The 166-series ON&OFFROAD package adds drivetrain hardware as well as driving programs. Mercedes-Benz Hong Kong’s 2012 M-Class release lists a two-stage transfer case with reduction gearing, an inter-axle differential lock and extended AIRMATIC functions as part of the optional package. Sources
Low range changes the gearing
The original X166 GL technical introduction specifies 1:1 high range and 2.93:1 low range in the optional transfer case. Low range provides greater mechanical reduction between the gearbox and the wheels: for a given transmission gear and engine speed, wheel speed falls and available drive torque increases. This differs from changing accelerator response or the automatic gearbox’s shift program. Sources
The W166 M-Class manual likewise describes LOW RANGE producing proportionately greater drive torque and roughly one-third of the high-range speed ratio. That is a separate function from selecting one of the package’s six driving programs. Sources
The centre lock and 4ETS work across different paths
The centre differential lock acts between the front and rear axles. The W166 manual describes the transfer-case differential lock balancing drive between those axles, while 4ETS controls traction between the two wheels on an axle through selective braking. Sources
The original X166 package uses a lockable centre differential and open front and rear differentials, supported by adapted 4ETS. The centre lock restricts front-to-rear speed differences mechanically; selective braking controls a spinning wheel on either axle. Sources
The program coordinates several systems
The original package offers AUTO, Offroad 1, Offroad 2, Sport, Snow and Trailer programs. They coordinate suspension height and damping, gearbox strategy, accelerator response, ESP functions and steering settings for the selected task. The package’s mechanical reduction remains a separate selectable function. Sources
Hong Kong names and model scope
The April 2012 Hong Kong M-Class release describes ON&OFFROAD as optional, alongside standard ML 350 4MATIC/4ETS, off-road mode and DSR downhill control. For the facelift X166, the March 2016 local GLS announcement calls the option Off-Road Engineering package: it adds OFF-ROAD+, low-range gearing and a centre differential lock beyond the ordinary DYNAMIC SELECT programs. The local manufacturer GLS release independently lists the same hardware. Sources
The separate ACTIVE CURVE SYSTEM option controls body roll through hydraulic anti-roll bars.
Sources
- Mercedes-Benz Hong Kong, A generation ahead: the new Mercedes-Benz M-Class, 13 April 2012, manufacturer-authored release preserved by 1888PressRelease: standard ML 350 off-road functions and optional six-program package with reduction gear, inter-axle lock and enhanced AIRMATIC.
- Daimler AG, Einführung neue GL-Klasse, Typenreihe X166, June 2012, order 6516 1394 00, printed p. 58 / viewer p. 59: lockable centre differential, open axle differentials, high/low ratios, adapted 4ETS and six programs. Manufacturer technical publication preserved by ManualsLib; original X166 scope.
- Mercedes-Benz, M-Class Operator’s Manual, 1665848681, Edition B 2013, as at 10 May 2012; printed pp. 243–250 / PDF pp. 245–252: program selection, vehicles with/without the package, front-to-rear differential-lock function, wheel-to-wheel 4ETS and LOW RANGE. North American operating documentation including country/order variations.
- Car1, Mercedes-Benz GLS 大型旅行車抵港開賣 $1,099,000 起, 14 March 2016, Hong Kong facelift GLS announcement: ordinary DYNAMIC SELECT versus optional OFF-ROAD+, low range and centre differential lock.
- Mercedes-Benz Hong Kong / Zung Fu, 全新平治GLS糅合平治GL與S系列–極致路面與越野表現, manufacturer release preserved by 28car; optional Off-Road Engineering hardware. Undated; no first-order or delivery date inferred.