10.5.1. Survey of connections
When checking the module of management of the Motronic 4.3 system do not remove it from the car until the main relay does not disconnect power supply. It occurs during 150 from later switching off of ignition.
Fig. 10.4. Check of the plug of the socket
When performing all measurements and checks which are followed by separation of sockets it is necessary to examine surely conclusions in the socket (fig. 10.4)
Check each plug and a nest for oxidation existence, both the most connecting part, and seal of a wire. Oxidation is inadmissible. Make sure that contact plugs and nests are not damaged and reliably fixed in the socket, and conductors are reliably connected to plugs/nests. Pay special attention to the plugs and nests relating to a chain in which malfunction is registered. Check reliability of fastening individually of each plug and a nest in socket cases. At easy twitching they have to remain on the place.
Break in a chain
In a chain points not passing of an electric signal from the device sending to the device accepting it or distortion of output parameters of a signal to break. Usually the worn-out, disconnected or oxidized conducting is the reason of malfunctions. Most often it happens in sockets and seals of wires. For check of the wires which are a part of the checked electrochain disconnect sockets since both ends of a wire.
Fig. 10.5. Check of break in a chain by means of an ohmmeter
Connect an ohmmeter to both ends of a wire (fig. 10.5)
and measure its resistance in the absence of break of a wire the ohmmeter has to show 0 Ohms. Be surely convinced of absence on the module of management and in the socket of a box of modules of management of the bent, or damaged plugs, or nests as this defect can become a cause of defect. Especially carefully examine the plugs and nests relating to a chain in which malfunction is registered.
Further some malfunctions which you can face when checking are given:
Short circuit between a current carrying wire and "weight" usually leads to burn-out of a safety lock of this chain, or to violation of any function (or functions).
Procedure for test:
1) turn on all switches and involve all sensors of a chain for check whether the safety lock will fuse;
2) disconnect sockets of components of a chain that they did not exert impact on results of measurements;
3) by means of an ohmmeter measure resistance between a wire and "weight";
4) at absence in a chain of components the device has to show "infinite" resistance;
5) especially carefully examine the plugs and nests relating to a chain in which malfunction is registered.
on a current-carrying wire
Short circuit of a wire on other current-carrying wire usually causes either burn-out of a safety lock, or unplanned operation of any system.
Procedure for test:
Fig. 10.6. The scheme of detection of short circuit on a current-carrying wire
1) by means of the voltmeter measure tension in various points of a chain (fig. 10.6)
, turning on at the same time switches and involving sensors. Tension shown by the voltmeter depends on a chain where measurement, and also position of switches and a condition of sensors is performed. Value of tension, normal for this chain, is given in the electric circuit;
2) if short circuit between wires is supposed, measure resistance between them by means of an ohmmeter. The ohmmeter has to show "infinite" resistance between the wires which are not connected with each other in a chain;
3) especially carefully examine the plugs and nests relating to a chain in which malfunction is registered;
The raised contact
resistance because of oxidation
Theoretically resistance of sockets, conducting and conclusions has to be equal 0 Ohms. However some resistance is always present in connection with wear and oxidation of conclusions. If this resistance becomes excessively big, functioning of systems is broken. The size of contact resistance at which functioning of system is broken depends on loading in a chain. Usually this size makes several Ohm.