LV33 electrical and electronic systems (2)

LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2) LV33 electrical and electronic systems (2)

kap all phase & 6/11/03 11:38 am Page 43 Student Workbook LV33 Electrical and Electronic Systems (2) LV33/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV33 ELECTRICAL AND ELECTRONIC SYSTEMS (2) Contents Page Introduction General Fault Finding Procedures Voltage: Exercise Short circuits Before the resistance After the resistance but before the switch (earth switched circuit) After the resistance and after the switch (earth switched circuit) Exercise Progress check 6 7 Fault Finding: Battery-charging systems Battery testing Specific gravity Parasitic drain Finding the problem circuit Charging system faults 9 10 10 11 12 12 Checking the Wiring Loom 14 Checking the Alternator: Progress check 14 16 ……… Page 17 17 18 18 19 19 20 21 Starting Systems – The Circuit: Exercise Exercise Circuit testing Accessing the terminals Testing the starter motor Pull-in test Hold-in test Removing the starter motor from the vehicle No-load test Pinion return test Other checks Starter motor brushes Starter clutch Progress check 22 23 24 24 25 25 26 Fault Finding Auxiliary Systems: Exercise Exercise Exercise Exercise 27 27 28 29 30 Good Practice: Exercise 31 32 -1Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue -2Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Introduction Diagnosis is a significant part of a vehicle technician’s responsibility With the proliferation of electrical systems on a modern vehicle, an ability to diagnose electrical faults quickly and accurately has become most valued General Fault Finding Procedures To be able to fault diagnose electrical circuits accurately and quickly, an understanding of voltage is critical An understanding of voltage coupled with the correct use of a voltmeter will enable a technician to find virtually any fault Voltage A few voltage rules must be understood and remembered: • voltage is electrical pressure – it ‘pushes’ current around a circuit • voltage will drop across a resistor • volts drop will only occur if current is flowing The amount the voltage drops by across a resistor in a circuit is dictated by the comparative value of that resistor i.e its value when compared to that of any other resistors in the circuit The bigger the value of a resistor, the greater the amount of the available voltage will be used by it, when compared to the other resistors in the circuit The voltage after the last resistor in a circuit will be volts so long as current can flow If there is only one resistor in a circuit it is also the last resistor and therefore the voltage after it will be zero so long as current is flowing A voltmeter displays the difference in voltage between the positions of the red and black probes -3Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise A simple earth switched lamp circuit Consider this circuit as serviceable and in the condition pictured (switch closed or on) Mark on the voltages at all the key points Now consider an open circuit fault in connector B (poor terminal contact) Mark on the voltages at all the key points -4Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Now consider an open circuit fault in connector F (poor terminal contact) Mark on the voltages at all the key points Now consider a high resistance fault in connector D (poor terminal contact) Mark on the voltages at all the key points -5Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Now consider a high resistance fault in connector F (poor terminal contact) Mark on the voltages at all the key points Short circuits Short faults can occur in three areas on a circuit and each area will have a different effect on that circuit Before the resistance This will result in a blown fuse, popped circuit breaker or a serious fire! Because the short to ground has reduced the circuit resistance to virtually nothing, there is no limiting factor to the amount of current that the battery will produce (except the battery’s amp hour rating) This will result in a serious over-current situation in the affected circuit After the resistance but before the switch (earth switched circuit) This means that the driver cannot switch off the affected circuit The resistance has its usual permanent supply but it now has a permanent earth courtesy of the fault If the circuit is one where the consumer (lamp for example) is not normally visible to the driver – such as a luggage compartment light – the driver will complain that the battery keeps going flat This type of short circuit is known as a ‘parasitic drain’ fault as the affected circuit is draining the battery (like a parasite) -6Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue After the resistance and after the switch (earth switched circuit) This is probably the best kind of short circuit fault as it isn’t actually a fault! In fact, it can be considered something of a bonus because if the proper earth for the circuit should develop a problem (such as a resistance build up at the earthing bolt) we have our ‘fault’ to fall back on! Exercise Draw these three differing short circuit faults on the circuits below: -7Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Progress check Answer the following questions: With an earth switched circuit, if the switch is open what should the voltage be just after the resistance? With an earth switched circuit, if the switch is closed what should the voltage be after the last resistance? -8Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Fault Finding Battery - charging systems When faced with a flat battery the key to successful diagnosis is to ascertain why the battery has gone flat Seems like an obvious thing to say, but ‘why’ is an often forgotten word A general rule that is well worth applying with diagnosis of any fault (electrical or otherwise) is this: Do not only cure the fault, cure the cause of the fault If this approach is adopted, you will have very few vehicles being returned to you with the same fault that you claimed you had cured! So why has the battery gone flat? Is it because the vehicle has been parked up for four months while the owner has been abroad avoiding the cold weather? If so, the cure would be to charge the battery Simple Has the battery’s performance degenerated over time? If so, the chances are the battery has succumbed to general wear and tear and is no longer able to receive a charge successfully (plate sulphation or an overly dilute electrolyte is normally the reason) Has the battery gone flat overnight having performed brilliantly the day before? If so, the driver may have left something switched on all night, such as an interior light If not, you could be looking for a parasitic drain fault (see page 11) -9Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise Engine does not crank – automatic gearbox 12v 3v Term 50 0v 12v 3v Study the voltmeter readings on the circuit Mark onto the circuit the area where the problem lies Circuit testing The tests being performed on the circuit suggest that access must be gained to the relay terminals On a vehicle this is very difficult to because the terminals are buried in the relay block to which the relay is fitted Pulling the relay out in order to access these terminals is not the answer as you are physically breaking the circuit when you this Breaking the circuit prevents current from flowing, and volts drop will not occur Therefore the reading at the relay coil terminal would have been battery voltage (no volts drop shown across the high resistance fault in the neutral start switch) This could easily lead you to believe that there is nothing wrong with the circuit up to this point The golden rule: NEVER DISCONNECT A CIRCUIT WHEN MEASURING VOLTAGES -18Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Accessing the terminals Pull the relay out and remake the circuit using a test light The test light has been fitted across the terminals of the relay block that the coil of the relay would normally occupy The test light does not get in the way like the relay does so you can access the terminals with your voltmeter Also, the brightness of the test light when you turn the starter key to the crank position is a good indication of the condition of that side of the circuit Never be tempted to bridge these two terminals with a wire – if there is nothing wrong with that side of the circuit (i.e no high resistance or breaks) you have just created a dead short and you will blow a fuse or perhaps cause a fire Remember, your test light has resistance Testing the starter motor Once you have confirmed that the fault does not lie in the starter circuit, you can now be certain that the fault must lie in the starter motor itself A good number of workshops at this point will simply replace the starter motor as it is not economically viable to repair If your workshop does have a repair policy then you need to take your diagnosis to the next level -19Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue You can very quickly ascertain whether the fault lies in the starter motor itself or the starter circuit by bridging together terminals 50 and 30 on the starter motor If the engine cranks, then the starter motor is serviceable When doing this ensure that you make your last connection at terminal 30 - a sizeable spark is often created when carrying out this test and this can damage a small terminal such as terminal 50 to the point where you cannot refit the plug! Make sure that you use a heavy-duty bridge that has plenty of insulation – an electrical screwdriver is ideal Mainstream tool manufacturers will happily sell you a heavy-duty switch complete with crocodile clips to help you to carry out this test Pull-in test Hold-in coil supply Pull-in coil supply Terminal 30 disconnected -20Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Hold-in test The above two diagrams show a hold-in test being carried out By disconnecting the earth lead from terminal C with the pinion still out from the previous test, the pinion should remain out under the influence of the hold-in coil only If the pinion returns, then the fault lies with the hold in coil circuitry It is unlikely that the pull-in test would have been successful if the hold-in coil were faulty, as the starter motor needs both coils to engage However, it may engage with only the pull-in coil If so, the symptom is likely to be a starter that engages but then disengages instantly when on the vehicle -21Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Removing the starter motor from the vehicle The last two diagrams show a test that enables you to diagnose any problems that may lie in the pull in and hold in coil circuits within the starter motor itself It can be seen in the above diagram that the link cable between terminals C and 30 has been disconnected It can be seen from the current flow (supply) in the diagrams on the previous pages that both the pull-in and hold-in coils should now operate and the pinion should move out readily Terminal 30 has been disconnected to prevent current flowing to the field coil This is to reduce the current that is flowing through your test leads, which would otherwise be considerable You should however ensure that you use very heavy-duty cables throughout these tests If the pinion does not move out readily, the fault lies within the solenoid circuit (pull-in coil or hold-in coil) -22Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue No-load test The above diagrams show a no-load test being carried out Terminal C has been reconnected to terminal 30 and the starter motor has been connected up in a very similar fashion to the way it would be on the vehicle (minus the starter relay and the starter switch) An ammeter has been fitted in series with the battery positive lead to enable the amount of current drawn to be measured during free engagement and rotation of the starter motor This should not exceed 10 amps If it does, it is likely that the starter motor has mechanical problems such as a sticking plunger, drive lever or pinion During this test the starter motor will rotate, so excessive current could also indicate binding shaft bearings -23Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Pinion return test The pinion return test Removing the negative lead from the starter motor frame will prevent any further current flow and the pinion should move back in If it does not, the most likely fault is mechanical binding (sticking) The symptom on the car would be a starter that refuses to disengage with the ring gear when the key is released (very noisy)! Other checks The no-load test This is your opportunity to measure the voltage at terminal C with the starter ‘engaged’ The voltage should be virtually identical to that at terminal 30 If not, the starter contacts are faulty These contacts can be replaced very easily and are significantly cheaper than a starter motor -24Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Starter motor brushes If the starter motor pinion engages but the starter does not turn, the most likely fault is the commutator brushes Change these before replacing the starter motor, as they are vastly cheaper Starter clutch If the starter engages and generates a whirring noise to indicate that something is turning but the pinion does not rotate, it is likely that the starter clutch has failed -25Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Progress check Answer the following questions: What is the minimum acceptable voltage at the battery terminals during cranking? What is the minimum acceptable voltage at terminal 50 of the starter motor during cranking? If with the starter key in the crank position the voltage at terminal 30 is 12 volts and the voltage at terminal C is volts, what is the most likely fault? -26Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Fault Finding Auxiliary Systems Exercise Interior light circuit The symptom • room light works from the switch, but not off any doors • key illumination and outside handle illumination works The fault Mark on your circuit the voltage readings at key points on the circuit given to you by your tutor What is the fault? -27Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise Demister circuit The symptom • demister switch ‘on’ warning lamp works • audible ‘click’ from demister relay (!) The fault Mark on your circuit the voltage readings at key points on the circuit given to you by your tutor What is the fault? -28Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise Door locking circuit The symptom • • • doors not lock from the driver’s door key cylinder doors will unlock from the driver’s door key cylinder, doors will lock from every other key cylinder doors will lock from the drivers door master switch The fault Mark on your circuit the voltage readings at key points on the circuit given to you by your tutor What is the fault? -29Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise Door mirror circuit – left mirror ‘up’ selected The symptom • the radio works • the cigarette lighter works • left mirror will not tilt up or down • all other functions of remaining mirrors are perfect The fault Mark on your circuit the voltage readings at key points on the circuit given to you by your tutor What is the fault? -30Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Good Practice The correct way to handle electrical connectors It is sometimes very difficult to pull connectors apart – it sometimes helps to push them in hard first The correct way to remove terminals Be aware that some connectors have secondary locking mechanisms as seen in the above diagram -31Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Exercise Practical timetable Fill in the blank boxes appropriately (your tutor will tell you what faults you have to solve): 1145 1230 1330 1415 1415 1500 1500 1515 1515 1600 A B C D -32Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue ... Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue A typical IC regulated charging circuit (see Phase Electrical and Electronic Systems LV19 for details on its... serviceability of the rotor, slip rings and brushes? -16Copyright © Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Starting Systems – The Circuit Exercise... Automotive Skills Limited 2003 All Right Reserved LV33: Electrical and Electronic Systems (2) Issue Good Practice The correct way to handle electrical connectors It is sometimes very difficult