As the subject of how the FL2 and other 4x4 systems work keeps appearing in various threads I thought I would start this to provide a reference space.

Please share your knowledge or post links to information.

Link to video on Hadex on (Haldex gen5 - FL2 is earlier gen 3 or 4)
 FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

Haldex gen 4 FL2 - MY11 onwards

 FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

My CVT Outback is one of the smoothest , quietest , cars I’ve driven . In all scenarios where I’d take a car that I didn’t want to damage the AWD system has been excellent on road tyres .


 2009 GS Auto Zermatt Silver - Sold June 21 after 10 years of ownership

2016 Subaru Outback SE 2.0 diesel SE Premium Lineartronic Sold 2024 after 8 years and 80k miles . Best Car I ever owned !

2023 Toyota Hilux invincible X 2.8 Auto .

A site that references Land Rover and other 4x4 systems.

https://www.awdwiki.com/en/land+rover/ FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

A Brief History of Haldex

 FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

From the FL2 Repair Manual

Terrain response in 'Special Programs Off' mode as common with vehicles without terrain response, the coupling is programmed to transmit 500 Nm 369 lb ft of torque on Generation 3 couplings and 1500 Nm (1106 lb ft) of torque on Generation 4 couplings to the rear axle when the vehicle moves from rest in a straight line. This strategy minimizes traction loss from a standing-start regardless of the terrain. When the vehicle accelerates the pressure in the coupling is decreased to improve fuel economy.

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PRINCIPLES OF OPERATION
Generation 3 Couplings - up to 2009MY

An internal electronically-controlled pump provides hydraulic pre-charge pressure within the coupling. The pre-charge pressure supplies the required operating pressure to the clutch plates to eliminate initial wheel-spin as the vehicle accelerates from standstill.

In conjunction with the pre-charge pressure a mechanical hydraulic pump operates within the clutch plates to supply the coupling's main hydraulic operating pressure. The mechanical pump is functioned by the 'input' and 'output' of the coupling:
input - driveshaft connection from the front axle,
output - differential connection to the rear axle.

Any speed difference between the front and rear axles will start the operation of the mechanical hydraulic pump. The amount of hydraulic pressure applied to the clutch pack by the pump determines the gap between the clutch plates. For example, the greater the hydraulic pressure, the smaller the gap between the plates and subsequently the greater the torque transmitted through the coupling from the front axle to the rear axle.

This main hydraulic pressure is designed to transmit the torque for traction demands of off-road driving, and to provide lock-up as required.


Generation 4 Couplings - from 2009MY
The Generation 4 coupling still uses an electrically-controlled pump to provide hydraulic pre-charge to eliminate wheel-spin from standstill; however, the same pump is also used to provide the coupling's main hydraulic operating pressure.
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Mechanical Hydraulic Pump -Generation 3 Couplings - Vehicles up to 2009MY

The driveshaft is attached to the coupling's front clutch plate assembly (input), with the rear clutch plate assembly connected to the differential pinion (output). A swash-plate with 6 hydraulic rollers is also attached to the differential pinion. When there is no speed difference between the coupling's input and output, the rollers do not function.

However, when the front and rear axles start to rotate at different speeds, the swash-plate rotates relative to the rollers which generates the hydraulic pressure. This pressure is used to force the opposing clutch plates together, increasing the transmission of torque to the rear axle. As the difference in axle speed increases the hydraulic pressure pushes the clutch plates further together to increase the torque to the rear axle.

A control valve/axial solenoid controls the amount of pressure applied to the clutch plates, and hence the amount of torque transmitted to the rear wheels. Close manufacturing tolerances and exceptionally low component wear ensure torque control remains accurate throughout the vehicle's life.

Mechanical Hydraulic Pump - Generation 4 Couplings - Vehicles from 2009MY

The Generation 4 coupling does not use the swash plate to mechanically raise hydraulic pressure; instead, a new hydraulic pump is used to generate hydraulic pressure and force the clutch plates together. The removal of the swash plate allows a larger overall clutch plate surface area, which in turn reduces the hydraulic pressure requirement. The pressure required to achieve 1500Nm (1106 lb ft) has been reduced from 100 Bar for Generation 3 couplings to 40 Bar for Generation 4 couplings.
 FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

Resurrecting old thread

I found this handy little HALDEX error guide

https://www.haldexrepairs.co.uk/land-rover...solutions/ FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

that's a very useful site - cheers  Jules

Thanks for sharing...good info

IanMetro wrote:

From the FL2 Repair Manual
Terrain response in 'Special Programs Off' when the vehicle moves from rest
500 Nm (369 lb ft) of torque on Generation 3
1500 Nm (1106 lb ft) of torque on Generation 4

Before my FL2s, I had a large 2ltr turbo FWD estate. Even though it had traction control I had to be very careful from standstill/low speed, to gradually apply the throttle, otherwise I got embarrassing wheel spin.

One of the first things I noticed about my FL2 was that I could accelerate out of any road/lane even on a loose surface and quickly get to cruising speed, without any noticeably wheel slip or lose of directional control.

My FL2 seem very sure footed to drive, and everything is so well integrated that I don't seem to notice any traction/control intervention.

Well actually that's not quite true as I kicked off the anti roll intervention when I tried taking a large roundabout too fast when leaving a motorway. I experienced a strange floating sensation as the power was decreased and I think one of the rear brakes was gently applied. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)