Mercedes S-class W202

1993-2000 of release

Repair and car operation

Mercedes W202
+ 1.2. The general data
+ 2. Maintenance service
+ 3. Engines
+ 4. Greasing system
+ 5. Cooling system
+ 6. Heating, ventilation
+ 7. Ignition system
+ 8. Fuel system
+ 9. Transmission
+ 10. A running gear
+ 11. A steering
+ 12. Brake system
+ 13. A body
- 14. An electric equipment
   14.1.2. Measuring devices
   14.1.3. Technics of measurements
   14.1.4. Electric equipment checks
   14.1.5. A sound signal
   14.1.6. Replacements of safety locks
   + 14.1.7. The storage battery
   + 14.1.8. The generator
   + 14.1.9. A starter
   14.1.10. The traction relay
   + 14.1.11. Illumination system
   14.1.12. Devices
   14.1.13. The instrument panel
   14.1.14. Lamps накаливания on the panel of devices
   14.1.15. Light switch
   14.1.16. A radio receiver
   + 14.1.17. The aerial
   14.1.18. Dynamics
   + 14.1.19. Rubber brushes of screen wipers
   14.1.20. Jets стеклоомывателя
   14.1.21. Washing atomizers of headlights
   14.1.22. A 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. "Галогенки"
+ 14.2. Electroschemes

14.1.3. Technics of measurements

Pressure measurement

Pressure presence can be proved already by means of a simple control bulb or the pressure indicator. However, in this case it is defined only, whether pressure in general moves. To define size of the enclosed pressure, it is necessary to connect the voltmeter. First of all, at voltmeter use it is necessary to establish a measurement range in which presumably there is a measured pressure. As a rule, pressure in the car does not exceed 14 V.Iskljuchenie the ignition system makes: here secondary pressure of system of ignition to reach to 30 000 V.Eto a high voltage it can is possible to measure only by means of the special measuring device – an oscilloscope. First of all by means of the selector switch the range of pressure of direct current DCV, contrary to ACV-pressure of an alternating current is established. Then the measurement range gets out. As the car except ignition system does not have pressure above 14 Volt, it is necessary to establish the top limit of an established range of measurement a little above (approximately 15–20). If measured pressure is obviously considerable more low, for example, it is in a range of two Volt, it is possible to be switched to narrower range to reach большей accuracy of readout. If higher pressure are enclosed, than is defined by a range of measurement of the device last can be spoilt.

According to drawing, connect wires of the measuring device in parallel the consumer. Thus the red measuring wire is connected to a wire going from a positive pole of the storage battery, and a black measuring wire – to a wire connecting the storage battery and the case of the car, or is direct to weight of the car, for example, to the block of cylinders of the engine.

Control example: if the engine is not started properly because the starter too slowly rotates, it is expedient to check up pressure of the storage battery during starter pressing. For this purpose a red wire (+) the voltmeter attach to the red plug of a positive pole of the storage battery, and a black wire – to weight of the car (–). Then charge to the assistant to press a starter and consider pressure size. If pressure more low approximately 10 In (at temperature of the storage battery +20 ) it is necessary to check up the storage battery and, probably, before following attempts of start of the engine to charge it.

Current strength measurement

In the car rather seldom it is required to check a current strength. The ampermeter which also is built in in the combined measuring device for this purpose is required.

Before current strength measurement the measuring device is established on a range in which approximately there is a measured current strength. If it is not known, establish the highest measuring range and if there is no indication, consistently switch the device to lower ranges.

For current strength measurement it is necessary to separate an electric chain and in chain rupture to connect the measuring device (ampermeter). It is for this purpose pulled together штеккер, and the red wire (+) the ampermeter is connected to a current-carrying wire. The black wire (–) is connected to contact to which the broken off line is connected. In this case earthing contacts of the consumer and штеккера should be connected by means of an auxiliary wire.

The prevention

At all do not measure a current strength by the usual ampermeter in a wire going to a starter (nearby 150), or in candles накаливания at diesel engines (to 60). Because of high currents arising thus it is possible to burn the measuring device. In repair trucks for such measurements the ampermeter equipped with pincers of a direct current is used. Thus current-measuring pincers are clamped over the isolated electricity cable, and the current size is measured by means of an induction.

Resistance measurement

Before resistance measurement it is necessary to be assured that the design element to which the ohmmeter is connected, is not energised. Therefore each time in advance pull down штеккер, switch off ignition, a wire, for example, disconnect from the unit or disconnect the storage battery. The measuring device otherwise can be damaged.

The ohmmeter is connected to two plugs of the consumer (loading) or by two ends of an electric line. Thus does not play any role, what wire of the measuring device joins plugs.

Resistance measurement in the car is subdivided on two basic areas:

Check of the resistor built in in an electric chain or a design element.

"Test for current passage" in an electric line, in the switch or a heating spiral of a heater. It is thus checked, whether the electric chain in the car is broken off and consequently the connected electric device cannot function. For measurement the ohmmeter is connected to both ends of a corresponding electric line. If resistance is equal About in this case takes place an electric current, i.e. The electric line is perfectly in order. In case of the broken off line the measuring device shows infinity (in Ohms).

Installation of additional electric accessories


Wires which at installation of accessories should be laid to the built in complete set of wires in the car, whenever possible, should be stacked always along separate plaits with use of collars for their fastening and rubber plugs. To prevent occurrence of noise during driving and to avoid истирания the wires, again laid wires should be strengthened with the help изоляционной tapes, plastic weight, tape collars for their fastening, etc. Thus especially it is necessary to pay attention to that between pipelines of a brake drive and rigidly laid wires the minimum distance in 10 mm was maintained, and also between pipeline of a brake drive and wires which vibrate together with the engine and other details of the car, there was a minimum distance in 25 mm.

At drilling of apertures in a body it is necessary then to smooth out, отгрунтовать and to varnish edges of apertures. Shavings inevitably formed at drilling should be removed from a body completely.

At carrying out of all installation works, which concern electric conducting to prevent short circuits in system, it is necessary to disconnect a wire of weight of the storage battery (–), a pole connecting it with the car case, and to hang it aside.

The prevention

If wires under known conditions other electric devices as, for example, a radio receiver and hours, and the saved up sizes are erased are taken out of service the device of storing of malfunctions in a control system of the engine and a transmission and in antiblocking system, and also are disconnected from plugs of the storage battery.

If additional electric consumers in each case it is necessary to check up are established, whether it is possible to load available three-phase generator of an alternating current in addition still. If it is required, it is necessary to provide installation of the new generator having rather big capacity.