Mercedes C-Class

W203 since 2000 of release

Repair and car operation

Diagnostics of malfunctions of onboard electric equipment - the general information

Procedures and codes of diagnostics of systems of electronic control are considered in Head engine Electric equipment.

The structure of a typical electric contour can include an electric component, various switches, the relay, electromotors, safety locks, fusible inserts or the breakers of a contour concerning this component, and also conducting and the electric sockets serving for connection of a component with the battery and mass of a body. 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.

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

Electric equipment refusals often speak the elementary reasons, such as corrosion of plugs, safety lock failure, 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 its component.

In case of application for troubleshooting of diagnostic devices carefully plan according to 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 number of the main diagnostic devices includes a tester of electric chains or the voltmeter (it can be used also 12 In a control lamp with a set of connecting wires), the indicator of conductivity of a piece of a contour (sampler) including a bulb, own power supply and a set of connecting wires. Besides, always it is necessary to have in the car a set of wires for engine start from the auxiliary source, equipped with type clips a crocodile and, it is desirable, the breaker of a contour which can be applied to shunting and connection various an electric equipment component in the course of contour diagnostics. As it was already mentioned above before starting chain check by means of the diagnostic equipment, determine by schemes of a place of its connection.

Tension stock-taking

Stock-takings of tension are made in case of violation of functioning of a contour. Connect one of wires of a tester of electric chains or to a negative pole of the battery, or to well earthed point of a body of the car. Other wire of a tester connect to the plug of the electric socket of the contour preferably closest to the battery or 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 operate in a similar manner, investigate the contour rest. Detection of lack of tension speaks about malfunction existence between this point of a contour and the last from checked earlier (where tension was present). In most cases a cause of failure is weakening of electric connections and violation of quality of contacts.

Remember that a food on some of contours of onboard electric equipment moves only in positions of the ASS ignition key (Lay) or «RUN» (Movement).

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 should be absent. Pull conducting, watching a lamp sampler. If the lamp starts to blink, somewhere in this plait there is a short circuit on the weight, probably caused by wiping of isolation of a wire. Similar check can be made for each of a contour component, including switches.

Check of serviceability of grounding

This check is made for the purpose of determination of reliability of grounding of a component. Disconnect the battery and connect one of wires of the lamp sampler equipped with the independent power supply to the obviously well earthed point. Other wire of a lamp connect to a checked plait or the plug. If the lamp lights up, grounding as it should be (and on the contrary).

Conductivity stock-takings

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

Break localization

At diagnostics of 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 twitchings of the case of the socket on the sensor or a plait of its wires in many cases leads to conductivity restoration. Do not forget about it in attempts of localization of a cause of failure of a 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 at all does not represent a stubborn task under condition of a clear idea that the current arrives to all electric loadings (a lamp, the electromotor, etc.) from the battery on wires via switches, the relay, safety locks, fusible inserts, and then comes back to the battery through mass of the car. Any problems connected with refusal of electric equipment can have the reason only interruptions of supply on them an electric current from the battery or its return to it.