This section describes the maintenance and repair procedures for some elements of the on-board electrical equipment system. In addition, diagnostic procedures for general electrical equipment faults are considered.
The Passat is equipped with a Controller Area Network (CAN) device. It combines individual control devices into a common circuit (data bus), which provides the following advantages: fast data transfer from one device to another, space saving due to the use of small boards and components, reduction in the number of sensors due to their multifunctionality.
How CAN works
Instead of a separate conductor for each signal, only two common wires are used, which allows you to simultaneously receive information about the status of most devices and sensors without using separate toggle switches.
CAN bus receiving important information (for example, about a malfunction), fixes it in his memory.
Safety precautions
When repairing electrical equipment and the engine power supply system, disconnect the wire from the "–" terminal of the battery.
When replacing fuses, do not use screwdrivers or metal tools, as this may cause a short circuit in the electrical circuits.
It is prohibited to disconnect the ignition switch and battery while the engine is running, as this will lead to failure of the voltage regulator and electronic components of the vehicle.
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When checking electrical equipment circuits, it is prohibited to short-circuit the wires to ground (check the circuits for a spark), as this may lead to failure of the electrical equipment components.
It is prohibited to connect the "30" terminal of the generator to the "ground" even for a short time (check the generator operation "for a spark"), as this will lead to failure of the diodes of the generator rectifier unit. The generator on the car can only be checked with a voltmeter and ammeter. To avoid failure of the diodes of the rectifier unit, it is prohibited to check them with a megohmmeter or a test lamp supplied with a voltage of more than 12 V, as well as to check the electrical circuits of 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 car, with the terminals of the stator winding disconnected from the rectifier unit.
When carrying out electric welding work on a vehicle, it is necessary to disconnect the wires from the terminals of the battery and generator.
Do not touch ignition system components or high-voltage wires while the engine is running.
Do not run low and high voltage wires in the same bundle.
When recharging the battery in a vehicle using a charger, disconnect the wires from the battery terminals.
Checking for supply voltage
Checks for the presence of supply voltage are performed in the event of a malfunction of the electrical circuit. Connect one of the leads of the electrical circuit tester to either the negative terminal of the battery or to a well-grounded point on the vehicle body. Connect the other lead of the tester to the terminal of the electrical connector of the circuit being tested, preferably the one closest to the battery or fuse. If the tester's indicator lamp lights up, supply voltage is present on that section of the circuit, which confirms the integrity of the circuit between that point in the circuit and the battery. Continuing to do so, examine the remainder of the circuit. Detection of the absence of supply voltage indicates a malfunction between that point in the circuit and the last of the previously checked points (where the supply voltage was present). In most cases, the cause of failure is the weakening of electrical connectors and poor quality of the contacts themselves (oxidation).
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