ABS braking moment control circuit, function

ABS control module (N47-7)

Voltage supply,

terminal 87,

overvoltage protection relay,

front passenger-side fuse and relay module

(K1, K40, K40/4)

Data link connector (X11/4)

ABS hydraulic unit (A7/3)

Return pump (A7/3m1)

Solenoid valves

(A7/3y6 to A7/3y21)

Return pump relay

(K20/1, N65k4, K40/2k4)

Left front wheel speed sensor (L6/1)

Right front wheel speed sensor (L6/2)

Rear axle speed sensor (L6)

Stop lamp switch

(S9/1)

Ground

(W16, W16/4, W29/2)

CAN data bus

Instrument cluster (A1)

ABS MIL (A1e17)

HFM, ME, EVE, ERE, CRD control module (N3/4, N3/10, N3/7, N3/8, N3/9)

The corresponding functions in the ABS hydraulic unit (A7/3) are controlled by the electrical/electronic components.

On model 202 up to 07/96 the ABS control module (N47-7) is supplied with voltage via the overvoltage protection relay (K1). On model 202 as of 08/96, model 208 and model 170 the voltage is supplied via the relay module (K40 or K40/4).

The ABS control module (N47-7) receives input signals from the following components:

 3 rpm sensors
 Stop lamp switch

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The input signals are processed into output signals in the ABS control module for the following components:

 Solenoid valves
 Return pump (via relay)

 ABS MIL (actuation - direct, serial or via CAN data bus)

Based on the input signals, the ABS control module (N47-7) decides which of the four operating modes

 Normal mode
 ABS control mode, pressure build-up
 ABS control mode, hold pressure
 ABS control mode, pressure reduction

are to be iniated.

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Normal mode

In this case there are no differences in speed (which necessitate a control mode). All the solenoid valves in the ABS hydraulic unit (A7-3) are de-energized.
The system is ready for braking.
This operating mode is also set when there is a fault in the ABS.

ABS control mode

The ABS control module (N47-7) recognizes from the wheel speed signals that the conditions for ABS control exist.

The corresponding solenoid valves are actuated by the ABS circuits in the ABS control module (N47-7).

The left or right front axle solenoid valves in the ABS hydraulic unit (A7-3) are actuated separately.

The solenoid valves for the rear axle act together on both rear wheels for the ABS control process. If an ABS control process is effective, a rapid change in pressure between pressure build-up, hold pressure and pressure reduction takes place at the wheel brakes.

This ABS control process can be felt via a pulsating brake pedal.