GM 6T40 / 6T45 common fault codes

6T40 / 6T45 is a 6-speed automatic transmission that belongs to General Motors' 6T series. It is designed for front- and all-wheel-drive systems, particularly in compact and midsize passenger cars. The transmission has been used in models such as Chevrolet, Buick, GMC and Opel / Vauxhall. Common issues include clutch drum failure and TCM faults.

If the transmission fluid has not been changed since factory delivery, we recommend to change oils with flush method.

 

Things to consider during repairs

  • Fluid level: Make sure the transmission fluid level is correct. Overfilling can cause overheating and other problems.
  • Sensors and wiring: Check the condition of sensors and their wiring. Faulty sensors can cause multiple error codes.
  • Solenoids: Solenoid malfunctions are common. Check their operation and replace if needed.
  • Software updates: In some cases, a TCM software update may solve the issue. Check the manufacturer's recommendations.

P0218 – Transmission Fluid Over Temperature

  • Symptoms: Transmission overheating, possible fault mode during driving.
  • Cause: The most common cause is fluid overfill, which prevents proper cooling.
  • Fix: Check and adjust the fluid level to the correct amount. Ensure that the temperature-regulated fluid level control valve works correctly.
     

P0711 / P0712 / P0713 – Transmission Fluid Temperature Sensor

  • Symptoms: Transmission malfunction, such as erratic shifting.
  • Cause: Faulty temperature sensor or its wiring.
  • Fix: Replace the control module.
     

P0716 / P0717 – Input Speed Sensor

  • Symptoms: Transmission slipping, erratic shifting.
  • Cause: Faulty input speed sensor or its wiring.
  • Fix: Inspect and replace the input speed sensor if necessary. Check the condition of the wiring.
     

P0741 – Torque Converter Clutch (TCC) System Stuck Off

  • Symptoms: Increased fuel consumption, transmission overheating.
  • Cause: Faulty TCC solenoid or mechanical fault in the torque converter.
  • Fix: Check or replace the valve body. Check or replace the torque converter.
     

P0776 – Pressure Control Solenoid B Performance

  • Symptoms: Harsh shifting, transmission slipping.
  • Cause: Faulty pressure control solenoid or mechanical issue in the transmission.
  • Fix: Check the fluid level. Inspect the control module and valve body and replace if necessary. Check the mechanical condition of the transmission, especially the 3-5-R clutch drum.