17.2. Search of malfunctions of electric systems - the general information
Before getting to work read the prevention, provided in the Section the General information) the checks Given below belong only to the main electric contours and should not be applied to check of difficult electronic contours, such as a contour of anti-blocking system of brakes (ABS), in particular at malfunction of electronic actuation devices (ECU).
The generalThe typical electric contour consists of electric components, switches, the relay, motors, safety locks, safety links or the thermorelay breakers of a chain depending on a component, and also wires and electric sockets connecting chain components to the battery and the case.
Before starting search of malfunctions of an electric chain at first study the corresponding electric circuit for a better understanding about structure of the elements included in this chain. The list of the possible reasons of malfunctions can be narrowed by definition of the components of this contour continuing to function normally. In case of simultaneous failure of several elements of one contour, it is the most probable that the problem consists in malfunction of contacts of a safety lock or grounding.
Often the problems arising decide on electric systems by the simplest reasons, such as the weakened or rusted electric contacts, faulty ground contacts, the fused safety locks or the melted safety links, or faulty relays (information on check of the relay is provided in the Section Safety locks and the relay - the general information). Before starting check of components of a faulty contour visually examine a condition of all safety locks, wires and electric sockets. For simplification of a task, for the purpose of definition what plugs have to be checked, study the electric circuit.
Search of electric malfunctions, requires use of the following main tools: a tester of a chain or the voltmeter (for some checks the bulb with a set of wires), a test bulb with individual food (known also under the name of the indicator of conductivity of a chain), an ohmmeter (for measurement of resistance can be used 12B), the battery and a set of wires, a set of thick wires for start of the engine from an auxiliary source, it is preferable with the safety lock attached to them - these wires are intended for contour of the suspected sites of a chain. Before starting attempt of definition of a cause of defect by means of diagnostic units, attentively study the electric circuit for the purpose of definition of points of connection of devices.
By search of the reason of unstable conductivity of wires (usually owing to the bad or polluted contact or damage of isolation of a wire) check of integrity of wires can be made by their stir manually. At the same time the list of the suspected wires can be considerable is narrowed. Such method of check can be used together with other checks described in the following subsections.
Except the problems resulting from bad electric contacts, other main reasons for malfunction of electric chains the rupture of a contour or short circuit are.
The rupture of a contour usually is caused by the break somewhere in a chain causing the termination of passing of electric current. The break of a contour causes termination of work of components, without being, however, the reason of burn-out of the corresponding safety lock.
Short circuit is caused by short circuit of open sites of a contour among themselves or with a weight, causing passing of electric current on an alternative way usually on weight. Short circuit most often is caused by violation of isolation of wires and contact of the bared sites with other wires or the grounded car components, such as body elements. Short circuit usually causes burn-out of the corresponding safety lock.
If short circuit happened in a wire to a safety lock, the safety lock does not fuse. This part of a contour is unprotected - it is worth to remember about it by search of malfunctions in electric systems of the car.
Search of breaks of a chainFor verification of break of a chain, connect a wire of a tester of a continuity of a chain or the voltmeter or to the negative plug of the battery, or to well grounded car point.
Connect other wire to contact in the checked chain, it is preferable as it is possible closer to the battery or a safety lock.
Include a contour, remembering that some contours are powered only at a certain position of the ignition key.
If tension is present (that is visible according to indications of the voltmeter or on fire of a test bulb), then it means that this site of a chain between the corresponding contact and the battery is not broken.
Similarly continue check of other sites of a chain.
After detection of a point in which tension is absent it is possible to tell with confidence that the rupture of a chain lies between this point and the last the next to it on a chain a point at which there was tension. Usually the fiasco, corrosion or weakening of fastening of contacts are the main reasons for ruptures of contours.
Search of short circuitsFor verification of short circuit first of all disconnect loading (loadings from a contour) (loadings components which consume the power given to a contour, such as bulbs, motors, heating elements, etc. are).
Take out the corresponding safety lock from a contour and connect the voltmeter or a tester of a contour to its contacts.
Include a contour, remembering that some chains are powered only at a certain position of the ignition key.
If tension is present (the voltmeter shows nonzero value or the test bulb lights up), then it means that in a contour there is a short circuit.
If tension is absent, however the safety lock continues to fuse at connection of loading (loadings), then it indicates existence of internal malfunction of load elements (element).
Grounding troubleshootingThe negative pole of the battery is directly connected to the earth - the metal case of engine / transmission or a body of the car - and the most part of systems is connected in such a way that they are connected to the battery only on a positive pole, and current comes back to the battery on car design metal. It means that support of components and a body form a part of an electric contour. Thus, weakening of fastening or corrosion of support can be the reason of electric malfunctions, beginning from full malfunction of a contour and finishing its uncertain work. In particular lamps (in particular if any other contour having the same point of grounding), motors (for example, motors of screen wipers or the electric motor of the fan of the cooling system is involved) can dimly burn can work in a slowed-up way and involvement of one contour can exert impact on work of another, the contour which does not have relations to it. Pay attention that on many cars, between separate components, grounding tires are installed, usually it is components between which there is no metal contact in a consequence of installation of flexible rubber support, for example, the block of engine/transmission and a body.
To check whether any component is reliably grounded, disconnect the battery and connect one of ohmmeter wires to unambiguously well grounded point. Connect other wire to a point of grounding of the checked component. The indication of an ohmmeter has to be zero; if it not so, check contact as follows.
If there is a suspicion on a bad ground contact, investigate contact and smooth out to naked metal the surface of the plug and a surface of a body on which it is established, or the interfaced component ground contact surface. Carefully remove all traces of dirt and corrosion, then by means of a knife scratch out paint if that is available so that the pure contact surface metal to metal was formed. At assembly hardly tighten contact fixture. At installation to the place of plugs of wires, for ensuring pure reliable contact, establish between the plug and a body (case) of a washer. After contact assembly, in order to avoid further education of corrosion, grease contact with acid-free vaseline or lubricant on a silicone basis, alternatively, through regular intervals, spray contact connection by patent sealant for systems of ignition, such as Holts Damp Start or the lubricant absorbing moisture, such as Holts Wet Start.