7.1. General information
The Audi cars have system of electric equipment with working voltage of 12 V. Electric equipment is executed according to the single-wire scheme – negative conclusions of sources and consumers of the electric power are connected to a body of the car which performs function of the second wire. Power supply of all lighting fixtures and electric units is carried out from the battery of lead-acid type recharged from the generator of alternating current.
The present section is devoted to the description of procedures of service and repair of some elements of system of onboard electric equipment. Besides, procedures of diagnostics of malfunctions of electric equipment of the general order are considered.
On Audi the Controller Area Network (CAN) device is installed. It unites separate monitors in the general scheme (the tire of data) that gives the following advantages: bystry data transmission from one device to another, economy of the place due to application of small payments and details, reduction of number of sensors due to their multifunctionality.
Principle of work of CAN
Instead of the separate conductor for each signal only two general wires are used that allows to obtain at the same time information on a condition of the majority of devices and sensors, without using at the same time separate toggle-switches and switches.
Sheena CAN, obtaining important information (for example, about malfunction), fixes it in the memory.
At repair of electric equipment and a power supply system of the engine disconnect a wire from the - plug of the rechargeable battery.
When replacing safety locks it is forbidden to use screw-drivers and the metal tool as it can lead to short circuit in electric equipment chains.
It is forbidden to disconnect the switchboard of ignition and the rechargeable battery on the working engine as it will lead to failure of the regulator of tension and elements of the electronic equipment of the car.
When checking chains of electric equipment it is forbidden to close on "mass" of a wire (to check serviceability of chains "for a spark") as it can lead to failure of elements of electric equipment.
"30" generators are forbidden even to connect a conclusion to "weight" (to check operation of the generator "on a spark") as it will lead to failure of diodes of the vypryamitelny block of the generator quickly. It is possible to check the generator on the car only the voltmeter and the ampermeter. In order to avoid failure of diodes of the vypryamitelny block it is forbidden to check them the megohm meter or the control lamp fed more than 12 V and also to check such devices of a chain of electric equipment on the car without detachment of wires from the generator. It is necessary to check resistance of isolation of a winding of the stator of the generator the increased tension on the generator removed from the car at the stator winding conclusions disconnected from the vypryamitelny block.
When carrying out electrowelding works on the car it is necessary to disconnect wires from plugs of the rechargeable battery and the generator.
Do not concern elements of system of ignition and high-voltage wires on the working engine.
Do not lay a wire of low and high voltage in one plait.
At recharge of the rechargeable battery on the car by means of the charger disconnect wires from battery plugs.
Verification of supply voltage
Verifications of supply voltage are made in case of violation of functioning of an electric chain. Connect one of wires of a tester of electric chains or to a negative pole of the rechargeable battery, or to well grounded car body point. Other wire of a tester connect to the plug of the electric socket of the checked chain, preferably the next to the rechargeable battery or to a safety lock. If the control lamp of a tester lights up, supply voltage is present at this piece of a chain that confirms serviceability of a chain between this point of a chain and the rechargeable battery. Continuing to work similarly, investigate the chain rest. Detection of lack of supply voltage speaks about existence of malfunction between this point of a chain and the last from checked earlier (where supply voltage was present). In most cases, weakening of electric sockets and violation of quality of contacts is a cause of failure (oxidation).
Searches of the place of short circuit
One of methods of search of short circuit is extraction of a safety lock and connection instead of it of a lamp sampler or the voltmeter. Tension in a chain has to be absent. Pull conducting, watching a lamp sampler. If the lamp begins to blink, somewhere in this plait of wires there is a short circuit on weight which is perhaps caused by wiping of isolation of wires. Similar check can be made for each of components of an electric chain by turning on of the corresponding switches.
Check of serviceability of grounding
This check is made for the purpose of definition of reliability of grounding of an element of a chain. Switch-off the rechargeable battery and connect one of wires of the lamp sampler having the independent power supply to obviously well grounded point. Connect other wire of a lamp to the checked plait of conducting or the plug of the electric socket. If the lamp lights up, grounding as it should be (and vice versa).
Checks on lack of break
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 power supply. Connect sampler wires to both ends of a chain if the control lamp lights up, the break in a chain is absent. If the lamp does not light up, then it demonstrates existence in a break chain. Similarly it is possible check also serviceability of the switch, having connected a sampler to its plugs. At transfer of the switch to situation "Vkl" the lamp of a sampler has to light up.
Localization of the place of break
At diagnostics of the suspect on existence of break of the site of an electric chain 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 case of the electric socket). Sharp or a plait of its wires in many cases leads twitchings of the case of the socket on the sensor to contact restoration. Do not forget about it in attempts of localization of a cause of failure of the suspect on existence of break of a chain. 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 of the fact that electric current arrives to all consumers (a lamp, an electric motor, etc.) from the rechargeable battery on wires via switches, the relay, safety locks, fusible inserts, and then comes back to the battery through the mass of a body 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.
Wires, safety locks and relay
Protection of electric chains of the car against short circuit is provided with use of set of safety locks, breakers of chains and fusible inserts. It is easy to distinguish the burned-down safety lock from its transparent plastic case, serviceable by survey. Attentively examine a safety lock for identification of its burn-out. If the safety lock externally looks normally, but suspicions on its malfunction remained, make check of conductivity between the knife plugs acting from its case.
When replacing safety locks you watch compliance of face value of a new safety lock to the face value of old. The safety locks calculated on various current can look externally equally therefore special attention should be paid to marking. Replacement of the burned-down safety lock on calculated on smaller – and especially big – current is undesirable. Each electric chain needs different degree of protection. You watch that marking on the case of a safety lock corresponded to the current on which the corresponding chain is calculated. If the replaced safety lock immediately fuses, it will not be reasonable to continue its replacement. First of all, it is necessary to establish and remove the cause of its burn-out. In most cases that appears the short circuit in an electric chain caused by break or damage of isolation of a wire.
Protection of some electric chains is carried out by inclusion in them of fusible inserts. Inserts are usually used for protection of the chains which are not equipped with safety locks such as chain of system of ignition.
Fusible inserts are similar to safety locks in the sense that an exit them out of operation (oplavleniye) easily is defined visually.
For replacement of a fusible insert disconnect a negative wire from the rechargeable battery. Take the burned-down insert and establish new on its place. Before replacement of an insert surely try to define the reason of the overload which caused an insert exit out of operation.
Chain breakers (thermal relays)
Thermal relays serve for protection of such components as electric drives of window regulators, locks of doors and adjustment of provision of headlights (electroproofreaders). Some of breakers of chains are installed in the assembly block. Return of thermal relays to an initial state on some models is carried out automatically, i.e. at emergence of an overload in a chain the thermal relay is instantly disconnected, then, after cooling, reverts to the original state. If return of a contour into position does not happen, it is necessary to make its check immediately. Normal functioning of the thermal relay confirms serviceability of a contour. Some of breakers are equipped with buttons for manual compulsory return to an initial state.