Differential, rear, automatic locking, twin clutch all-wheel-drive system

Years 2016–20, 2025–27 Models 4 Factory citations 11

Also described as Axle, electronic positraction, twin-clutchAxle, electronic positractionAxle, rear, electronic, twin clutch

Also documented for Cadillac Chevrolet GMC

Documented applications

Enclave — C1XX (2018–2024)

2018–2020 Factory-verified

only in: AWD; Premium, Avenir: S; 2019–2020: GM Authority (Premium and Avenir AWD from 2018 to 2020); GM Authority reports it listed for 2021 Essence, Premium and Avenir AWD, then dropped, leaving 2021 with the regular AWD system only

GM factory document — 2018 buick enclave fleet order guide wayback, p.1.

Envision — D2XX, imported from China (2016–2020)

2016–2019 Factory-verified

1SN, 1SP: S

GM factory document — 2016 buick envision order guide copy gm authority, p.4, p.16.
GM factory document — 2017 buick envision order guide copy gm authority, p.6, p.20.
GM factory document — 2018 buick envision order guide copy gm authority, p.5, p.19.
GM factory document — 2019 buick envision order guide copy gm authority, p.6, p.22.

Envision — E2XX (2021–2027)

2025–2027 Factory-verified

2027: all trims: S; the full guide adds twin-clutch

GM factory document — 2025 buick envision fleet order guide rpo codes, p.1.
GM factory document — 2027 buick envision fleet order guide rpo codes, p.1.
GM factory document — 2027 buick envision fleet order guide, p.7.

Regal — E2XX (2018–2020)

2018–2019 Factory-verified

2019: Preferred II, Essence, GS: S (2019 Sportback order guide)

GM factory document — 2018 buick regal sportback fleet order guide wayback, p.1, p.5.
GM factory document — 2018 buick regal tourx fleet order guide wayback, p.1.
GM factory document — 2019 buick regal sportback order guide copy gm authority, p.7.

This page aggregates every documented appearance of G99 in the Buick reference. Confidence and citations are shown per application — the same code can be better documented in one year than another.