Mercedes S-Class W-140

1991-1999 of release

Repair and operation of the car

Mercedes S-Class
+ Mercedes-Benz cars of the class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Cooling systems, heating
+ Power supply system and release
+ Engine electric equipment
+ Gear shifting box
+ Automatic transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
- Onboard electric equipment
   Diagnostics of malfunctions of onboard electric equipment - the general information
   Check of the electric motor of a screen wiper
   Check of the warmed back glass
   Replacement of glow lamps
   Electric safety locks
   Installation of electric and electronic devices
   Arrangement of the basic electric elements of system of electric equipment of a body of the car
   + Schematic diagrams of electric equipment

Diagnostics of malfunctions of onboard electric equipment - the general information

Procedures and codes of diagnostics of systems of electronic control are considered in the Head Elektrooborudovaniye of the engine.

Various switches, the relay, electric motors, safety locks, fusible inserts or breakers of a contour concerning this component and also the conducting and electric sockets serving for connection of a component with the battery and mass of a body can be a part of a typical electric contour electric components. For simplification of a problem of search of malfunctions of electric contours at the end of the Management schematic diagrams of electric connections are enclosed (see. Schematic diagrams of electric equipment).

Before starting works on elimination of malfunctions any of electric contours, attentively study the corresponding scheme as much as possible to have a clear view of its functional purpose. Narrowing of a circle of troubleshooting is usually run due to gradual identification and an exception of normally functioning components of the same contour. At simultaneous failure at once of several components or contours burn-out of the corresponding safety lock or violation of grounding is the most probable cause of refusal (different contours in many cases can become isolated on one safety lock or the plug of weight).

Failures of electric equipment often are explained by the elementary reasons, such as corrosion of plugs, failure of a safety lock, combustion of a fusible insert or defect of the relay of switching. Make visual check of a condition of all safety locks, conducting and electric sockets of a contour before starting more concrete check of serviceability of its components.

In case of application for troubleshooting of diagnostic units carefully plan according to the enclosed electric circuits in what points of a contour and in what sequence it is necessary to connect the device for the purpose of the most effective detection of defect.

The tester of electric chains or the voltmeter (the 12-voltny lamp sampler with a set of connecting wires can be also used), the contour piece continuity indicator (sampler) including a bulb, own power supply and a set of connecting wires are among the main diagnostic units. Besides, it is always necessary to have in the car a set of the wires for start of the engine from an auxiliary source equipped with clips like crocodile and, it is desirable, the contour breaker which can be applied to shunting and connection of various components of electric equipment in the course of diagnostics of a contour. As it was already mentioned above before starting check of a chain by means of the diagnostic equipment, determine by schemes of the place of its connection.

Verification of tension

Verifications of tension are made in case of violation of functioning of a contour. Connect one of wires of a tester of electric chains to a negative pole of the battery, or to well grounded car body point. Other wire of a tester connect to the plug of the electric socket of a contour, preferably the next to the battery or to a safety lock. If the control lamp on a tester lights up, tension on this piece of a chain takes place that confirms serviceability of a contour between this plug and the battery. Continuing to work in a similar manner, investigate the contour rest. Detection of lack of tension speaks about existence of malfunction between this point of a contour and the last from checked earlier (where tension was present). In most cases weakening of electric connections and violation of quality of contacts is a cause of failure.

Remember that food on some of contours of onboard electric equipment moves only in provisions of the 1 or 2 ignition key (see the Section Governing bodies and the equipment of salon of the Head the Operation manual).

Searches of short circuit

One of methods of searches of short circuit is extraction of a safety lock and connection instead of it of a lamp sampler or the voltmeter. Tension in a contour has to be absent. Pull conducting, watching a lamp sampler. If the lamp begins to blink, somewhere in this plait there is a short circuit on "weight" which is perhaps caused by wiping of isolation of a wire. Similar check can be made for each of contour components, including switches.

Check of serviceability of grounding

This check is made for the purpose of definition of reliability of grounding of a component. Switch-off the battery and connect one of wires of the lamp sampler equipped with the independent power supply to obviously well grounded point. Connect other wire of a lamp to the checked plait or the plug. If the lamp lights up, grounding as it should be (and vice versa).

Conductivity verifications

Check is made for the purpose of identification of breaks of an electric chain After power off of a contour check it by means of the lamp sampler equipped with the independent battery. Connect sampler wires to both ends of a contour (or by the "power" end (+) and well grounded body point) if the control lamp lights up, the break in a contour is absent. The refusal of inclusion of a lamp demonstrates violation of conductivity of a chain. Similarly it is possible to check also serviceability of the switch, having connected a sampler to its plugs. At transfer of the switch to situation "Vkl" the lamp sampler has to light up.

Break localization

At diagnostics of the break of a contour suspected on existence visually to find a cause of defect it appears quite difficult as survey of plugs on existence of corrosion or violation of quality of their contacts is complicated in a type of limitation of access to them (usually plugs are closed by the socket case). Sharp or a plait of its wires in many cases leads twitchings of the case of the socket on the sensor to conductivity restoration. Do not forget about it in attempts of localization of a cause of failure of the contour suspected on break. Unstably arising refusals can have the reason oxidation of plugs or violation of quality of contacts.

Diagnostics of malfunctions of electric chains does not represent a stubborn task on condition of a clear idea that current arrives to all electric loadings (a lamp, an electric motor, etc.) from the battery on wires via switches, the relay, safety locks, fusible inserts at all, and then comes back to the battery through "mass" of the car. Any problems connected with failure of electric equipment can have the reason only interruptions in supply on them electric current from the battery or its return to it.