This section is devoted to the description of maintenance and repair procedures for some elements of the on-board electrical system. In addition, the procedures for diagnosing malfunctions of electrical equipment of a general order are considered.
A Controller Area Network device is installed on the Passat (CAN). It combines individual control devices into a common circuit (data bus), which gives the following advantages: fast data transfer from one device to another, saving space due to the use of small boards and parts, reducing the number of sensors due to their multifunctionality.
How CAN works
Instead of a separate conductor, only two common wires are used for each signal, which allows you to simultaneously receive information about the status of most devices and sensors without using separate toggle switches and switches.
CAN bus receiving important information (for example, about a malfunction), fixes it in its memory.
Safety
When repairing electrical equipment and the engine power system, disconnect the wire from the terminal «–» battery.
When replacing fuses, it is forbidden to use screwdrivers and metal tools, as this can lead to a short circuit in the circuits of electrical equipment.
It is forbidden to disconnect the ignition switch and the battery while the engine is running, as this will lead to failure of the voltage regulator and elements of the vehicle's electronic equipment.
When checking the circuits of electrical equipment, it is forbidden to short to «mass» wires (check the continuity of the circuits «for a spark»), as this can lead to failure of electrical components.
Do not even briefly connect the output «30» generator with «weight» (check the generator «for a spark»), as this will lead to failure of the generator rectifier unit diodes. You can only check the alternator on a car with a voltmeter and an ammeter. In order to avoid failure of the diodes of the rectifier unit, it is forbidden to check them with a megohmmeter or a test lamp supplied with a voltage of more than 12 V, and also to check the electrical equipment circuits on the car with such devices without disconnecting the wires from the generator. It is necessary to check the insulation resistance of the generator stator winding with increased voltage on the generator removed from the vehicle, with the stator winding terminals disconnected from the rectifier unit.
When carrying out electric welding work on a car, it is necessary to disconnect the wires from the battery terminals and the generator.
Do not touch the elements of the ignition system and high-voltage wires while the engine is running.
Do not run low voltage and high voltage wires in the same bundle.
When recharging the battery in a car using a charger, disconnect the wires from the battery terminals.
Checking the presence of supply voltage
Checks for the presence of supply voltage are made in the event of a malfunction of the electrical circuit. Connect one of the circuit tester leads to either the negative battery terminal or a well grounded point on the vehicle body. Connect the other tester lead to the electrical connector terminal of the circuit under test, preferably the one closest to the battery or fuse. If the tester's control lamp lights up, the supply voltage is present on this section of the circuit, which confirms the health of the circuit between this point in the circuit and the battery. Continuing in the same way, explore the rest of the chain. Detection of the absence of supply voltage indicates the presence of a malfunction between this point in the circuit and the last one previously checked (where the supply voltage was present). In most cases, the cause of the failure is the loosening of the electrical connectors and the deterioration of the quality of the contacts themselves (oxidation).
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