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X166 GL / GLS: engineering

Seat linkages, load-adapted ESP, camera synthesis and off-road lighting in the seven-seat X166, with Hong Kong GL and GLS milestones.

X166 covers the second-generation GL and its facelift, renamed GLS. The name change did not create a new chassis generation. The five-seat W166 ML / GLE is a separate body in the same 166 family. Sources

A cushion that moves as the backrest folds

The third row has two individual seats that fold electrically into the load area. Under each seat, a four-bar linkage supports the cushion, while connecting rods link it to the pivoting backrest. As the backrest folds, the cushion moves down and forwards. The backrest surfaces and two additional covers then form a nearly level load floor, without removing the seats. Each seat has separate electric drives for locking/unlocking and folding. Sources

Two upright third-row seats in a facelift X166 GLS, viewed through the open rear passenger door
Third-row seats in a facelift X166 GLS at the 2017 Frankfurt motor show, with the backrests upright and access space visible. Photo: Matti Blume, Wikimedia Commons original, CC BY-SA 4.0 International. Resized and recompressed, not cropped; image remains under the same licence.

EASY-ENTRY makes an access opening in the second row. In the original optional electric version, actuators release a spring-preloaded movement: the head restraint retracts, the backrest folds onto the cushion and the whole outer seat tips forwards. The owner’s manual specifies a manual return to its original position. This is a different mechanism from lowering the third row into the floor. Sources

Mercedes-Benz Hong Kong’s May 2013 GL release described electric third-row operation as standard and electric EASY-ENTRY as optional. Its April 2014 GL 63 AMG release listed electric EASY-ENTRY as standard on that model. Sources

With the third row folded, the original GL provided 680 litres behind the second row, measured up to its backrest height. Sources

ESP takes the load into account

The original GL’s load-recognition system adapted ESP intervention thresholds to the vehicle’s actual load situation. That is a control adjustment beyond AIRMATIC keeping the body level: the stability system changes its thresholds as the load changes. The 2012 technical introduction lists air-suspension load recognition for ECE-market cars and excludes the USA; Hong Kong’s April 2013 GL announcement also names ESP load recognition. Sources

Hydraulic torque at the anti-roll bars

The optional ACTIVE CURVE SYSTEM uses front and rear active anti-roll bars with two hydraulic rotary actuators. Its control unit adjusts hydraulic pressure using lateral acceleration as a principal input, so the bars apply controlled torque to oppose body roll in bends. AIRMATIC’s air springs continue to support and level the vehicle. See how ACTIVE CURVE SYSTEM works. Sources

Low range changes the mechanical reduction

The original GL’s optional ON&OFFROAD package adds a transfer case with 1:1 high range and 2.93:1 low range. The extra reduction increases drive torque and lowers wheel speed for a given gearbox ratio. Its centre differential lock acts between the axles; front and rear axle differentials remain open, with 4ETS using selective braking to control wheel traction. The ON&OFFROAD explanation follows those separate functions. Availability varies by model and phase. Sources

Rear cooling has its own hardware

The original international equipment description offered an additional rear air-conditioning system alongside three-zone THERMOTRONIC. It placed an extra evaporator in the left rear of the body to cool the third row. Temperature and blower settings for that row followed the second-row settings, giving the third row its own cooling hardware within the existing rear control zone. Sources

Four cameras create the overhead view

The optional 360° camera combines images from a camera in the grille, one in the tailgate and one in each exterior mirror. A control unit assembles those four views into a virtual viewpoint above the vehicle, so the driver can see its edges and immediate surroundings on COMAND. The overhead view is calculated from the installed cameras. Sources

A May 2013 Hong Kong GL 500 test described switching between camera views to help with parking and inspecting rough ground. Mercedes-Benz Hong Kong listed the system as optional. The manual also identifies areas the cameras cannot show, including under the front and rear bumpers and very close to either bumper. Sources

Four cameras at the grille, tailgate and two exterior mirrors feed a control unit that calculates a virtual overhead view
Conceptual schematic of the original X166's optional 360° camera: a control unit combines four camera images into a virtual overhead view. Not to scale. Original illustration: Siu's MB Trivia, original SVG, CC BY 4.0. Sources

Off-road lighting spreads the beam

The original X166’s optional off-road lighting changed the headlamps’ physical beam pattern. With the relevant ON&OFFROAD equipment, selecting Off-Road 1 or Off-Road 2 pivoted the bi-xenon modules 6° outwards, producing a wider, symmetrical dipped beam; the LED cornering lamps stayed on. This illuminated more of the ground to either side during low-speed manoeuvres. Sources

The original GL manual limits this lighting function to 50 km/h or below and describes the cornering lamps remaining active while the active bend-light function is suspended. Mercedes-Benz Hong Kong’s May 2013 release also offered bi-xenon Intelligent Light System headlamps with the new off-road light. Sources

STEER CONTROL gives a steering cue

STEER CONTROL applies a noticeable force at the steering wheel in the direction that helps stabilise the vehicle. The original GL manual describes two examples: braking when the wheels on one side are on a wet or slippery surface, and a vehicle beginning to skid. The driver feels a corrective steering cue and remains responsible for steering. Mercedes-Benz Hong Kong included the system in its original GL equipment description. Sources

An ESP fault removes STEER CONTROL’s corrective cue, while ordinary power steering continues to work. Sources

Crosswind Assist acts through the brakes

The original GL’s Crosswind Assist uses targeted brake applications to counter a gust’s effect on the vehicle’s course. Integrated into ESP, it responds according to the wind’s direction and intensity. Mercedes-Benz Hong Kong listed Crosswind Assist as standard in May 2013. Sources

The original German-market manual describes operation above 80 km/h, on straight roads or gentle bends, with ESP available and switched on. Sources

Hong Kong: GL becomes GLS

Silver pre-facelift X166 GL 500 4MATIC, seen from the front quarter
Pre-facelift X166 GL 500 4MATIC photographed in Düsseldorf in June 2014. Photo © M 93, Wikimedia Commons original, CC BY-SA 3.0 Germany. Resized and recompressed, not cropped; image remains under the same licence.
Date Documented local milestone Sources
April 2013 A report on 20 April stated that the GL 500 was on sale in Hong Kong, from HK$1,384,000. Mercedes-Benz Hong Kong’s 10 May release also listed the model.
April 2014 The manufacturer’s 10 April Hong Kong release listed the GL 63 AMG 4MATIC at HK$2,268,000.
March 2016 The 14 March local GLS announcement named GLS 400, GLS 500 and Mercedes-AMG GLS 63. The first two used 9G-TRONIC; the AMG retained AMG SPEEDSHIFT PLUS 7G-TRONIC.
Grey facelift X166 GLS 500 4MATIC with revised headlamps and grille, seen from the front quarter
Grey facelift X166 GLS 500 4MATIC photographed in May 2026, for comparison with the earlier GL front styling. Photo: Ethan Llamas, Wikimedia Commons original, CC BY-SA 4.0 International. Resized and recompressed, not cropped; image remains under the same licence.

The GL made its world premiere in New York in April 2012, a year before the Hong Kong GL 500 on-sale report above. Sources

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