For 1990-2009 cars

### Components

The all-wheel drive system consists of 5 main components:

• | transfer case

• | propeller shaft

• | differential clutch

• | limited slip differential

• | rear differential clutch control module

#### Transfer Case

The transfer case is located to the right of the gearbox, to which it is bolted. Its function is to take power from the gearbox and transfer it via a hypoid gear and a propeller shaft to the differential clutch.

#### Differential Clutch

The function of the differential clutch is to control the torque to the rear wheels. It can be varied between 0-100% drive via a hydraulically controlled multi-disc clutch. The differential clutch is bolted to the limited slip differential with 4 bolts.

#### Propeller Shaft

The function of the propeller shaft is to transfer power from the transfer case to the differential clutch.

#### Limited Slip Differential

The limited slip differential, also called rear drive module, is located in the subframe and the drive shafts extend from it to each rear wheel. The limited slip differential consists of a hypoid gear and a differential. The limited slip differential is fully mechanical. The limited slip differential clutch, if installed, is bolted with 6 bolts to the left-hand side of the limited slip differential. Its function is to fully or partly lock the left-hand drive shaft to the differential housing. When this takes place the drive torque can be distributed between the rear wheels. The limited slip differential clutch is a disc type, and it is electro-hydraulically controlled by the rear differential clutch control module via a pressure control valve which is fitted on the limited slip differential clutch housing. The rear differential clutch control module calculates drive torque distribution. There are two variants: with and without limited slip differential clutch for the rear wheels.

#### Hydraulic Pump

The hydraulic pump consists of an electric motor and a pump housing. It is supplied with power from the rear differential clutch control module. The motor drives a five cylinder axial piston pump in the pump housing which produces an operating pressure of 2700-3200 kPa (392-464 PSI). The pressure control valve is electrically controlled and its function is to regulate the hydraulic pressure (0-3000 kPa (435 PSI)) to the operating piston. It is directly connected to the rear differential clutch control module which supplies it with a pulse width modulated voltage. The rear differential control module activates the output to the hydraulic pump as soon as the following conditions are fulfilled: "ignition ON" and "engine started". The output is active until the calculated pressure is approx. 3200 kPa (464 PSI). The pressure is calculated by means of the rear differential control module measuring the electric motor's power consumption. The higher the pressure, the greater the resistance is for the electric motor to drive the pump itself, and the higher the current becomes. When the system pressure is approx. 3200 kPa (464 PSI) (fully charged accumulator) the accumulator piston exposes the unloading holes and the pressure does not increase further. The current to the motor does not increase any further but remains constant. The maximum system pressure is reached, the rear differential control module shuts down the pump. Restart takes place when the calculated pressure is below approx. 2700 kPa (392 PSI).

#### Rear Differential Clutch Control Module

The rear differential clutch control module is fitted on the housing. The hydraulic pressure is built up by an electrically driven pump, and is controlled by the rear differential clutch control module via a solenoid valve. By using information on the bus the rear differential clutch control module calculates the drive torque distribution between front and rear axles as well as the distribution between the rear wheels for cars with limited slip differential clutch. The rear differential clutch control module is connected to the vehicle's communication bus. The bus messages are used to determine the operating/driving conditions for the vehicle, and accordingly how much drive torque should be transferred to the rear wheels. The rear differential clutch control module and the control valve are calibrated together, they must be replaced together without exception.

The rear differential clutch control module has a monitoring for the bus communication, inputs, outputs, certain mechanical faults and internal control module faults. If relevant control module functions are missing or other mechanical or electrical faults are recognized diagnostic trouble codes are generated.

• | Internal signals

⇒ | The control module has a monitoring for internal control module faults.

• | Input signals

⇒ | The control module has an input for an internal temperature sensor. The temperature sensor is fitted on the rear differential control module's circuit board and is monitored for electrical faults. The temperature sensor is also used by the rear differential control module to calculate the current fluid and disc pack temperature in the differential clutch.

• | Output signals

⇒ | The control module has pressure control valve outputs for differential clutch and limited slip differential clutch (if fitted) respectively, as well as for the pump motor. These are monitored for electrical faults.

• | Mechanical functions

⇒ | The control module can diagnose clogged pressure control valves and leaking check valves.