Transmission seems to “stutter” at 20-25 ph and 40-45 ph
If I had to guess I would say that the transmission was serviced with the wrong type of transmission fluid. They do sell a corrective additive called Shudder Fix. However the better course of action would be to have the transmission fluid replaced with the correct type. There is a TSB – Technical Service Bulletin out on this issue.
TSB# 16-NA-175
TSB 16-NA-175 Description
Shake and/or shudder during light acceleration between 25 and 80 MPH at a steady state. (June5, 2018)
Condition
Some customers may comment on any of the following conditions:
- A shake and or shudder during light acceleration between 25 and 80 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.
- Shudder feeling is evident in both Drive and M7 MY15-16 &L7 MY17 and MY18 Mode.
Diagnosis Instructions
To ensure TCC Shudder is diagnosed correctly, please drive the following schedule on a smooth road with transmission sump temperature between
122°F (50°C) – 158°F (70°C).
Important: For some road conditions, it may be required to apply the brake pedal and throttle simultaneously to stay within desired gear, engine
firing mode, engine torque range, and engine/vehicle speed ranges.
For Full Size Trucks/SUVs– Press and hold the tow-haul mode button for 5 seconds to disable grade braking to prevent downshifts during test.
Run the following tests for 3 operational modes:
A. Normal Operation (GDS2 for viewing only).
B. GDS2 Commanding TCC in Disabled Operation. (TCC Open).
C. GDS2 Commanding TCC in Enabled Operation. (TCC Locked).
To confirm TCC Shudder, the vibration concern must be created in normal operation (Mode A) of the test.
If the concern is gone with the torque converter clutch disabled (Mode B, TCC Open) and is gone with torque converter clutch enabled (Mode C, TCC Locked), then the vibration root cause is TCC Shudder, and the fluid flush procedure corrective action described below should be performed.
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 enabled (Mode C, TCC slip speed at zero), then the vibration root cause is NOT TCC Shudder.
Vibrations not identified as TCC Shudder should be further investigated using the Vehicle Vibration Diagnosis in SI as a starting point.
Service Procedure
Important:
Requires Mobil 1 Synthetic LV ATF DEXRON HP transmission fluid.
Note: U.S. dealers must order the Mobil 1 Synthetic LV ATF DEXRON HP
fluid through your local General Motors oil distributor. When contacting
the General Motors oil distributor request Mobil 1 Synthetic LV ATF DEXRON HP.
Canadian dealers must order part number 19355657 through Kem Krest Canada.
1. Drain, Clean pan/magnet, Replace Filter, Oil Fill, & Remove fluid from the oil cooler lines.
◦ A.) Use filtered compressed air regulated to 60 psi to remove transmission fluid from the transmission oil cooler lines.
◦ B.) Remove the transmission fluid pan and drain transmission fluid following SI procedures for the application you’re working on. Discard
all oil.
Note: If you find that the fluid is cloudy, milky, or appears to be contaminated with water or engine coolant, DO NOT proceed with below steps. Follow Both SI Procedures for “Cooling System Leak Testing” and “Engine Coolant/Water in Transmission.”
◦ C.) Clean the pan/magnet if any metallic particles present and replace transmission filter.
Install the transmission fluid pan and refill with new Mobil 1 Synthetic LV ATF DEXRON HP transmission fluid following the Fluid Fill Procedure in SI
to obtain correct fluid level. The shudder should be improved after the completionof this flush procedure.
Note: Shudder should improve directionally right away, but for full affect, the vehicle may need to be driven up to 200 miles (322 km) and a minimum of two cold to hot drive cycles before determining if the fluid flush corrected the condition or not. Do not re-evaluate vehicle for additional customer shudder concerns until the vehicle has been driven 200 miles (322 km).