Advanced Electrical Theory

TechniciansReference

Booklet

Advanced ElectricalTheory & Diagnosis

Module 602

© Copyright 2001Subaru of America, Inc.

All rights reserved. This book may not be reproducedin whole or in part without the express permission ofSubaru of America, Inc.

Subaru of America, Inc. reserves the right at any timeto make changes or modifications to systems,procedures, descriptions, and illustrations containedin this book without necessarily updating thisdocument. Information contained herein is consideredcurrent as of June 2001.

© Subaru of America, Inc. 2001 TT05046/01

Advanced Electrical Theory & Diagnosis Module

3June 2001

Table of ContentsSlide Sequence ................................................................................................4Slide Sequence ................................................................................................5

Introduction ............................................................................................................6Solid State Devices ...............................................................................................6

Testing Transistors ........................................................................................ 12Alternators .......................................................................................................... 13

Solid State Voltage Regulator ....................................................................... 14Alternator Testing Precautions...................................................................... 14

Starters ............................................................................................................... 15Starter Types ................................................................................................. 15

Operation ............................................................................................................ 15Starter/Solenoid Testing Procedures............................................................ 16

Opcilloscope Testeing and Diagnosis............................................................... 17Computer Terminology and Operation .............................................................. 18

Computer Hardware ...................................................................................... 18Computer Software ........................................................................................ 18Terminology ................................................................................................... 18

Troubleshootingn Diagnosis of Intermittent Faults ........................................... 19Intermittent Faults ............................................................................................... 20

Thermal and Mechanical ............................................................................... 20Select Monitor Usage......................................................................................... 20Electrical Symbols .............................................................................................. 22Electrical Terms Glossary .................................................................................. 23

Alternating Current (AC) ................................................................................ 23Direct Current (DC) ........................................................................................ 23Sine Wave...................................................................................................... 23Square Wave ................................................................................................. 23Resistance ..................................................................................................... 23Dynamic Resistance ..................................................................................... 23Voltage Drop .................................................................................................. 23Resistor .......................................................................................................... 23


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1 Title Slide (Advanced Electrical)2 Created By3 Teaching Aids4 Introduction 65 Title Slide (Solid State Devices) 66 Semi-Conductor 77 Lattice Structure 78 Electron Current Flow 79 Diagram of Diode 810 Diode Symbols 811 Testing Diode 912 AC Sine Wave 1013 Three Phase Sine Wave 1014 LED/PSD 1015 Zener Diode Operation 1116 PNP Transistor Construction 1117 NPN Transistor Construction 1118 Title Slide (Testing Transistors) 1219 PNP Transistor Testing 1920 Title Slide ( Alternators) 1321 Alternator Components 1322 Component Operation 1323 Stator Construction 1324 Capacitor Operation 1425 Title Slide (Starters) 1526 Starter Types 1527 Magnetic Switch / Solenoid 1529 Starter Drive Operation 1530 Title Slide (Operation) 1531 Magnetic Switch / Solenoid 1632 Title Slide (Oscilloscope Interpretation & Diagnostics) 1733 Oscilloscope CRT 1734 NSM (Main Menu 1) 1735 NSM (Main Menu 4) 1736 NSM 1737 NSM 1738 Lab Area39 Title Slide (Computer Terminology an Operation) 1840 Hardware 1841 Software 1842 Terminology 18

Slide SequenceSlide No. Description page No.

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43 Networking 1944 CPU Operation 1945 Title Slide (Troubleshooting Diagnosis of Intermittent Faults) 1946 Six Step Troubleshooting 1947 Intermittent Faults 2048 Select Monitor 2049 Lab Area50 Copyright 200151 The End

Slide SequenceSlide No. Description page No.


6June 2001

IntroductionThis Technicians Reference Booklet containsinformation pertaining to advanced automotiveelectrical technology, and the Subaru electricalsystem. It reviews solid state devices, operationand diagnosis of Subaru starting and chargingsystems, operation and diagnosis, computerterminology and operation, and thetroubleshooting and diagnosis of intermittentfaults. In addition, the use of the Select Monitoris also explained during the presentation of themodule and will be demonstrated during the labexercises.

The text and illustrations are derived from theclassroom lecture and slide presentationmaterial and are intended to reinforce previousclassroom instruction and lab participation.

Technicians Worksheets provided by yourinstructor will be completed during the "hands-on" Lab Work segments of the AdvancedElectrical Theory & Diagnosis Module. Alwaysrefer to the appropriate model year SubaruService Manual and the applicable servicebulletins for all specifications and detailedservice procedures.

Solid State DevicesThe charging circuit will be used for the purposeof explaining semiconductors (diodes andtransistors) and the functions of semiconductors.These principles may also be applied to othertypes of circuits.

Basic electrical terms for the study of advancedelectrical theory and diagnosis:1. Alternating current (AC) — an electric current

which constantly changes polarity frompositive to negative. (or an electric current thatreverses its direction regularly andcontinually).

2. Direct current (DC) — an electric currentwhich flows in one direction only.

3. Sine wave — a wave that alternately movesbetween a positive and a negative value overan equal length of time.

4. Square wave — a square or rectangular-

shaped wave that alternately assumes a "ON"or "OFF" mode. The length of the "ON" timecompared to the "OFF" time indicates a "dutyratio".

This booklet contains a Glossary of electricalterms for your reference. Refer to the Glossarywhen appropriate throughout the duration of thismodule.


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Diodes

We begin our study of advanced electrical theorywith an explanation of the construction andoperation of diodes.

Diodes are commonly constructed of one of twomaterials:

• Silicon• Germanium

These two materials possess the unique propertyof having exactly four electrons in the outervalence ring of their atoms. To create a diode,one of four impurities, (Gallium, Indium, Arsenic,or Antimony) may be combined with eitherSilicon or Germanium to form a new latticestructure. The maximum number of electrons thatcan reside in a valence ring is eight (8).

NOTE: THE PROCESS OF COMBININGIMPURITIES SUCH AS GALLIUM, INDIUM,ARSENIC, OR ANTIMONY WITH EITHERSILICON OR GERMANIUM IS CALLEDDOPING.

Lattice structure

Structural changes to the atoms

The impurities Gallium and Indium each havethree (3) electrons in the outer orbit (valence ring)of their atoms. When either of these impurities ismixed with Silicon or Germanium, (4 electrons),the result is a new atom which has sevenelectrons in the valence ring (4 + 3 = 7). Thissituation is equal to a deficiency of one electron(hole) in the valence ring. The result is that thenew material takes on a positive (+) charge.

Arsenic and Antimony each have five (5)electrons in their atom's outer orbit (valence ring).When either of these impurities is mixed withSilicon (or Germanium) the result is an atom withnine electrons, (5 + 4 = 9). Nine electrons cannotreside in a valence ring, and therefore isequivalent to one excess or "FREE" electron.This ninth electron rejected by the valence ringhas a negative charge.

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Negative charges are attracted to positivecharges at the barrier junction, when the properpolarity voltage is applied. When the negative andpositive charged atoms meet at the barrierjunction, the electrons will then move in a chainreaction toward the positive terminal of the diode.This is equal to current flow through the diode.

Diode polarity

The negative pole of a diode is called thecathode and the positive pole is the anode. Inthe center of the diode is the positive (+)/negative(-) junction (P/N junction).

This is also called a "barrier junction". The P/Njunction determines the maximum allowablecurrent flow of the diode and it is this featurewhich allows the diode to function as a one-wayswitch.

A silicon diode normally requires approximately0.7v to cause a current to flow in the normalforward bias mode. Forward bias means thepolarity of the input voltage will allow current toflow through the diode. However, if current flowis reversed, (reverse bias mode), the polaritycauses the semiconductor's barrier junction toresist current flow. It may require up to 1000 voltsto cause a current to flow through the diode inthe reverse bias mode. This is called the P.I.V.(peak inverse voltage) rating.

Exceeding the amperage rating of the diode may:

• Fuse the P/N junction, creating a shortcircuit. The diode will then act like a solidwire conductor, or

• Open the P/N junction creating an opencircuit through which no current may flow.

The automotive industry primarily uses silicondiodes because of their excellent heat tolerancecharacteristics.

Schematic/pictorial symbols

A line (mark) on the body of most diodes willalways identify the cathode or negative end ofthe diode for testing and installation purposes.

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Testing diodes

You may use an ohmmeter of a voltmeter to testthe operation of a diode.

1. Ohmmeter test• Connect the meter positive lead to the

cathode (-) lead of the diode and the meternegative lead to the anode (+) lead of thediode. The result should be highresistance meter reading, ex: 5k ohms ormore. This is due to the "unlike" chargesof the voltage source (ohmmeter) and thediode material. The electrons and "holes"are pulled to the outside ends of the diodecausing a large depletion region at the P/N junction. A low resistance readingwould indicate that the diode is "shorted",and requires replacement.

• If you now reverse the meter leadconnections, the result should be a lowresistance reading, ex 100 ohms or less.This is due to the "like" charges of thevoltage source (ohmmeter) and the diodematerial. The electrons and "holes" arerepelled (pushed) to the P/N junctionwhich allows current to flow. A highresistance reading indicates that the diodeis "open", and must be replaced.

NOTE: WHEN USING AN OHMMETER TOTEST A DIODE, MAKE SURE THE POWERIS TURNED "OFF", OR WHERE POSSIBLE,REMOVE THE DIODE FROM THE CIRCUIT.

2. Voltmeter test• The diode must in an operating circuit.

Connect the voltmeter leads to the diodeleads, (observe polarity). Refer to theappropriate wiring diagram to determinethe voltage that should be in the circuit. Inmost automotive applications this will beB+ voltage. The diode is "OK" when themeter readout is as follows:- Silicon diode — approx. 0.7 voltage

drop (dynamic resistance)- Germanium diode — Approx. 0.2

voltage drop (dynamic resistance)

The voltage drop reading always identifies thediode type. Any other reading indicates a circuitor diode defect, and further testing will byrequired.

If the meter readout voltage is equal to the circuitvoltage, the diode is open (all current is flowingthrough the voltmeter). When the meter readoutvoltage is equal to 0.0 volts, the diode is fused(shorted). All the current is flowing through thediode.

NOTE: A DIODE'S PERFORMANCE DOESNOT DETERIORATE WITH TIME OR USE.THEREFORE, WHEN TESTING, THE RESULTWILL EITHER BE "GOOD" OR "BAD",HOWEVER, IT IS POSSIBLE FOR A DIODE TOBE INTERMITTENTLY "GOOD" OR "BAD".

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Full wave rectification

A diode may be used to convert (rectify) ACvoltage to a pulsing DC voltage. Because of thediode's polarity, current is only allowed throughthe diode in one direction. Remember thatopposite polarity is denied conduction due to thehigh P.I.V. (peak inverse voltage rating) of thediode.

The negative pulses (opposite polarity) are thensent through an additional diode to the groundterminal of the battery. The result is single phase(DC) current.

Three phase current

Place three stator windings, positioned 120degrees apart, within a stator assembly. Duringeach rotation of the field, three (3) separatevoltage charges/pulses will be produced. Whenthe voltage is passed through six (6) diodes, (3positive and 3 negative), the result is three phaseDC current. The three phases overlap each otherwhich maintains a sufficient voltage level toproperly charge the battery.

LED/PSD

A light emitting diode (LED) is similar to a P/Ndiode. It can act as rectifier, converting current toinfrared or visible light. The color of the lightproduced by the LED is determined by the colorof the lens over the LED. Because the LED onlyrequires a very low operating current of 20 ma, ithas a long life which makes it most suitable forautomotive uses. When testing LED operation,Always check the operation of the component inwhich the LED is used. It is usually difficult totest LED operation by itself.

A photo sensitive diode (PSD) is similar to anLED, however, it will conduct current whenexposed to light. The PSD can also act as arectifier. As with the LED, it is better to test theoperation of the component than the PSD itself.

NOTE: AN LED AND A PSD ARE EMBEDDEDAS ONE UNIT IN THE DISTRIBUTOR ONSOME SUBARU MODELS, AND IS USED ASA CRANK ANGLE SENSOR.

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Zener diode

The zener diode allows reverse bias (voltage)at a predetermined level based on the impurityadded to the adhesive between the P and Nmaterials. This places the P.I.V. rating of thezener diode at a required specific value, i.e., 14volts. Remember that silicon diodes may gave aP.I.V. of a 1000 volts. This allows the zener diodeto modify current flow by switching the circuitrapidly :ON" and "OFF" when the appliedvoltage increases or decreases. The zener diodeis used in voltage regulators to preventovercharging or undercharging of the battery.

PNP transistor

A transistor is a solid state device used to controlcurrent flow. Two of many types of transistorswhich may be identified by their polarity/leaddesignation are:

• PNP = positive/negative/positive• NPN = negative/positive/negative

While a diode is formed by the joining of twospecially doped materials, a transistor is formedby the joining of three doped materials.

• Emitter material emits current• Collector material collects current.• Base material supplies the path used to

initiate or control current flow.

The base material is formed using a differentdoping process than the emitter/collector materialand is thus the opposite polarity of the emitter/collector material.

Operational control of a transistor is determinedby the polarity of the base material whichdetermines the polarity of the voltage suppliedto the base. Thus, a PNP transistor operates byflooding the base material with free electrons(negative polarity). This allows the transistor toact as a switching relay, initiating current flowfrom the emitter to the collector. One of manyapplications of a PNP transistor is in theelectronic ignition system.

NPN transistor

Construction and operation of the NPN transistoris similar to the PNP transistor. In this casehowever, the base material is flooded with holes(positive polarity) to control current flow from theemitter to the collector. The NPN transistor isoften used as an amplifier in audio systems andother solid state circuits. This is the transistorwhich has allowed the miniaturization ofelectrical circuits by eliminating bulky vacuumtube circuitry.

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Testing Transistors

PNP transistor testing

You may use an ohmmeter to test the operationof a transistor.1. Always use the diode testing scale of an

ohmmeter to test a transistor.2. Test the transistor an two diodes.

• First test the emitter to base (E-B)• Then test the collector to base (C-B)

3. The result will be "good" or "bad". Meterreadings will vary depending on transistortype.

Ohmmeter test (PNP)1. Connect the meter positive lead to the emitter

lead of the transistor.2. Connect the meter negative lead to the base

lead of the transistor.3. The result should be a LOW resistance

reading.• Example: 100 ohms or less

4. Reverse the meter lead connections.

5. The result should be a HIGH resistancereading• Example: 5 K ohms or more

6. Connect the meter positive lead to thecollector lead of the transistor.

7. Connect the meter negative lead to the baselead of the transistor.

8. The result should be LOW resistance.• Example: 100 K OHMS or LESS

9. Reverse the meter lead connections10.The result should be a HIGH resistance.

• Example: 5 K OHMS or MORE

11.Meter readings will vary depending on thetransistor type.

12.A final rest includes a continuity test betweenthe emitter and collector terminals of thetransistor. Results should equal infiniteregardless of meter polarity.

Ohmmeter test (NPN)1. Reverse the lead connections in the above

test steps.

NOTE: REVIEW THE TRANSISTOR LEADIDENTIFICATION CHART SHOWN IN THISTRB.

A voltmeter test of transistor operation is notpractical in most automotive applications.

NOTE: A TRANSISTOR'S PERFORMANCEDOES NOT DETERIORATE WITH TIME ORUSE.

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Alternators

Alternator components

The components of a Subaru alternator are:• Pulley• Front cover/bearing• Rotor (field coil)• Stator• Voltage Regulator• Brush assembly• Rectifier• Rear cover/bearing• Cooling fan

Alternator component operation

Because the field winding (rotor assembly) islighter in weight and therefore easier to rotate, itrotates inside a stationary stator. Alternatingnorth and south magnetic fields are created bybending the front and rear plates over the coil ina star-shaped interwoven type pattern.

Stator contruction

The standard stator design is a 3 phase "Y"configuration with three coils connected at oneend. The coil of the "Y" are spaced at 120 degreeintervals. Full wave rectification is accomplishedthrough the use of six diodes, (3 positive and 3negative). As the field coil rotates, current isinduced into each stator winding, charging thewinding. Negative (-) and positive (+) polaritiesare created at the ends of the stator winding. Eachstator winding end is connected to a respectivediode in the rectifier assembly. The charge ineach winding causes the diode to allow chargingcurrent to flow to the battery for that period ofrotation ONLY. As the field continues to rotate, itsequentially charges the remaining statorwindings, causing their respective diodes toallow charging current to flow to the battery.

Four phase rectification incorporates a fourthwinding which spaces the windings at 90degrees intervals. Four phase units use 8 silicondiodes, (4 positive and 4 negative). Theadvantages of four phase rectification are anincrease in current output and a reduction ofripple voltage output.

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Capacitor operation

The capacitor maintains stator voltage betweenphases by charging at peak voltage anddischarging as the phase voltage drops. This hasthe effect of smoothing the "ripple" voltageproduced by the phases of the alternator. Thecapacitor also reduces radio frequencyinterference (RFI).

Solid State Voltage RegulatorThe internal solid state type of voltage regulatorcontrols voltage within a specified range (usually14.1 - 14.8 volts). The regulator provides an "ON"and "OFF" voltage pattern to the field coil. Thefield coil is turned "OFF" by the regulator whenthe battery voltage reaches a preset level. Thisstops the alternator from charging. When thebattery voltage drops below the preset level, theregulator charges the field coil to the maximum.The "ON" and "OFF" threshold level isdetermined by a zener diode that is incorporatedinto the regulator assembly.

Alternator Testing PrecautionsDisconnect all connectors properly.

Do not ground circuits with tools.

Never lay tools on the battery.

Always disconnect the battery prior to alternatorreplacement.

Secure loose harness/wiring to prevent damagecaused during alternator removal/replacement.

When full-fielding the alternator, never exceed16.0 volts. Voltage levels in excess of thisspecification may cause damage to electricalsystem components.

Never disconnect the battery during an alternatortest.

An alternator performance test should only bemade with a serviceable battery.

Conduct an alternator performance test when anyof the following conditions are present:

• The battery is dead (discharged), butholds a charge when charged. Also, thebattery performance test indicates a goodbattery.

• The vehicle voltmeter indicates adischarging condition or the chargewarning light is illuminated during normalvehicle operation.

Conduct the alternator performance test inaccordance with the operator's instructions for thetest equipment you are using.

Conduct an alternator charging test, a voltageregulator test, and a diode/stator test. Comparethe results of the tests to the specifications listedin the appropriate MY Subaru Service Manual.Repair and or replace components as required.

Conduct a charging system requirements test inaccordance with the operator's instructions for thetest equipment you are using. Be sure to connectthe D-Check connectors so that the fuel pumpand other fuel system components operate.

Restore the D-Check and alternator connectionsto the normal operating condition.

Listed in the appropriate MY Subaru ServiceSubaru Starting Systems.

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StartersStarter Types

• Reduction Gear• Direct Drive

Starter components

The components of the starter assembly are:• Pinion (drive)/one-way clutch• Armature• Commutator• Field shoes• Brushes/brush holders• End caps/bushings

Magnetic switch/solenoid

The components of the magnetic switch/solenoidare:

• Pull-in winding• Hold-in winding• Plunger• Return spring• Shift lever• Starter motor contacts

OperationWhen the ignition switch is turned to the"START" position, battery voltage (B+) is allowedto energize the magnetic switch/solenoid pull-inand hold-on coils. The field created by the coilsmoves the plunger which in turn moves the shiftlever engaging the starter pinion with theflywheel. The movement of the plunger alsoactivates the starter motor switch contacts. Thisallows B+ voltage from the battery cable to flowto the starter motor through the magnetic switch.

The starter rotates the pinion which rotates theflywheel to crank the engine. When the engine"starts", the one-way clutch "freewheels" toprotect the starter armature and commutator froman "overspeed" condition.

When the ignition switch is released from the"START" to the "ON" position, this eliminates theflow of B+ voltage to the magnetic switch/solenoid which collapses the field. The plungerspring returns the plunger to its original positionmoving the shift lever which disengages thepinion from the flywheel. The plunger alsoreleases the switch contacts and the starter motorstops rotating.

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An occasional problem with starting systems isa defective hold-in winding in the solenoid. Inthis situation, the solenoid will "click" rapidly. Thisoccurs because the pull-in winding moves theplunger but the hold-in winding is not energized.Since no hold-in field is created and the pull-inwinding field is released as the start switch isengages, the plunger return spring returns theplunger to the pre-start position. This processrepeats and the plunger moves back and forthrapidly. This action will momentarily engage theflywheel, and occasionally may rotate theflywheel enough to start the engine.

NOTE: THESE SYMPTOMS ARE SIMILAR TOTHOSE CAUSED BY A DEFECTIVEBATTERY OR BATTERY CONNECTIONS.THEREFORE, A BATTERY PERFORMANCETEST, AND AN INSPECTION OF THEBATTERY CONNECTIONS MUST ALWAYSBE PERFORMED PRIOR TOTROUBLESHOOTING THE STARTERSYSTEM.

Starter/Solenoid Testing Procedures

Magnetic switch/solenoid

Use an ohmmeter to test the pull-in and hold-inwindings. Always refer to the appropriate MYSubaru Service Manual, Section 6-1.

Use a voltmeter to conduct a starter motor testfor intermittent operation. Complete the followingsteps:1. Connect the voltmeter leads to the starter

motor terminal and to a ground.2. By-pass the solenoid by connecting a jumper

cable from the solenoid B+ terminal to thesolenoid starter motor terminal. This spins thestarter, but dies not engage the magneticswitch/solenoid.

3. If there is a steady voltage reading the startermotor components are OH.• Brushes• Commutator• Armature

4. A variable voltage reading indicates aproblem in:• Brushes are arching• Commutator is dirty or has a defective

segment• Armature is open or has a shorted winding

Finally, be sure to test all cables using the voltagedrop method.

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Opcilloscope Testeing andDiagnosis

Oacilloscope CRT

Oscilliscope usage during diagnostics can helpwith finding intermittent or unusual problemconditions

An Oscilliscope function is included on theSelect Monitor. From the main menu cursor overitem "4. Oscilliscope." Press the "YES" key.

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This will give you one or two channel operation.

Press the F3 range key to adjust the voltage perdivision or cursor down to the TIME[s] and adjustthe seconds or milliseconds per division.

Many other features are included for the SelectMonitor Oscilloscope and your instructor willguide you through them in the lab section of thismodule.

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TerminologyBIT (binary digit) This is the smallest unit ofinformation in the binary system used by thecomputer. The computer uses binary numbersto build letters, numbers, and other charactersused to record and display information.

The only binary numbers generated and usedby the computer are either zero ("0") or one ("1").Zero equals power "OFF", and one equals power"ON". Switching the power "ON" and "OFF" tospecific circuits in the computer, codes theinformation that is entered or displayed. Itrequires 8 BITS or 8 binary digits to equal 1BYTE.

BYTE (binary element string)

A BYTE is equal to 1 character, such as the letter"a". Therefore a BYTE contains a combinationof eight "1's" or "0's" (BITS).

Example: 1 0 0 1 1 0 1 0

"K" = 1000 or kilo (as in metrics). This term isused to indicate toe amount of memory spaceavailable in a computer. If it has 32K BYTES,then it can store 32,000 characters in its memory.

Mega hertz (Mhz) This term defines theprocessing speed of the computer in millions ofcycles per second.

Computer Terminology andOperationComputer HardwareAutomotive computer hardware is the electronicand tangible componentry used for its operation.a. The CPU (central processing unit) is the area

in which all arithmetic and logic decisions arecalculated/computed.

b. The address register is similar to a file cabinet.It is where the computer sets up unique filelocations to store data in the memory.

c. The data register is used by the CPU to "read"and "write" information to/from the memoryfiles.

d. The ROM (read only memory) containsinformation that is programed into thecomputer during the manufacture of thecomputer. These operating commandscannot be changed or updated.

e. RAM (random access memory) is whereinformation is continually updated by theinputs from the various engine sensors. TheRAM is often called the "scratch pad" of thecomputer.

Computer SoftwareThe software consists of the programs and dataused by the computer to perform specific tasks.a. The PROM (programmable read only

memory) is information programed into thecomputer "chip". It contains the operatingcharacteristics of a specific model or enginefamily and can be added to the computerduring vehicle assembly to "fine-tune" vehicleoperation.

b. The EPROM (erasable programmable readonly memory) is similar to the PROM inoperation. Information can be:• Erased under ultra-violet light.• Reprogrammed to a new set of values.

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Handshaking

This term refers to the exchange ofpredetermined information that establishes aconnection between two or more computers.Without handshaking one computer would notbe able to understand another computer's datainput and vice-versa. The ROM's initiate theconnection while the RAM sections exchangeinformation. This process is also callednetworking.

Computer operation

The CPU sends an information request to theROM (memory) over the address buss line(connecting wires) to the address register. TheCPU then temporarily stores this information inthe CPU register while it compares theinformation to data stored in the RAM. The RAMdata is the inputs received by the computer fromthe various vehicle sensors.

When the data in the CPU register matches thedata in the RAM, no action is required. If the datain the CPU register does not match the data inthe RAM, the CPU generates a command signalto the appropriate device to alter vehicle orspecific component operation.

• Example: The O2 sensor voltage is toohigh and the fuel mixture is too rich. Theresponse is that the computer narrows thefuel injection pulse width.

If the data received is illogical to or from thecomputer, the computer generates a fault code.

All information, both to and from the CPU isresented almost simultaneously. However, it issynchronized by an internal clock. The clock alsocontrols the overall processing speed of thecomputer. Speed is measured in mega hertz

(Mhz), which equal millions of cycles per second.During networking the clock pulse will determinewhich computer is sending and which computeris receiving.

Troubleshootingn Diagnosis ofIntermittent Faults

Six Step TroubleshootingStep 1 — Verify the problem(s)Step 2 — Determine related symptom(s)Step 3 — Isolate the problemStep 4 — Identify the causeStep 5 — Repair/replaceStep 6 — Verify operation

NOTE: REFER TO THE SUBARU BASICELECTRICAL THEORY & DIAGNOSISMODULE, STEP 10 FOR ADDITIONALINFORMATION CONCERNING THE SIX STEPMETHOD.

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Intermittent FaultsThermal and Mechanical1. Thermal intermittent

• This type of problem occurs most often insolid state devices, connectors, switches,etc. Usually as the operating temperatureof a component increases, it causes anexpansion of the material which causesthe circuit to "OPEN". Current flow stops,the material cools and contracts, andrestores circuit operation.

2. Mechanical intermittent• This is caused by a component or

connection bending or shifting duringnormal vehicle operation.

• You may sometimes solve intermittentproblems using the following strategies:- Use a hair dryer to heat a component

or connection to simulate a severeoperating failure condition which youbelieve to be heat related.

- Mist water on a malfunctioningcomponent to determine if heat iscausing the problem. This simulatesa cooler operating temperature.

NOTE: DO NOT MIST COMPONENTS THATCANNOT TOLERATE MOISTURE. MAYCAUSE DAMAGE TO THE COMPONENTS.

- Use a component cooler which willquickly cool solid state componentswithout damage to the components.This method will identify intermittentdiode or transistor problemsbecause the component will usuallymalfunction when cooled quickly.

NOTE: DO NOT USE FREON WHICHCAUSES DAMAGE TO THE ENVIRONMENT!

- Jumper leads may be used tobypass connectors, switches, andcables to check an intermittentproblem.

NOTE: DO NOT UNDER ANY SITUATIONBYPASS A FUSE OR CIRCUIT BREAKER.SEVERE DAMAGE TO THE VEHICLE ANDPOSSIBLE PERSONAL INJURY MAYOCCUR.

Select Monitor Usage

Select monitor

The select monitor allows a review of the actualinformation processed by the computer. Forinstance, thermosensor input is displayed as theactual temperature of the coolant. You can thencompare the select monitor coolant temperaturereading with the actual coolant temperature todetermine possible sensor problems. (With a coldengine, the coolant temperature should be equalto the ambient air temperature).

Likewise, computer outputs may also bechecked: The select monitor will display thecomputer output to a system component such asthe fuel injector. This signal (injection pulse width)is displayed in milliseconds. We know thatthermosensor input will effect injection pulsewidth. With increased coolant temperature,injection pulse time (duration) should be reducedand the fuel mixture should become leaner. Withdecreased coolant temperature, injection pulsetime should increase and the fuel mixture shouldbecome richer. No change in the select monitorinjector signal could indicate thermosensor circuitproblems.

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NOTE: REFER TO SELECT MONITORINTROCUCTION VIDEO REFERENCEBOOKLET MSA5AV148B AND THEAPPROPRIATE MODEL YEAR SERVICEMANUALS FOR DETAILED SELECTMONITOR INFORMATION.


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Electrical Symbols


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Electrical Terms GlossaryAlternating Current (AC)an electric current which constantly changespolarity from positive to negative, (or an electriccurrent that reverses its direction regularly andcontinually).

Direct Current (DC)an electric current which flows in one directiononly.

Sine Wavea wave that alternately moves between apositive and a negative value over an equallength of time

Square Wavea square or rectangular-shaped wave thatalternately assumes a "ON" or "OFF" mode.The length of the "ON" time compared to the"OFF" time indicates a "duty ratio".

ResistanceProperty of an electrical circuit that tends toprevent or reduce the flow of current.

Dynamic ResistanceEffect of a resistor or resistance in a circuit.

Voltage DropThe difference in voltage between one point ina circuit and another, or the difference inmeasured voltage from one side of acomponent to the other side.

ResistorDevice that permits a predetermined current toflow aat a given voltage. Examples are a SPFIballast resistor and a 4EAT dropping resistor.

RheostatSee Variable resistor.

Variable Resistor/Rheostata device that adjusts the amount of resistancerequired. An example is a sliding contactresistor. The position of the contact determinesthe amount of resistance. The fuel sendingunits of a vehicle equipped with an analogdash use a variable resistor.

PotentiometerA resistive element with a sliding wiper contactthat is used in applications in which a divisionof resistance is required (such as a three-terminal adjustable resistive divider). Example:The throttle sensor on SPFI and MPFI fuelsystems.

SpliceJoining of two or more conductors at a singlepoint.

TerminalDevice attached to the end of a wire or cable tomake an electrical connection.

Ground/Chassis groundNegative side of a complete circuit. Inautomotive applications the negative side ofthe battery or any wire connected to theengine, frame, or body sheet metal.

RelayElectromagnetic switching device using lowcurrent to open or close a high-current device.

Solenoidan electromagnetic device consisting of atubular soil of wire containing a core thatmoves when the coil is energized. Movementof the core can open/close a circuit. A solenoidconverts electrical energy to mechanicalenergy.

FilamentA fine high resistance wire or thread whichglows and produces light when current isforced through it.

Diodesolid-state device that permits current to flow inone direction only; performs like a one-waycheck valve.

TransistorSolid-state semiconductor that is acombination current amplifier and switch(similar to a solenoid in the starter circuit or arelay in function). It uses low control current tochannel high current.

Capacitor (Condenser)Device used to store an electrical charge.


24June 2001

Notes:

Documents

Advanced Electrical Theory