Electronic Traction Support (ETS)
NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID
General
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 Electronic Traction Support/Speed Sensitive Power Steering (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 greater than 4 km/h
Switching off condition:
Speed difference between the left and right rear wheel equals 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
Plus
Cornering recognition:
Speed difference between the left and right front wheel greater than 1 km/h
Plus
speed range equals 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 (equals 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 of30°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 (S Class (140) And E Class (210) Models)
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 Antilock Brake System (ABS) and ETS malfunction indicator and warning lamps and an vehicles with Controller Area Network (CAN) connection on the instrument cluster via a CAN data bus.
Task
To perform all Antilock Brake System (ABS) and Electronic Traction Support (ETS) brake control functions.
On vehicles with Speed-Sensitive Power Steering (SPS), (S Class (140) and E Class (210) models only) the control module also has the electronic system and control logic required for this.
To supply other systems with the vehicle speed signal, the wheel speed status signal and the stop lamp switch signal. To supply the instrument cluster with the signals for the lamps: ABS Malfunction Indicator Lamp (MIL) (A1e17), ETS MIL (A1e35) or Brake Assist System/Electronic Traction Support (BAS/ETS) malfunction indicator lamp (A1e49) and ETS warning lamp (A1e36). On the control module version LK55/1 or /2 also with the signal for the brake pad wear indicator lamp (A1e6) and low brake fluid level/parking brake indicator lamp (A1e7) via a serial line or Controller Area Network (CAN). In addition on ML model (163): Signal for brake fluid level and fault in the electronic brake booster pressure for activating the low brake fluid level/parking brake/brake booster pressure indicator lamp (A1e7) and the warning buzzer (A1h1)
Design
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There are many versions of the ASR/ETS control module. They can be identified by the housing (e.g. SK 16).
NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID
SK16 Housing
SL (129) and S Class (140) Models with module box
LK55 Housing
C Class (202) Models up to 08/95
E Class (210.004/010/020/035/O37) Models up to 05/96
E Class (210.053/055 except Japan and USA) Models
Model 210.055 (Japan and USA model year 96)
LKS511 Housing
(shortened housing on vehicles without SPS as of06/96)
C Class (202) models as of 09/95.
E Class (210.004/010/020/035/037) models as of 06/96
E Class (210.055) as of model year 97
All other E Class (210) models as of start of production
ML (163), SLK (170) and CLK (208) as of start of production
SL (129) and S Class (140) models with control module box