Function of ETS control module - GF42.35-P-4500-01A

To adapt to the various engine variants, manual or automatic transmission and different versions of the rear axle brake calipers, control modules must be coded with the Hand-Held Tester after installation in the vehicle variant concerned.

The ETS/SPS control module is divided up functionally as follows:

• Signal conditioning
• Logic section
• Safety circuit
• Additional functions
• Signal conditioning 

  The following input signals are conditioned for the logic section:

  • 4 speed sensors
  • Stop lamp switch, 4-pin
  • Terminal 61
• Logic section 

  The conditioned input signals are processed in the logic section and converted into output signals.

  The logic section is divided up functionally as follows:

  • ETS control mode
  • Starting-off control logic (manual transmission)
  • Temperature monitoring

ETS control mode 

The control mode for brake intervention on one side  is recognized from the vehicle speed and ETS slip recognition between the left and right drive wheel.

Switching on condition: Speed difference between the left and right rear wheel > 4 km/h

Switching off condition: Speed difference between the left and right rear wheel = 2 km/h below the switching-on threshold.

Speed range: 0-40 km/h

If the switching on condition is maintained above 40 km/h during an acceleration process, the control mode is continued up to max. 80 km/h.

The control mode for brake intervention on both sides  is recognized from the vehicle speed/cornering and ETS slip recognition.

Switching on condition: Both rear wheels at least 2.8 km/h faster than the vehicle speed

+

Cornering recognition:

Speed difference between the left and right front wheel > 1 km/h

+

speed range = 15-80 km/h

On period: max. 2 seconds

Starting-off control logic (manual transmission) 

A starting-off logic circuit is integrated into the ETS/SPS control module to prevent the engine "stalling" due to brake intervention when starting off.

Depending on the vehicle speed, a mean minimum rear axle speed (= theoretical minimum engine speed) is specified which depends on the current ETS brake control pressure.

If the mean rear axle speed is less than the specified mean minimum rear axle speed, pressure is reduced in the brake caliper.

This control characteristic is varied on vehicles with manual transmission depending on the brake control pressure, mean rear axle speed and vehicle speed between 4 and 28 km/h.

Temperature monitoring 

In an exceptional case, there is the risk of the rear wheel brakes overheating due to the dual load of the brake and the ETS control. For this reason the rear wheel brake lining temperature is calculated continuously in the control module and when a calculated lining temperature is reached at the respective brake, no further ETS control is permitted until the temperature has reduced again.

If ETS control is prevented by temperature monitoring, the ETS malfunction indicator lamp comes on and remains on as if the ETS control was effective, but for at least 5 seconds. The exceeded temperature is also retained in the fault memory.

Temperature calculation

The brake lining temperature is calculated separately on the left and right. It is determined without a temperature sensor.

The following inputs are evaluated to calculate brake lining temperature.

• Vehicle speed
• Brake operation
• Calculated brake pressure from the ETS control logic

After-running mode after "ignition OFF"

The voltage supply to the ETS/SPS control module is ensured by this operating mode even after "ignition OFF". As a result the brake lining temperatures continue to be calculated and cannot be reset by "ignition OFF/ignition ON". After ignition is switched off, the temperature continues to be calculated until a calculated temperature of 30°C is reached, but for a maximum of 30 minutes. The voltage supply to the ETS/SPS control module is then switched off.

Safety circuit 

The task of the safety circuit is to recognize defective components in the control module and faults in the electrical wiring system.. After "ignition ON" and when a speed of 7 km/h is exceeded for the first time, system tests are carried out, which recognize faults at the solenoid valves, the high-pressure/return pump and the speed sensors. Constant monitoring is also carried out even during ABS or ETS control. If a fault is recognized, the system is switched off and this is displayed to the driver by ETS or ABS malfunction indicator lamp (A1e35 or A1e17) coming on. A fault code is also stored in the control module.

The safety circuit also constantly monitors battery voltage. If a voltage of 10.5 V is not achieved the system is also switched off until the voltage is again in the specified range.

Additional functions 

Partial function of speed-sensitive power steering (models 140, 210) 

The control module calculates the specified current for actuating the SPS P-valve (Y10) from the vehicle speed which is available internally and the status signal.

Wheel speed and speed status signal outputs 

• Wheel speed output: The ETS/SPS control module supplies the current wheel speed of each wheel for systems which need a wheel speed signal.
• Speed status signal output: The ETS/SPS control module supplies the speed status signal for systems which need information on the current drive condition (vehicle stationary, vehicle driving, speed sensor defective).

Indicator lamp actuation 

The signals from the brake pad wear contacts and the parking brake are recorded as of control module version LK55/1. They are transmitted to the instrument cluster via a serial data bus together with the signals for the ABS and ETS malfunction indicator and warning lamps and on vehicles with CAN connection on the instrument cluster via a CAN data bus.