Audi Workshop Service and Repair Manuals

ABS with EDL/ASR/ESP control unit -J104

The control unit is combined with the hydraulic unit to form an assembly. It regulates the ESP, ABS, EDL, ASR, EBPD and overrun torque limiting functions. A control unit self-test is implemented when the ignition is switched on. All electrical connections are permanently monitored and the function of the solenoid valves periodically checked. In the event of total control unit failure, only the normal brake system is available.

Steering angle sender -G85

The steering angle sender is located in a joint housing together with the airbag coil connector. It is located on the steering column between steering column switch and steering wheel. The steering wheel angle is transmitted via the CAN bus to the control unit for ABS/ASR/ESP
-J104. Zero position compensation must be performed following replacement of control unit or sender. There is no ESP function if the sender is defective.

Lateral acceleration sender -G200

The lateral acceleration sender transmits the cornering force values to the control unit for ABS/ASR/ESP -J104. Zero position compensation must be performed following replacement of control unit or sender. There is no ESP function if the sender is defective.

Yaw rate sender -G202

The yaw rate sender records data on so-called yaw moments or yaw rates which attempt to rotate the vehicle about its vertical axis and transmits these values to the control unit for ABS/ASR/ESP -J104. There is no ESP function if the sender is defective.

Brake pressure senders -G201 and -G214

The brake pressure sender records the instantaneous brake pressure in the brake circuit and transmits it to the ABS with EDL control unit -J104. The control unit uses this information to calculate the wheel braking forces and thus the longitudinal forces acting on the vehicle. Dual brake pressure senders are fitted to provide maximum reliability. There is no ESP function even if just one sender fails. The senders are located at the brake servo.

Brake pressure solenoid valve, in brake servo -N247

If the system recognises the need for ESP action and the driver has yet to press the brake pedal, the brake pressure solenoid valve is actuated by the ABS with EDL control unit -J104. This causes the brake servo to build up a pressure of approx.10 bar and the brake system is activated.

Button and lamp for ASR

Only the ASR function can be deactivated/activated by way of the button. ASR deactivation is possible at vehicle speeds of up to 50 km/h. The ASR function is activated automatically at speeds in excess of 70 km/h. ASR deactivation causes the ASR/ESP lamp to light. The ASR/ESP lamp flashes in the event of ASR/ESP action. The lamp is permanently lit if there is no control unit power supply, the control unit has been unplugged or the button pressed. It is appropriate to deactivate the ASR/ESP function when trying to drive off in deep snow or on soft ground, when using snow chains and when checking the vehicle on a dynamometer.

Brake detection switch, ESP -F83

The brake detection switch acts as a changeover switch. When the driver presses the brake, the switch changes from signal contact 1 to signal contact 2. As there is only ever one signal contact made, the system can clearly recognise the instantaneous state and the switch thus offers a high level of intrinsic safety.

Active brake servo with tandem master cylinder

The active brake servo or booster builds up pressure in the event of ESP action. This is necessary, as the return pump intake is not always sufficient to generate the pressure required on account of the high brake fluid viscosity at low temperatures.

EBPD

The brake system is split diagonally into two hydraulic circuits, one for supplying the front left and rear right brakes and the other for supplying the front right and rear left brakes.