ETS braking moment control circuit, function

CAN data bus

ETS/SPS control module (N47-2)

ASR/ETS/ESP hydraulic unit (A7/3)

High-pressure/return pump (A7/3m1)

Solenoid valves (A7/3y6 to A7/3y27)

Front left speed sensor (L6/1)

Right front axle VSS sensor (L6/2)

Left rear axle VSS sensor (L6/3)

Right rear axle VSS sensor (L6/4)

Data link connector (DTC readout) (X11/4)

Instrument cluster (A1)

ABS MIL (A1e17)

ETS warning lamp (A1e36)

ETS MIL (A1e35)

Low brake fluid level/parking brake/brake booster pressure indicator lamp (A1e7)

Warning buzzer (A1h1)

Engine control module (ME-SFI) (N3/10), transmission control module (N15/3), transfer case control module (N78)

High-pressure/return pump relay (F1k25)

Fuse and relay module (F1)

Fuse (F1f22)
Terminal 15
Fuse (F1f27)
Terminal 30

Ground
terminal 31

Stop lamp switch (4-pin) (S9/1)

Brake fluid level switch (S11)

The corresponding functions in the ASR/ETS/ESP hydraulic unit (A7/3) are controlled with the components of the electrical/electronic system.

The voltage of the ETS/SPS control module (N47-2) is supplied via the fuse and relay module (F1), fuse (f22) terminal 15 and fuse (f27) terminal 30.

The ETS control module receives input signals from the following components for the ETS and ABS function:

 4 speed sensors

 Stop lamp switch

 Brake fluid level switch

 CAN messages from the control module: ME-SFI, ETC, transfer case and instrument cluster

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In the ETS control module the input signals are conditioned into output signals for the following components:

 Solenoid valves

 Self-priming high-pressure/return pump (via relay)

 ETS warning lamp

 ABS MIL

 ETS MIL

 Low brake fluid level/parking brake/brake booster pressure indicator lamp

 Warning buzzer

Based on the input signals the ETS control module decides which of the 4 operating modes

 Normal mode

 ABS control mode

 Electronic brake booster pressure

 ETS control mode

has to be engaged.

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Normal mode

In this case there are no speed differences (which require a control mode). All solenoid valves in the ASR/ETS/ESP hydraulic unit (A7/3) are in the basic position, i.e. de-energized. This system is ready for braking.
This type of operation also applies if ETS and ABS switch to fault.

ABS control mode

The ETS/SPS control module (N47-2) recognizes from the speed signals that the criteria for ABS control exists. The appropriate solenoid valves are actuated by the ABS circuits in the ETS/SPS control module (N47-2).

The left and right front axle solenoid valves in the ASR/ETS/ESP hydraulic unit (A7/3) are actuated separately (individual control).

The solenoid valves for rear axle on the left or right are actuated together for the ABS control process.

 ABS function when off-road gear is engaged (LOW RANGE)

When the conditions (V<30 km/h and rough road recognition) are met, the increased tendency of the front wheels to lock is permitted by the ABS. This results in shorter stopping distances on loose ground off-road.

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Electronic brake booster pressure

The slip of the rear wheels is monitored sensitively using the wheel speeds each time the vehicle is braked. The permissible rear axle slip values are prevented from being exceeded by actuating the appropriate solenoid valves in the hydraulic unit.

ETS control mode

It is absolutely essential for the driver to operate the accelerator pedal for the ETS control mode to function.

The speed signals are continuously processed in the ETS/SPS control module (N47-2).

As soon as a drive wheel tends to spin, the ETS/SPS control module (N47-2) actuates the self-priming high-pressure/return pump (A7/3m1), the appropriate switchover solenoid valve (A7/3y24 or A7/3y25) and inlet solenoid valve (A7/3y26 or A7/3y27) of pressure circuit 1 or 2 and the appropriate solenoid valves for the wheel brakes.

The ETS control mode is interrupted by operating the brake pedal. If the driver stops operating the brake pedal, ETS control mode is also switched off.

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