S-class W202 Mercedes

1993-2000 of release

Repair and car operation

W202 Mercedes
+ 1.2. General information
+ 2. Maintenance
+ 3. Engines
+ 4. Greasing system
+ 5. Cooling system
+ 6. Heating, ventilation
+ 7. Ignition system
+ 8. Fuel system
+ 9. Transmission
+ 10. Running gear
+ 11. Steering
+ 12. Brake system
+ 13. Body
- 14. Electric equipment
   14.1.2. Measuring devices
   14.1.3. Equipment of measurements
   14.1.4. Electric equipment checks
   14.1.5. Sound signal
   14.1.6. Replacements of safety locks
   + 14.1.7. Storage battery
   + 14.1.8. Generator
   + 14.1.9. Starter
   14.1.10. Traction relay
   + 14.1.11. Lighting system
   14.1.12. Devices
   14.1.13. Dashboard
   14.1.14. Filament lamps on the dashboard
   14.1.15. Light switch
   14.1.16. Radio receiver
   + 14.1.17. Aerial
   14.1.18. Loudspeakers
   + 14.1.19. Rubber brushes of screen wipers
   14.1.20. Jets of a stekloomyvatel
   14.1.21. Washing nozzles of headlights
   14.1.22. Screen wiper and its engine
   14.1.23. Protect the car
   14.1.24. Anticreeping "immunodeficiency"
   14.1.25. Why headlights grow dull
   14.1.26. "Galogenki"
+ 14.2. Electroschemes

b47c026d b47c026d

14.1.4. Electric equipment checks


At search of malfunctions in electric equipment the system approach is important. It is fair both at check of the failed filament lamps, and in case of idle electric motors.

The first step always is safety lock check as it protects an electric element of a design. The actual arrangement of safety locks can be seen on a napechatka being on a cover of the block of safety locks.

If necessary replace a faulty safety lock and after connection of the electric consumer check, whether it fused again. In this case first of all it is necessary to find malfunction and to eliminate it, here, as a rule, it is a question of short circuit.

Second control step: If at a serviceable safety lock the filament lamp is not shone, or the electric motor, respectively, does not work, it is necessary to check a power supply system.

Filament lamp check

Take and examine a lamp. If fused a filament or a glass cylinder it is weakened sits in a socle, it is necessary to replace a lamp.

To define, whether the filament lamp is serviceable, arrive as follows:

Connect directly to poles of the storage battery a positive wire (+) and earthing (on the car case) a wire (–) and connect them to a lamp. Thus it is not important, what wires are connected to a lamp. One wire attach to токопроводу, another – to the filament lamp case. If now the lamp is not shone, replace it.

It is necessary to be sure that contacts on a lamp and the lamp boss are not covered with corrosion. If necessary correlated or bent conclusions smooth out a grinding skin and make normal contact.

If the lamp is serviceable, insert it and include. If the lamp is not shone, by means of a control bulb check power supply giving. For this purpose connect a control bulb to mass of the car. I.e., one wire of a control bulb should be connected to a good point of the case on the engine (the polished metal) or is direct to a negative pole of the storage battery. Another щуп a control bulb (+) hold or on the current carrying tip, or connect it to a wire being energized. If now the control bulb lights up, and the lamp nevertheless does not burn, the line connecting the case of the car to the filament lamp is broken off. That it to check, put to the boss of a lamp the auxiliary wire connected to the case of the car. Now the filament lamp should light up.

Instruction: there are lamps which are equipped only with one feeding line which was energized, for example, lay fire, internal illumination of the car. These lamps are directly connected by means of the case with mass of a vehicle.

If in a current carrying wire to a lamp there is no tension and the control bulb is not shone, it is very probable that the switch is faulty. Check the switch on current passing.

Check of electric motors

In the car escalating comfortableness is provided with low-power electric motors. To them the window regulator, the moved panel of a roof, system of locks of doors treat with the central management or the electric aerial, for example. At need each electric motor turns on by means of one switch usually manually. In case of the electric aerial the switch automatically copes through a radio receiver.

Check resistance of the corresponding electric motor, if necessary replace it.


Before new actuating eliminate the reason of an overload of an electric window regulator and system of locks with the central management. It can be, for example, the chilled glasses and locks or the polluted fillets of lowered glass.

If the safety lock again fuses at once, it testifies to existence of short circuit.

Unequivocally to find out, whether there is a malfunction in the engine, lay two auxiliary wires in diameter about 2 mm directly from the storage battery of the car to the electric motor. Connect a positive wire to a positive pole, and, the wire connected to the case, to an earthing pole. In case of doubt distribution of poles is defined from the schematic diagram of electric equipment. If it is necessary, for this purpose it is necessary to disassemble the electric motor. All electric motors in the car запитываются onboard tension (from 12 to 14 Volts). If now the electric motor works normally, the power supply system was faulty.


Cлишком can mean electric motor slowly rotating or working with interruptions that sliding electrographite contacts are worn-out. In that case replace these contacts.

If the engine works, according to the scheme of electric equipment establish, what feeding wire brings tension to the electric motor when the switch is put in action at earlier included ignition.

By means of a control bulb check the wire which was energized in the electric motor. As in electric motors the big current proceeds, it is possible to replace a usual control bulb with the filament lamp. These lamps are equipped with peaked test needles by means of which it is possible to puncture a connecting wire. In such simple way it is possible to check tension. Engines which alternately rotate to the left / to the right, for example, engines of window regulators, have two plusovy conclusions.


Check the screen wiper engine.

If on the electric motor tension does not arrive, the power supply system is faulty; find defect in the bringing line according to the schematic diagram of electric equipment and eliminate it. As a rule, because of high consumption of a current, electric motors have the additional switching relay.

If malfunction is not found, check the switch.

If the wire is damaged, it is often more rational to lay a new wire as under isolation it is difficult to define a gap place.

Check of switches on current passing

The majority of electric consumers join and switched off by means of manually pressed switch. Besides, there are switches, with an automatic drive. Such switches treat, for example, the switch with a hydraulic actuator (the pressure drop sensor in brake system) and the sensor of level of brake liquid.

In principle, the switch has a task to close or break off an electric chain. There are switches which break off the earthing line, and switches which break off the line of a positive pole.

Check of switches of lamps and electric motors

Remove the corresponding switch.

Simple switches have only two conclusions for wire connection. In this case on one conclusion tension (+), and after inclusion / switching off – and on other conclusion should arrive. There are switches with several plugs. At these switches on the basis of the schematic diagram it is explained, tension should be applied to what plug. If necessary in advance include ignition.

Check by means of a control bulb, whether tension on the switch arrives. If the control bulb lights up, turn on the switch and check, whether tension arrives on the target plug also. If it so, is established that the switch functions.

If on the target plug there is no tension, it means that in a wire of giving of power supply there is a gap. On the basis of the schematic diagram of electric equipment check a supply of tension and, if necessary, lay a new wire.

Check of switches sensors

Switches sensors, for example, are the switch with a hydraulic actuator, sensors of level of brake and cooling liquid.

Connect a sampler (a control lamp or an ohmmeter) to a bringing and taking-away wire of the switch, for this purpose remove a wire from the switch.


Switches which are screwed in in the block of cylinders of the engine, have, as a rule, no wire connecting them to the case as the switch case on top of the block of cylinders of the engine serves as an earthing pole.

The switched-on switch the sampler should display "current passing". The best sampler is the ohmmeter: at the switched-on switch it shows zero Ohm, and at the switched off – infinity.

Most quicker approximately it is possible to check precautionary switches of level of cooling and brake liquid, delaying at the included ignition bringing wire from the switch and pressing it to well earthed place, for example, to the block of cylinders of the engine. If the alarm bulb on the dashboard works, malfunction is in the switch. The special case represents the switch with a hydraulic actuator (the power failure sensor in brake system): at an engine stop contact will close (the alarm bulb burns), the switch is disconnected only at a certain pressure of oil.

Relay check

In many electric chains the relay is established. The switching relay works as the switch. Example: if the driving beam of headlights by means of the manual switch joins, the relay receives team to switch a current to a driving beam of headlights. Certainly, it would be possible a current and directly a tax from the storage battery, by means of light switch. But at all elements with high consumption of a current (a headlight of a driving beam, a screen wiper, a fog light) in a chain it is connected the relay not to overload the switch, providing shorter ways of passing of a current, Near these combinational relays functional relays, for example, for stekloochishcheniye and stekloomyvaniye systems or the precautionary sound relay for the included external lighting are located also.

Check of the switching relay

At inclusion of a lighting element the relay is started, i.e. by means of a switching current the electromagnetic coil involves inside contact of the relay and thus closes an electric chain of "a working current". The working current via the relay arrives further to the consumer. Most simply operability of the relay can be checked, having replaced it serviceable. So arrive even in a repair truck. As the owner of the car seldom has at once on hand a new relay, in such cases it is recommended to perform the following operation in case of so-called, switching relays which are applied, including, to inclusion of fog and main lights. The marking of plugs specified here, first of all, at serially established relays, can be presented and in a different way.

Get the relay from the holder.

Include ignition and the corresponding switch.

At first establish by means of the tension indicator, whether tension on the plug 30 (+) in the holder of the relay arrives. For this purpose connect the tension indicator to the case (–), and other contact carefully enter into the plug 30. If the svetoizluchayushchy diode flashes, tension is. If the indicator of tension does not show tension, according to the basic electroscheme find break of the wire going from a positive pole of the storage battery (+) to the plug 30.

Make of a piece of the isolated wire a current-carrying crossing point, having smoothed out it to shine.

By means of this crossing point in the holder of the relay connect the plug 30 (+ the storage battery always is energized) to an exit of closing contact on the plug 87. By means of this working operation the same is practically carried out, as at installation of the serviceable relay.

If with a crossing point the driving beam, for example, lights up, it is possible to consider that the relay is faulty

If the driving beam does not light up, find out, whether as it should be connection on the case at headlights. In this case find and eliminate a gap in the line from the plug 87 to the main headlight, using the scheme of connections. If it is required, establish the new relay.


If defect in an electric chain which is equipped with one relay, is shown only periodically, in this case, as a rule, malfunction is concluded in the relay: contact in the relay or contact too залипает while in the rest of the time of the relay functions normally vanishes. At defect manifestation slightly knock on the relay case. If after that the relay is switched, replace it.

Check of the engine of a screen wiper

The engine of a screen wiper is established in a catchment basin, under a windscreen. For check it is necessary to remove the corresponding casing.

Marking of plugs

Plugs on the engine are standardly designated as follows:

 – the plug 31 is a plug for connection with the case (in general in electric equipment of vehicles);
 – the plug 53 – receives tension for the first speed of a screen wiper;
 – the plug 53а – delivers a positive current (+) for installation in a starting position of brushes of a screen wiper: the engine receives until then tension through sliding contact while screen wipers work in a starting position if the driver switches off screen wipers;
 – the plug 53в – submits tension for the second speed of a screen wiper (a parallel winding);
 – by means of the plug 53е the screen wiper engine is braked at movement back after shutdown in order that screen wipers did not leave the stopping situation;
 – the plug 53с (from the relay) – submits tension on the electric pump of a screen wiper.

Check of the engine of a screen wiper

For a start find out, whether the engine of a screen wiper and whether as it should be electroproviding system is serviceable. For clarification of it arrive as follows:

 – disconnect from the screen wiper engine the multicontact shtekkerny socket;
 – by means of two auxiliary wires submit tension (+) and weight (–) from the storage battery on the screen wiper engine;
 – one wire lay from a positive pole of the storage battery to the plug 53 or 53в;
 – the second wire carry out from a negative pole of the storage battery to the plug of 31 engines;
 – now depending on the used plug the engine should work at a step of I or II. If the engine does not work, it is faulty or its corresponding step. Remove the screen wiper engine.

Check of the device of blinking light signals

Steps for the device of blinking light signals and system of the alarm light system are developed by the relay, the so-called sensor of flashing light signals. The system of the alarm light system is connected to the relay without a safety lock. The system of the indication of turns is protected by the safety lock being in the block of safety locks.

If a rhythm of the blinking device quicker on one party, than on another, on the "fast" party the filament lamp is faulty or there is a chain break.

At emergence of other defects in most cases the reason is the breaker of indexes of turns (the sensor of flashing light signals).

On the breaker of indexes of turn the following positions of plugs are specified:

 – the plug 31 is mass of the car (a minus in electric equipment of all vehicles);
 – the plug 49 – a relay entrance (plusovy tension constantly moves);
 – the plug 49а – a relay exit;
 – the plug C conducts to a control bulb on the dashboard, in the presence of the towing device there can be an additional C2 plug for the alarm system of inclusion of indexes of turn of the trailer.

If you have no new relay, carefully insert a thin wire between plugs 49 and 49а in the relay shtekkerny socket.


Thus do not damage sensitive relay contacts. Before insertion bend the wire ends that there were no keen edges. Again get the faulty breaker of indexes of turn. Extend so connecting shinka that it was possible to get again the breaker, despite shunting.

Include ignition. If in action the lever of indexes of turn now is put, the long time is shone the relevant party of the device of blinking light signals. By means of inclusion and switching off of this device it is possible to create a blinking rhythm.

If, despite shunting, blinking fire is not shone, the switch of indexes of turn in the electric bringing line is faulty.

Check of a signal of braking

If the braking signal is not shone, first of all, check a safety lock in the block of safety locks.

If a safety lock as it should be, check filament lamps of a signal of braking, if necessary replace fused lamps.

If filament lamps are serviceable, check the switch of a signal of braking which is established from above to a brake pedal on its rack. At a nazhimaniye on a pedal of a brake press the pin is pulled out from the switch. Contact of the switch becomes isolated and the braking signal lights up.

Check the switch of a signal of braking. For this purpose remove a protective casing from above pedals. Remove a tip of wires from the switch of a signal of braking.

Switch off ignition.

Zashuntiruyte both contacts in a tip of wires of the switch of a signal of braking by a short auxiliary wire. If braking signals now light up, the switch of a signal of braking is faulty and it is necessary to replace it.

Check of a heater of back glass

At inclusion of a heating system of back glass after some time the area with visible paths should be released from a raid or ice.

At malfunctions at first check a safety lock in the block of safety locks.

If the safety lock is serviceable, check rigid landing of a tip of wires by turn it to the left and to the right on back glass, if necessary clear it of corrosion products.

If nevertheless the heating system of back glass does not function, check integrity of bringing wires and operability of the switch, and also the switching relay.

If heating lines are broken off, for restoration of their connection the current-carrying silver varnish helps. For this purpose clear the damaged zone a thinner or ethyl alcohol.

The broken-off place from both parties paste over with a sticky tape and put with a small brush a silver varnish.

Leave a varnish to dry at temperature about +25 degrees during 24 h. It is possible to warm up it hot air. At temperature 130 ° About a varnish dries approximately in 30 minutes.


Do not include a heating system of back glass while the varnish will not dry completely. To cleaning of the damaged part do not apply gasoline or other solvent.