What is the difference between GM's second-generation 6AT and third-generation?

[VonIker]

GM's second-generation six-speed automatic transmission is prone to failure, while the third-generation is more reliable as it is an optimized and improved version. Transmission drawbacks: During acceleration, the transmission does not skip gears. The harder you press the accelerator, the more the transmission gears spin and slip. Sometimes there are difficulties in downshifting or upshifting. The shift piston wears out due to excessive impurities in the transmission fluid, preventing the transmission from depressurizing and thus making gear shifts impossible. Therefore, it is essential to change the transmission fluid regularly. There is also noticeable shift shock and jerkiness. Transmission advantages: The quality of Aisin transmissions is trustworthy. Typically, transmission issues arise not only from design and technical imperfections but also significantly from the owner's driving habits or prolonged driving under harsh road conditions. Therefore, it is reasonable to view transmission problems objectively, develop good driving habits, and adhere to regular maintenance and repairs as the proper approach.

[HarleyFitz]

The second-generation GM 6AT was commonly found in many older vehicles, such as the 2000s Chevrolet Impala. It always felt jerky during gear shifts, as if the engine was struggling—especially during low-speed acceleration or cold starts. The 'clunking' noise gave me a headache. The third generation, however, is a game-changer. I've driven it in newer models, and the shift logic is completely upgraded. With optimized software, shifts are now buttery smooth. Hardware-wise, the hydraulic system is more precise, better matched to modern turbocharged engines, and delivers an average 5-8% improvement in fuel efficiency, saving a lot on daily driving costs. Reduced weight and material improvements also mean fewer failures. Overall, the second gen feels more primitive, while the third gen is smarter and more efficient.

[KimberlyLee]

Having driven GM vehicles for many years, my impression of the second-generation 6AT was that it always felt a step slow, especially in traffic jams where frequent gear shifts made it shudder. Now, with the new third-generation SUV, everything is different: gear shifts are quick and silent, particularly at low speeds where it no longer jumps around, and it responds promptly when overtaking at high speeds. To my surprise, fuel consumption has also improved – previously, a full tank would last 400 kilometers, but now it easily exceeds 450. Maintenance costs are lower too, thanks to the improved durability of components, unlike the second generation which constantly threw up faults. GM really got it right this time with these improvements.

[DelAlexander]

Having worked on numerous GM transmissions, the second-generation 6AT commonly suffers from solenoid valve failures, leading to gearshift hesitation or oil leakage issues, which often require disassembly for repairs. The third generation is significantly different—with upgraded hydraulic units and control software, the failure rate has dropped, and cases of jerky shifts requiring rework are rare. Its transmission design is more lightweight, with longer maintenance intervals, making upkeep simpler and time-saving. GM has put effort into reliability, making the third generation overall more durable.