Loss of Forward Gear on CVT Transmission

Some 2019-2024 Malibu; 2020-2024 Encore GX; and 2021-2024 Trailblazer models equipped with the VT40 CVT transmission (RPO MRG) may have a loss of forward gear or slipping condition. DTC P2714 (Transmission Control Solenoid Valve 4 Stuck Off) also may be set in the Transmission Control Module (TCM).

The intermittent transmission gear condition may be due to the clutch regulator valve sticking in the valve body, damage to the forward clutch piston (Fig. 5) and/or wear in the primary pulley bearing bore.

 

Fig. 5

 

TIP: Before making any repairs, refer to Bulletin #20-NA-120. If the transmission chain and sheaves are damaged, transmission replacement will be needed and no other repairs should be performed. The condition of the chain and sheaves can be checked using a borescope. Borescope SRV3880LNR, available to U.S. dealerships through the GM Loan Tool Program, or equivalent should be used for inspection. The borescope needs to be one that can be articulated.

Begin diagnosis by verifying DTC P2714 is set, and that the transmission fluid is at the proper level. Refer to Service Information document #4818020. The transmission fluid temperature must be between 140°–176°F (60°–80°C) to properly check the fluid level.

If the fluid level is correct, and the transmission is at operating temperature, drive the vehicle and verify if there is a slip or lack of engagement in Drive.

If there is no slip in Drive, clear the DTCs and test drive the vehicle again, ensuring the transmission is at operating temperature. If the DTC does not immediately reset, and there is no slip condition or loss of drive felt, perform 3 to 4 WOT accelerations.

If the DTC does not reset after the WOT accelerations, replace the valve body (not the solenoid valve body) and reevaluate.

If DTC P2714 resets, check to see if there is no forward motion, but there is Reverse; a slip under heavy acceleration; the DTC or concern is repeatable; there is a drop in primary and secondary pulley pressure due to a leak; or the primary and secondary pulley pressure drops during an Auto Stop. Pressure during an Auto Stop should be around 400 kPa. If the pressure is below 300 kPa, it may indicate that there a piston seal leak.

If there is a loss of Drive or slipping, the fluid has a burnt odor or any of the above indicators are present, the transmission should be disassembled and the forward clutch piston inspected for damage along the side.

If the forward clutches are worn and the forward clutch piston is damaged, replace the forward clutch piston, the housing and the applicable apply components as needed.

If the forward clutch piston is not damaged, check the pump for signs of wear. (Fig. 6)

 

Fig. 6

 

Signs of wear indicate the primary pulley bearing has spun in the bore, allowing the turbine shaft to become off-center. (Fig. 7) When this happens, it causes a pressure leak. If this condition is found, the transmission will need to be replaced.

 

Fig. 7

 

TIP: The primary pulley bearing is installed inside the case on the primary pulley, which cannot be accessed for inspection. Inspection of the pump for DTC P2714 and no concern found with the forward clutch piston, is critical to a proper diagnosis.

Refer to Bulletin #24-NA-009 for more information and part numbers.

Thanks to Marty Leach