Mercedes W124

since 1985-1995 of release

Repair and car operation



W124 Mercedes
+ Governing bodies and control devices
+ MAINTENANCE
+ 2. Maintenance (diesel engines)
+ ENGINE
+ 4. Repair of 6-cylinder petrol SOHC engines
+ 5. Repair of 6-cylinder petrol DOHC engines
+ 6. Repair of the diesel engine established in the car
+ 7. Major maintenance of engines
+ COOLING SYSTEM
+ FUEL SYSTEM
+ 10. System of injection of BOSCH CIS-E fuel (KE-JETRONIC)
+ 11. System of injection of BOSCH HFM fuel
+ 12. Fuel system of diesel engines
+ 13. Fuel system of diesel engines
+ SYSTEMS OF START, IGNITION
+ 15. System of ignition of 4-cylinder petrol engines
+ 16. System of ignition of four-cylinder petrol engines
+ PRESTARTING HEATING
+ TRANSMISSION
+ 19. Mechanical transmission
+ 20. Automatic transmission
+ POWER SHAFTS
+ BRAKE SYSTEM
+ SUSPENSION BRACKET
+ BODY
- ELECTRIC EQUIPMENT
   25.2. General information
   25.3. Electric chains
   25.4. Detection of a faulty electric chain
   25.5. Safety locks and relay
   + 25.6. Switches
   + 25.7. Bulbs of external lighting
   + 25.8. Bulbs of internal lighting
   25.9. Devices of external lighting
   25.10. Adjustment of light of headlights
   25.11. Combination of devices
   25.12. Elements of a combination of devices
   25.13. Cable of a drive of a speedometer
   25.14. Lighter illumination
   25.15. Sound signal
   25.16. Screen wiper lever
   25.17. Screen wiper drive
   25.18. Screen wiper of a back door
   25.19. Elements of system of a washer of a windscreen and headlights
   + 25.20. Sound-reproducing equipment
   25.21. Loudspeakers
   25.22. System elements cruise control
   25.23. Safety cushion
   25.24. Safety cushion elements
   + 25.25. Electric circuits
+ CHECK OF MALFUNCTIONS






25.4. Detection of a faulty electric chain

GENERAL INFORMATION

The usual electric chain consists of an electric element, switches, the relay, engines, safety locks, automatic switches, wires and sockets which connect an electric element to the accumulator and a body. For the help by search of sources of malfunction of system of electric equipment look electric circuits in subsection 25.25.

Before to try to define a malfunction source, in the beginning study the corresponding scheme of electric equipment for receiving idea of the elements established in this chain. The circle of possible sources of malfunction can be narrowed if to check functioning of other elements entering into this chain. If some elements or chains выхолят out of operation at the same time, a problem, obviously, consist in a safety lock, the general for these chains or elements, or contact to a body.

Electric problems are usually caused by the simple reasons, such, as the weakened or rusted sockets, absence of contact to a body, the fused safety locks, the melted burned-through crossing point or the faulty relay. Visually check a condition of all safety locks, wires and sockets in the failed chain before to start check of other elements. Use electric equipment schemes for definition of what of trailer clips are necessary for checking for detection of a source of malfunction.

The main tools necessary for detection of a source of malfunction are the tester or the voltmeter (a bulb on 12 volts and pair of wires with щупами on the ends also can be used for carrying out some checks); ohmmeter; the battery and a set of wires with щупами, a cap puncture, it is desirable with the automatic switch or a safety lock which is used for round of checked wires or elements.

For detection of the reason of unreliable work any of elements (usually because of bad connection or pollution of contacts, or), it is possible to inspect the damaged isolation by stirring of wires. It is necessary to shake a wire by a hand to check, whether there is a malfunction at wire movement. Such method it is possible to narrow a circle of possible sources of malfunction to any wire.

Along with problems because of bad connection of the wires, two main types of malfunctions can take place in electric equipment system - the opened chain or short circuit.

Problems with the opened chain appear as a result of break in an electric equipment chain that interrupts current course. The opened chain will cause shutdown of an element of electric equipment.

Problems with short circuit are caused by short circuit of a site of a chain that leads to leakage of a current from other chain, usually directly on a body. Short circuit is usually caused by a rupture of isolation of wires that allows a wire to concern other wire or any earthed element, for example a body. Short circuit usually leads to a peregoraniye of the corresponding safety lock.

Detection of a rupture of a chain

For check of integrity of a chain, connect the device for verification of schemes or negative щуп the voltmeter to the negative plug of the accumulator or the earthed element.

Connect the second щуп to connection in a checked chain, it is desirable for the next to the accumulator or a safety lock. Thus this site of a chain should be energized from the accumulator if only the connection socket to the accumulator does not carry out a current or did not fuse a safety lock (thus do not forget that some chains of electric equipment join only at key turn in the ignition lock in a certain situation).

Include the chain, then connect щуп a tester to the connection closest to the switch of a chain on the party of the checked element.

If tension is present (about what the control bulb testifies or voltmeter indications), it means that the chain site between the corresponding connection and the switch has no gaps.

Continue chain check by the same image, and after site detection on which there is no tension, it means that the rupture of a chain occurred between this point and a point of the previous check on which there was a tension. The majority of problems of the opened chain are caused by the broken or weakened socket.

Detection of a source of short circuit

For detection of a source of short circuit, in the beginning disconnect elements of loading of a chain (elements of loading of a chain are elements which consume an electric current, such as bulbs, electric motors, heating elements etc.).

Remove the corresponding safety lock and connect щупы a tester or the voltmeter to safety lock plugs.

Include a food in chains, thus do not forget that some chains of electric equipment join only at key turn in the ignition lock in a certain situation.

If tension is present (about what the control bulb testifies or voltmeter indications), it means that in a chain there is a short circuit.

If at carrying out check of tension is not present, however the safety lock on the former fuses at connection of that loading of a chain, it testifies to failure of an element of loading.

Detection of bad grounding

The negative plug of the accumulator is connected to "weight" - to metal of a body, the engine or a transmission thus many elements of electric equipment are connected in such a manner that only the positive wire, thus a current approaches to them comes back to the accumulator through body metal. It means that fastening of an element of electric equipment and a body are a part of an electric chain. Thereof, the bad or rusted fastening can cause refusal of work of an element or lead to its unstable or bad work. In particular, bulbs can burn with dim light (especially if in a point of grounding of this bulb grounding of any else included element of electric equipment is carried out), electric motors can slowly work, and also work of one chain can have effect imperceptible at first sight on work of other chain. Do not forget that on many cars grounding wires between some elements, such as engines / transmissions and a body, that is in those places where there is no direct contact between metal elements, because of soft rubber fastenings or a paint coat are used.

For check of reliability of grounding of an element, it is necessary to disconnect the accumulator and to connect one of щупов an ohmmeter to reliably earthed element. Connect another щуп to a wire пли to connection with a body which is necessary for checking. Resistance shown by an ohmmeter should be equal to zero; if is not present, check connection as follows.

If you assume absence of grounding, disassemble connection and clear a site of a body and the wire plug (or a surface of grounding of an element) to pure metal. Carefully remove all traces of dirt, then by means of a knife remove all paint so that reliable contact of two metal surfaces turned out. At assembly, reliably tighten socket fastening; at connection of the plug of a wire, establish a washer with the jagged edges between the plug and a body surface for ensuring reliable connection. At connection, prevent emergence of corrosion in the future, having put a layer of vaseline or silicone greasing.