Combination switch
The direction indicators, wiper and light signal are controlled by a single steering column switch on the left side of the steering wheel. There is also a light control body: a combined switch for parking, dipped and fog light, rear fog lights, headlight range control.
This switch (designation «S4» on wiring diagrams) - a truly complex mechanism, since at least 12 wires are connected to it and switched in various ways. Such a combination switch was also installed on previous Mercedes models. Over the years of operation, the following problem has appeared: as it wears out, the direction indicator switch ceases to be fixed. In this case, the combination switch had to be replaced. Attempts to refine the fixation system often brought only temporary improvement.
Combination of instruments and switches
Pic. 10.7. center console
All important control switches are located on the center console (pic. 10.7). For convenience, the switches are divided into functional groups:
- in the top row there are switches for the drive of the rear head restraints, central locking and alarm;
- in the middle there is a control unit for the heating system, air conditioning and a recirculation button;
- in the lower part The center console contains the switch box for operating the power windows, the child lock and the door mirror adjustment buttons.
Looking up, you can see a new control unit for interior lighting and a sliding sunroof. There is also a ventilated sensor for the heating and air conditioning system.
Electronic engine start system
The switch of this system is practically the most important in the car and is also a new development. Electronic ignition switch - the main essence is clear from the name. The ignition lock and ignition key in the traditional sense are no longer in the Mercedes E-Class. They were replaced by a complex electronic system in which a conventional mechanical key was replaced by a device with several functions. The main difference between the electronic key is the absence of a metal beard: to start the engine, a wedge-shaped tongue is inserted into the ignition switch socket and turned to the right. Everything else is done by electronics. On models with an automatic transmission, it itself carries out the starting procedure before starting the engine.
However, first, a split-second control process takes place inside the ignition switch, during which the electronics automatically checks whether the correct key is inserted in the lock. To do this, the switch inductively supplies power to the key, which in response transmits a coded signal with infrared radiation. The ignition switch microprocessor checks the code against the stored value and, if matched, releases the electrical steering wheel lock. The key can now be turned to the right to turn on the ignition. The codes of the electronic key and the value stored in the processor's memory are changed with each new start and re-stored in the memory.
It is more convenient to check the ignition switch from the side of the connector under the steering column. By the symbols on the switch, you can understand which contacts are connected with the corresponding key position. If a problem occurs, have the ignition switch replaced at a workshop, as a special tool is required to remove it and remove the steering column.
Security system (admission system)
Since December 1994, Mercedes-Benz has been equipping all models as standard with an electronically controlled security system that meets the stricter requirements of the law and auto insurers. The main element of the new security system is an infrared remote control, designed in the form of an electronic door key. To start the engine, the vehicle door must first be opened with this remote key. Otherwise, the engine management system will remain blocked and the engine cannot be started.
A small transmitter in the key emits an invisible infrared signal combined with a radio signal to several receivers located inside the doors and behind the interior rearview mirror. The received and processed signal is transmitted to the control unit in the engine compartment. There, the signal is fixed in memory, a new code is generated, which will be needed for the next (or later) opening doors and starting the engine. At the same time, data is exchanged with the engine control unit for start inhibition and the central door locking system.
Alarm switch
The alarm switch button, when the lighting is on, is faintly illuminated by a small lamp. This is because the lamp receives voltage through the resistor. When the button is pressed, the resistor is disconnected from the circuit, and the lamp begins to shine at full power in a flashing mode.
Checking switches
If during troubleshooting in electrical equipment, it is necessary to check the switch, first find it on the diagram, and then check its connection. To do this, you can use either a probe lamp and check for voltage, or an ohmmeter in the removed state. In most cases, the first method is preferable. Check if it is possible to get the tested wire in the connector with the needle of the probe lamp. If not, the stinger can pierce the insulation. The DIP switches can only be removed after the trim has been removed. Other switches are screwed on. Many switches in a car are internally illuminated. Unfortunately, the lamps in them cannot be replaced, with the exception of the light switch.
Sequence of work
1. The needle of the probe lamp can pierce the wire insulation to check for voltage on them.
2. Have the appropriate wiring diagram handy.
3. First check if there is any voltage to the switch at all. To do this, turn on the ignition or lighting.
4. Then check if the switch transmits voltage in the appropriate position.
5. Using the ignition switch and starter as an example, the test should be carried out as follows:
- the current-carrying red wire from the positive terminal of the battery must always be energized;
- on the terminal wire «15x» ignition switch must be energized when the switch is in the positions «I», «II» and inclusion of a starter;
- on the terminal wire «15» ignition switch must be energized when the switch is in the positions «II» and inclusion of a starter;
- on the purple contact wire «50» current should flow only when the switch is in the starter on position.