Bulletin No.: PIP5504F
Published date: 07/10/2020

Preliminary Information
PIP5504F Diagnosing Fishbite Chuggle Mis re Feeling Or Shudder
Vibration, With A Light Tip In
Models
Brand:

Model:

Model Years:

VIN:
from

Engine:

to

Transmissions:

Chevrolet

Express

2016 - 2020

All

All

L20, L96, LC8, LGH

MYD

Chevrolet

Silverado

2016 - 2018

All

All

L83

MYC

Chevrolet

Silverado New Model

2019

All

All

L82 L84

MYC

Chevrolet

Silverado 1500

2020

All

All

L82 L84

MYC

Chevrolet

Silverado 2500/3500

2016 - 2020

All

All

L8T, L96, LC8

MYD

Chevrolet

Suburban

2016 - 2020

All

All

L83

MYC

Chevrolet

Tahoe

2016 - 2020

All

All

L83

MYC

GMC

Savana

2016 - 2020

All

All

L20, L96, LC8, LGH

MYD

GMC

Sierra Models

2016 - 2018

All

All

L83

MYC

GMC

Sierra New Model

2019

All

All

L82 L84

MYC

GMC

Sierra 1500 Models

2020

All

All

L82 L84

MYC

GMC

Sierra 2500/3500

2016 - 2020

All

All

L8T, L96, LC8

MYD

GMC

Yukon Models

2016 - 2020

All

All

L83

MYC

Involved Region
North America and N.A. Export Regions.
or Country
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.
Condition
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.
Cause

Please refer to the following information to aid in addressing these types of conditions.

De nitions:
In general if there is insu cient engine ring 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 insu cient damping or TCC locking and releasing.
2. Chuggle: (often called boom) is induced from engine combustion exciting the driveline due to insu cient isolation.
Frequency of the boom is a ected by driveline mass, sti ness, damping, and gear.
3. Mis re: or knock is the engine having an irregular combustion event.
4. AFM Disturbances can be mislabeled as any of the de nitions above as well as shudder below, but in fact has to do
with the imbalance caused by less cylinders ring.
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 con rm the Disturbance Frequency and allow
the user to see if the disturbance tracks to engine speed (Chuggle, Mis re), 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 o 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
con rmed 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. Mis re – Can be viewed in GDS2 under engine control module and then selecting mis re data. This will prompt
a screen that will show mis re 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 con rm 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.
Perform TCC slip control test within this procedure.

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 identi ed 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 con rm TCC Shudder, Engine, Tire or Driveline
component related conditions.
Vibrations identi ed as shudder should be further investigated using the "Torque Converter Diagnosis" in SI as
a starting point.

An alternative diagnostic for TCC shudder is to road test the vehicle and monitor commanded and actual TCC
slip speeds.
Road test the vehicle under light throttle acceleration between 88 and 104 km/h (55 and 65 MPH) steady state
driving when the transmission is not actively shifting gears and monitor the following GDS2 parameters.

Callout 1
GDS2 data showing TCC slip peak to peak below 20 RPM is an example of normal TCC operation.

Callout 2
GDS2 data showing TCC slip peak to peak erratic near 0 RPM to over 100 RPM in a short time is an example of
a damaged torque converter clutch.

Callout 3
GDS2 data showing TCC slip peak to peak repeating near 60 RPM or less is an example of degraded uid.

Perform TCC slip control test within this procedure. Compare service tool collected data results to normal, damaged
and degraded operation.

TCC SLIP CONTROL
TEST RESULT

TCC rpm slip peak to peak

ACTION

Note

Normal (Callout 1)

Below 20 rpm.

Do nothing.

Damaged (Callout 2)

Near 0 to 100 rpm - erratic.

Inspect transmission further Inspect transmission pan magnet
for excessive metal accumulation.

Degraded (Callout 3)

Near 60 rpm - repeating.

Flush transmission uid.
Shudder, surge, sh bite likely.
Refer to bulletin 20-NA-142.

(at steady throttle)

Version History
Version

7

Modi ed

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.
01/17/2020 - Added the 2020 model year.
05/06/2020 - Added engine RPOs L82 and L84 and more diagnostic
information.
06/25/2020 - Added the 6L90 transmission RPO MYD. Added
Chevrolet Express and GMC Savana. Added engine RPOs L20, L96,
LC8 and LGH.
07/10/2020 - Added to refer to bulletin 20-NA-142 if diagnostics
leads to degraded fluid.

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