16-NA-182: DTC P0777, Firm 3–2 Downshifts (Reprogram TCM) – 2016 Chevrolet & GMC

#16-NA-182: DTC P0777, Firm 3–2 Downshifts (Reprogram TCM) – (Jun 7, 2016)

Subject: DTC P0777, Firm 3-2 Downshifts (Reprogram TCM)

Brand: Model: Model Year: VIN: Engine: Transmission:
from to from to
Chevrolet Express 2016 2016 Equipped with 6.0L Engine (RPO L96) Equipped with 6L90 Automatic Transmission (RPO MYD)
Chevrolet Silverado 2500/3500
GMC Savana
GMC Sierra 2500/3500


Involved Region or Country North America
Condition Some customers may comment on an illuminated MIL. Technicians may find DTC P0777 as an active or a history DTC. This concern will typically occur in cold ambient temperatures of -5 to +5°C (23 to 41°F).

Drivers of Silverado or Sierra models may also comment on a firm 3-2 downshift at light or heavy throttle, typically below 25°C (77°F) transmission temperature. This firm downshift does not affect Express or Savana models.

Cause This condition may be due to a software anomaly.



A revised calibration has been developed to address these concerns. Update the transmission control module (TCM) using the Service Programming System (SPS) with the latest software available on TIS2WEB.


  • DO NOT program a control module unless directed to by a service procedure or a service bulletin. If the control module is not properly configured with the correct calibration software, the control module will not control all of the vehicle features properly.
  • Ensure the programming tool is equipped with the latest software and is securely connected to the data link connector. If there is an interruption during programming, programming failure or control module damage may occur.
  • Stable battery voltage is critical during programming. Any fluctuation, spiking, over voltage or loss of voltage will interrupt programming. When required, install the EL-49642 SPS Programming Support Tool to maintain system voltage. If not available, connect a fully charged 12 V jumper or booster pack disconnected from the AC voltage supply. DO NOT connect a battery charger.
  • Turn OFF or disable systems that may put a load on the vehicles battery such as; interior lights, exterior lights (including daytime running lights), HVAC, radio, etc.
  • During the programming procedure, follow the SPS prompts for the correct ignition switch position.
  • Clear DTCs after programming is complete. Clearing powertrain DTCs will set the Inspection/Maintenance (I/M) system status indicators to NO.


Service Procedure

Refer to Control Solenoid Valve and Transmission Control Module Assembly Programming and Setup in SI.


Warranty Information

For vehicles repaired under the Bumper-to-Bumper coverage (Canada Base Warranty coverage), use the following labor operation. Reference the Applicable Warranties section of Investigate Vehicle History (IVH) for coverage information.

Labor Operation Description Labor Time
2810155 Control Solenoid Valve and Transmission Control Module Assembly Reprogramming with SPS Use Published Labor Operation Time


Version 1

June, 2016



Download (PDF, 661KB)


GM Diagnostic/Programming (TIS2Web)

Approved J2534 Device with TIS2WEB can reprogram 1996 and later All GM Modules.

To obtain the latest electronic controller calibration information for your vehicle, go to https://tis2web.service.gm.com/tis2web and enter the vehicle’s 17 character Vehicle Identification Number (VIN) and select ‘Get CAL ID’.

You can then compare the latest part number with the actual number installed on the vehicle to determine if a reprogram is needed.

The Service Programming System (SPS) application is part of the TIS2Web system. To program an ECU, the SPS application must communicate with the vehicle control modules using the proper J2534 programming interface tool.

The following are the supported interface tools:

OEM GM Tech 2 Dealer Package
Bosch GM MDI 2 (2nd Gen) MDI2 interface
Drew Tech CarDaq-Plus 2 SAE J2534-1/2 Reflash Reprogramming Tool OEM Diagnostics
Drew Technologies (DRWCDPLUSKIT) CarDAQ-Plus J2534 Flash Reprogramming Kit
Drew Tech CarDaq-M 2 SAE J2534-1/2 Reflash Reprogramming Tool OEM Diagnostics

Drew Technologies (DRWMONGGM) Mongoose GM Vehicle Interface (VPW/CAN) J2534

VSI J2534 ECU Reprogrammer & Diagnostic Adapter
Autel (AULMF2534) MaxiFlash Pro
Dearborn d-Bridge Adapter J2534 OBDII Engineering Tool

The Tech 2 supports model years 1996 and beyond. With the addition of the CAN Diagnostic Interface (CANdi) module, Tech 2 is fully backward compatible with current Tech 2 functionality and operates transparently when diagnosing non-CAN-equipped vehicles.

Servicing the next generation Global A vehicles will require the diagnostic software, GDS2, Global Diagnostic System 2 running on a local PC device while the MDI is connected to the vehicle.

The GM MDI is the Global Diagnostic tool for future vehicles starting with Global A vehicles. The GM MDI was introduced in the fall of 2007 for Pass-Thru programming and offers faster programming speed. It can be used to perform Pass-Thru programming on all vehicles built since 1996 and into the future. Click here to view a list of GDS supported vehicles.



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