if the disturbance only occurs in V4 mode or during the transition
between V8 and V4 mode.
5. Torque Converter Shudder/Vibration – Condition can be best isolated with transmission
temperature between 40°C (104°F) - 89°C (192°F). Drive the vehicle in 6th gear, V8
mode, with a transmission input speed of 1,000–1,500 rpms (approximately 64-89 km/h
(40–55 mph)), constant throttle input, and engine torque 250-375 Nm.
Important: For some road conditions, it may be required to apply the brake pedal and
throttle simultaneously to stay within desired engine torque range.
Press and hold the tow-haul mode button for 5 seconds to disable grade braking to
prevent downshifts during test.

Run the test in 3 operational modes:
- Normal Operation (TEHCM commanding TCC apply. Use GDS2 for viewing only).
- GDS2 Commanding TCC in Disabled Operation. (No TCC Apply).
- GDS2 Commanding TCC in Enabled Operation. (TCC Locked).
To confirm TCC Shudder, the vibration concern must be present in normal operation
(Mode A), but not present with the torque converter clutch disabled (Mode B) or with
the torque converter clutch locked (Mode C).
If the concern is not present in Mode A, then the vibration concern is NOT TCC
Shudder.
If the concern is still present with the torque converter clutch disabled (Mode B) or
with the torque converter clutch locked (Mode C), the root cause of vibration is NOT
TCC shudder.

If TCC Shudder is present, a vibration peak will appear at approximately 43Hz +/-3Hz
as shown in the picture above. If the vibration frequency follows engine, tire, or
driveshaft speed, then it is NOT TCC Shudder. TCC Shudder vibration frequency should
stay constant per gear while vehicle and engine speeds change.
Vibrations not identified as shudder should be further investigated using the “Vehicle
Vibration Diagnosis” in SI as a starting point. Use of the PICO scope and NVH software
can be used to confirm TCC Shudder, Engine, Tire or Driveline component related
conditions.
Vibrations identified as shudder should be further investigated using the "Torque
Converter Diagnosis" in SI as a starting point.

Version History
Version

Modi ed

2
06/19/2017 - Created on.
01/17/2018 Updated Model Years
10/03/2019 - Added the 2019 model year and removed the
repair recommendation if TCC shudder is confirmed. Added to
refer to Torque Converter Diagnosis in SI if TCC shudder is
confirmed.

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