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

14.1.3. Equipment of measurements


Tension measurement

Existence of tension can be proved already by means of a simple control bulb or the tension indicator. However, in this case is defined only, whether tension in general moves. To define size of the enclosed tension, it is necessary to connect the voltmeter. First of all, when using the voltmeter it is necessary to establish a measurement range in which allegedly there is a measured tension. As a rule, tension in the car does not exceed 14 V.Isklyucheniye the ignition system makes: here secondary tension of system of ignition can reach till 30 000 Century. It is possible to measure this high voltage only by means of the special measuring device – an oscilloscope. First of all by means of the selector switch the range of tension of a direct current of DCV, contrary to ACV tension of an alternating current is established. Then the measurement range gets out. As the car except system of ignition has no tension above 14 Volts, it is necessary to establish the top limit of an established range of measurement slightly above (about 15-20 In). If measured tension obviously much below, for example, it is in a range of two Volts, it is possible to be switched to narrower range to reach bigger accuracy of counting. If higher tension is enclosed, than is defined by a range of measurement of the device, the last can be spoiled.

According to drawing, connect wires of the measuring device parallel to 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 mass 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 tension 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 mass of the car (–). Then charge to the assistant to press a starter and consider tension size. If tension is lower about 10 In (at temperature of the storage battery +20 ° C), it is necessary to check the storage battery and, probably, before the following attempts of start of the engine to charge it.

Current measurement

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

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

For measurement of a current it is necessary to separate an electric chain and in a rupture of a chain to connect the measuring device (ampermeter). The tip, and a red wire (+) the ampermeter is for this purpose pulled together 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 the tip should be connected by means of an auxiliary wire.


At all do not measure a current by the ordinary ampermeter in a wire going to a starter (about 150 And), or in glow plugs at diesel engines (to 60 And). 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 size of a current is measured by means of an induction.

Resistance measurement

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

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

Resistance measurement in the car is subdivided into two main areas:

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

"Test for current passing" in the 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 by both ends of the respective electric line. If resistance is equal Oh, that in this case there passes an electric current, i.e. the electric line as it should be. 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 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 emergence of noise during driving and to avoid an istiraniye of the wires, again laid wires should be strengthened by means of an insulating tape, 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 the minimum distance in 25 mm.

When drilling openings in a body it is necessary then to smooth out, отгрунтовать and to varnish edges of openings. It is necessary to remove shavings inevitably formed at drilling from a body completely.

At carrying out 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.


If wires are disconnected from plugs of the storage battery, 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 anti-blocking system, and also.

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