fluke automotive

Application Note

Work safelyThis application note is intendedas a guide for the professionalmechanic. It describes some ofthe test procedures commonlyused by experienced technicians.However, some of the proceduresrequire you to take certain pre-cautions to avoid personal injuryand/or damage to equipment orvehicles. Fluke cannot anticipateall possible precautions that youmust take on all the differentvehicles for which this guide isapplicable. For this reason, youshould thoroughly familiarizeyourself with proper safety habits and take all precautionsdescribed in the vehicle’s repair manuals to avoid injury or damage.

Testing automotive systems with an analog/digital multimeterPerhaps the most important toolyou’ll use in troubleshooting autoelectrical systems is the multime-ter. The basic multimetermeasures voltage, current andresistance, while more elaboratemultimeters, such as the newFluke 88-V, have features thatcan check things such as frequency, duty cycle, pulsewidth, make diode tests, andeven measure temperature.

In this application note youwill find troubleshooting tech-niques using the high quality,affordable and popular line ofFluke analog/digital multimetersand automotive troubleshootingaccessories. Fluke’s analog/digital combination has distinctadvantages over either digital or analog meters alone, and the accessories are designed tomake your job easier and moreprofitable.

Automotive electrical diagnosis.Better diagnosis, faster repair.

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

Although automotive multime-ters with various capabilitieshave been around for years,many of them didn’t have thescales and functions required fortodays’ automotive applications.Hybrid, electric and fuel cellpowered vehicles have specialrequirements, ones met with thenew 88-V. Now that computersand their sensors are a part ofeveryday automobile trou-bleshooting, you need a truemultimeter to do the job.

The common analog type mul-timeter is not only inadequate, itcan damage delicate computercircuitry. Both analog meters andtest lights, due to their low inter-nal resistance (input impedance),draw too much power from thedevice they’re testing to be usedon computers. What’s more,many analog meters use 9V topower the resistance test, whichis enough to destroy sensitivedigital components.

The presence of voltage tells youthat the circuit is delivering elec-tricity to the component you’retesting.

The voltage reading tells youwhether the proper voltage isarriving at the component.

By measuring available voltageat a component, you can deter-mine whether the voltagereaching the device is adequate.

The voltage drop across acomponent tells you how much ofthe voltage is being consumed bythat component.

For example, if a relay has12.8 volts on the input side andonly 9.2 volts on the output side,the voltage drop is said to be 3.6volts. Remember that wire andconnections can also be consid-ered components and may causevoltage drops if faulty.

2 Fluke Corporation Beat the book

Over the last couple decades, adifferent type of multimeter hasevolved to solve problems notaddressed by analog multimeters.Digital multimeters (DMMs) havemuch higher input impedancethan analog meters, generally 1 Meg ohms (million ohms) to 10 Meg ohms. The high imped-ance means that the meter willdraw very little power from thecomponent under test. Besidesproviding more accurate meas-urements, this type of meter willnot damage sensitive computers.

The one problem with digitalreadouts has been that the num-bers displayed didn’t give muchinformation about whether thereading was increasing ordecreasing. You may have experi-enced the frustration of trying toread the constantly changingnumbers on digital exhaust gasanalyzers or scan tools.

Fluke has overcome the prob-lems associated with traditionalanalog and digital meters by providing a combination displaythat gives you the accuracy of adigital readout with the dynamicmeasurement capabilities of ananalog meter. Rather than addingnew meters to test every gizmothat comes along, one good multimeter will suffice.

Thinking about troubleshootingWhen troubleshooting electricalsystems, it’s important to use alogical process of deductive reasoning to solve the problem.This process is most importantsince you can’t see inside or dis-mantle the majority of electricalcomponents to tell whetherthey’re functioning, as you canwith mechanical devices.

Jumping to conclusions can beexpensive and time consuming.With well thought-out andorganized steps, you can usuallydetermine the source of the prob-lem the first time.

The key tool in this process isthe DMM.

Types of measurementsWhen troubleshooting auto-elec-trical systems, you measurevoltage, current and resistance.Probably the easiest and mostuseful measurement is voltage. Itcan answer these questions:

• Is voltage present?

• What is the voltage reading?

• What is the available voltage?

• What is the voltage dropacross a component or connector?

The Fluke 88-V Analog/DigitalMultimeter has several featuresthat make it well suited for automotive troubleshooters:Analog/Digital Display —Combined 33-segment analogbar graph and 6000-count digitaldisplay.Peak Min/Max — The PeakMin/Max function stores the low-est and highest measurementsmade by the meter as fast as 250 µS.Auto Hold — The meter display“freezes” a reading until you’reready to look at it.

Automatic Polarity and RangeSelection — The meter automati-cally selects the range andpolarity for the best possiblereading.Continuity Beeper — Audible“beep” tone provides easy testingfor continuity, shorts and diodetests.Rugged Construction — Toughplastic case survives the everyday hazards of working in a shop. Meter is backed by alimited lifetime warranty.

Volts

AC

Volts

DC

Mill

ivol

ts

Ohm

s

Cont

inui

ty

Dio

de T

est

Am

ps D

C*

Hz

% D

uty

Cycl

e

mS

Puls

e W

idth

RPM

**

Tem

pera

ture

Pres

sure

***

Vacu

um**

*

Min

/Max

Bar

Gra

ph


Troubleshooting with a Fluke analog/digitalmultimeterAutomotive electrical problemscan be divided into several cate-gories, according to the systemcausing the trouble. Rememberthat the real problem may exist inone system, while the symptomsyou’re testing appear in another.The systems covered in this bul-letin are:

• Charging System

• Starting System

• Fuel/Air System

• Ignition System

• Body Electric/EngineManagement/Cooling Systems

Many people won’t bring a carinto the shop until it won’t start,so for a great many failures that’sthe first symptom you’ll see. Thefirst challenge is to determinewhich system is the cause of the“no-start.”

Other failures result in chronicproblems of some sort, like arepeatedly discharged battery orhard starting when hot. Onceyou’ve decided on the systemmost likely to be the cause, youcan proceed with your tests,using Fluke analog/digital multi-meters.

Measurement Type

System/Component

Charging System

Alternators • • • • • •Computerized regulators • • • • •Connectors • • • •Diodes (ac ripple) • • •Diode rectifier • • •Regulators • • • • •Starting System

Battery • • • •Connectors • • •Interlocks (neutral safety switch) • • • •Solenoid • • • • •Starters • • • • •Fuel/Air System

Engine speed •Engine vacuum •Feedback carburetor • • • • •Fuel injectors (electronic) • • • • • •Idle air motors • • • • •Fuel system pressure •MAF sensor • • •MAP & BP sensors • • • •Throttle position sensors • • • •Igniton System

Coils •Condensors (capacitors) • • •Contact sets • • • • • • •Distributor cap •Ignition modules • • • •Body Electric

Compressor clutch • • • •Lighting circuits • • •Relay & motor diodes •Transmissions • • • •Engine Management

Computer temperature sensors • • • •Connectors • • • • •Hall-type sensor • • • • • • •O2 sensors • • • • •Oil pressure •Cooling Systems

Connectors • • • •Fan motor • • •Radiator • •Relays • • •Temperature switches • • • • •*Used with Fluke i410 or i1010 current clamp

**Used with the RPM80 Inductive Pickup accessory (included)***Used with optional PV350 Pressure/Vacuum Module


BatteriesCharging system problems oftencome to you as a “no-start” complaint. The battery will havedischarged and the starter won’tcrank the engine. The first step isto test the battery and charge it ifnecessary (Figure 1).

No-load testVoltage Percent charge

12.60 V to 12.72 V 100 %

12.45 V 75 %

12.30 V 50 %

12.15 V 25 %

Readings obtained at 80 °F (27 °C)

AlternatorsA DMM’s accuracy and digitaldisplay make regulator/alternatordiagnosis and adjustment easy.

RegulatorsFirst determine if the system hasan integral (internal) regulator,then whether it’s type A or B.Type-A has one brush connectedto battery + and the other brushgrounded through the regulator.Type-B has one brush directlygrounded and the other con-nected to the regulator.

Next, isolate the problem toalternator or regulator by bypass-ing the regulator (full-fielding).Ground Type-A field terminal.Connect Type-B field terminal toBattery +. If the system nowcharges, the regulator is faulty.Use a rheostat if possible.Otherwise, just idle the engine(lights on) so the voltage doesn’texceed 15 V.

Charging System

Load Test @ 1/2 CCA Rating8.5 V @ 0 °F (-18 °C)8.8 V @ 30 °F (-1 °C)9.4 V @ 50 °F (10 °C)9.6 V @ 70 °F (21 °C)

Figure 1. Measuring system voltageBleed the surface charge from the battery by turning on the head-lights for a minute. Measure the voltage across the battery terminalswith the lights off (see chart). When possible, individual cell specificgravity should be checked with a hydrometer. A load test should bedone to indicate battery performance under load. Voltage tests onlytell the state of charge, not the battery condition.

ZERO

A

600V 600A

CAT

AC/DC

CURRENTCLAMP 600V

OUTPUT:1mV/A

CATIII

i410

Figure 2. Verifying a good alternatorThe battery must be fully charged (see Figure 1). Run the engine andverify that no-load voltage is 13.8-15.3 V (check as in Figure 1). Next,load the alternator to rated output current with a carbon pile acrossthe battery. Run the engine @ 2000 RPM. Check the current with ani410 or i1010 current clamp.


Alternator ac leakageAn alternator generates currentand voltage by the principles ofelectromagnetic induction.Accessories connected to thevehicles charging system requirea steady supply of direct currentat a relatively steady voltagelevel. You can’t charge a batterywith alternating current, so itmust be rectified to direct current.

Figure 5. Alternator leakage currentTo check alternator diode leakage, connect the multimeter in serieswith the alternator output terminal when the car is not running.Leakage current should be a couple of milliamps at most; more often,it will be on the order of 0.5 milliamps. Use care when disconnectingthe alternator output wire; make sure the battery is disconnected first.Connect the meter, then reconnect battery.

Figure 4. Checking ripple voltageRipple voltage or (ac voltage) can be measured by switching your DMMto ac and connecting the black lead to a good ground and the red leadto the “BAT” terminal on the back of the alternator, (not at the battery).A good alternator should measure less than .5 V ac with the enginerunning. A higher reading indicates damaged alternator diodes.

ZERO

A

600V 600A

CAT

AC/DC

CURRENTCLAMP 600V

OUTPUT:1mV/A

CATIII

i410

Figure 3. Checking field currentWorn brushes limit field current, causing low alternator output. To test:load unit as in Figure 2 and measure field current with current clamp oruse 10 A jack on DMM. Readings range from 3 to 7 amps. On integralGM units: with alternator not turning, jump terminals together and con-nect both to Batt + with DMM in series set to measure 10 amps. Fieldcurrent should be between 2 and 5 amps, higher current with lowerbattery voltage. Control battery voltage by loading it with a carbon pile.

ZERO

A

1000A

600V 600A

CAT

AC/DC

CURRENTCLAMP

i1010 600V

OUTPUT:1mV/A

CATIII


Starting system troubles are oftenconfused with charging systemproblems. Many a dead batteryhas been replaced when the realcause was a faulty charging sys-tem. Be sure that the chargingsystem is functioning properlybefore you replace the battery.Make sure the battery is chargedand passes a load test, then lookfor resistance in the starter circuitif the engine still cranks slowly.

Starter currentInvestigate excessive currentdraw; check for worn-throughinsulation, a seized or tightengine, a faulty starter, etc. If thestarter turns the engine slowly,the current draw is not high, andthe battery is in good condition,check the resistance in the startercircuit.

Circuit resistanceOhm’s law (E = I x R) tells us thateven very low resistance in thestarter circuit will cause thestarter to turn slowly, because oflow voltage. For example: in asystem drawing 200 amps, 0.01ohms resistance in the startercable will cause a 2 volt drop involtage at the starter; 0.01 ohmsis too little for all but the mostexpensive and sophisticatedohmmeters to measure, butmeasurements of voltage dropwill indicate where there isresistance. See example of Ohm’sLaw on page 11.

Starting System

Figure 6. Measuring starter current drawDetermine how much current the starter is drawing by using Fluke’si1010 Inductive Current Clamp on the starter cable. This accessory willallow the multimeter to measure starter current up to 1000 amps.Check manufacturer’s specs for exact figures.

TestSolenoid

Test

Test

Test

Test

Test

Figure 7. Testing for excessive voltage dropDetermine if there is resistance in the circuit by measuring the voltagedrop across each connection and component in the starter circuitwhile cranking the engine. Measure the voltage drop between thebattery post and the connecting cable, the solenoid posts and thewires that attach to them, and across the solenoid itself. Also checkthe connection on the starter, alternator (feed and ground side) andthe ground strap connection to the engine block and body.


Ford BP/MAP sensorThe barometric pressure/manifoldabsolute pressure (BP/MAP) sen-sor is critical in determining fuelmixture and spark advance undervarying loads. Much like aThrottle Position Sensor, it mustprovide a smooth, gradualchange in output, or driveabilityproblems can occur. In someinstances, a BP/MAP sensor candeviate without setting troublecodes. To verify its operation, youneed to check its output over itsfull operating range.

Fuel pressureFuel pressure is important forboth performance and fuel effi-ciency. Maintaining proper fuelpressure under all operating con-ditions is the job of the fuelsystem.

The PV350 provides criticalfuel pressure readings on a multi-tude of fuel systems: carbureted,central point, throttle body injec-tion or multipoint injection. Use itwith the Fluke 88-V to check theoperation of fuel pressure regula-tors, fuel pumps and fuel pumpcheck valves.

Fuel pressures fall into twocategories: high and low. Centralpoint, or throttle body systemstypically use low pressure (10-15psi, 70-105 kPa). Most multipointsystems use a higher pressure(35-60 psi, 240-415 kPa). Lowpressure during hard accelerationcan indicate that a fuel filter isstarting to clog.

Fuel/Air System

HarnessConnector

JumperWires

To VacuumPump

SignalGround

BP/MAPSensor

Figure 8. Using dc-coupled Hz to check BP/MAP sensorsTo test the performance of a BP/MAP sensor, graph its frequency out-put at various levels of vacuum. Start with the sensor at 0” Hg (O cmHg) and read its frequency. Then note the frequency at each increaseof 1” Hg (2.5 cm Hg). When you plot these frequencies, they should bein a straight line. The frequency will decrease with an increase invacuum.

METRIC

ENGLISH

kPa psi

cmHg in Hg

OFF

PV350 PRESSURE / VACUUM MODULE

ZERO

Figure 9. Testing fuel system pressureTo test fuel pressure, use schrader hose adapter with the PV350 to tapinto the fuel rail. (If the vehicle doesn’t have a schrader valve port,ask your local tool supplier for the appropriate adapter.) Once you’vetaken your reading and before disconnecting the fitting, wrap a ragaround it to catch any fuel spray. The safest way to do this is to dis-able the fuel pump and run the engine until it dies. Crank the enginea few seconds longer until all fuel pressure is relieved.


Throttle Position Sensor(TPS)Throttle position sensors are acommon source of faults intoday’s on-board computers. ATPS is simply a variable resistorconnected to the throttle shaft.Some people think of it as areplacement for an acceleratorpump on throttle body or portfuel injected engines. But it ismuch more. It tells the on-boardcomputer how far the throttle isopen, whether it is opening orclosing — and how fast. As itsresistance changes, so does thevoltage signal returning to thecomputer. The TPS can be testedby watching either the voltage orresistance change, using the ana-log pointer on any Fluke DMM.

5V SupplyGroundSignal

Jumper Wires

Figure 10. Testing a throttle position sensorUse the Min/Max recording feature of the Fluke 88-V to check yourbase TPS setting at idle; to get the maximum reading, depress theaccelerator. By comparing these readings to those you get when youopen the throttle by hand, you can verify whether the throttle cableand/or linkage is properly adjusted to allow full throttle opening. If itisn’t, this may be the source of a problem with poor acceleration.


Ignition coilsFluke analog/digital multimeterswill measure from tenths of anohm (.01 Ω on the Fluke 88-VHigh Res Mode) up to 50 millionohms, making ignition tests easyto interpret. Analog meters usu-ally can’t measure less than 1ohm.

Spark plug wiresPlug wires should be checked ifyour scope indicates that theremay be a problem or if they’remore than a couple of years old.Not all wires indicate the datethey were manufactured. Due tothe heat of the spark plug insula-tor, a spark plug boot may bondto the spark plug. Pulling a sparkplug boot straight off the sparkplug can damage the delicateconductor inside the insulatedwire. Rotate the boot to free itbefore pulling it off.

If you suspect bad wires, testthe resistance of the wire whilegently twisting and bending it.Resistance values should beabout 10 KΩ per foot (30 kΩ permeter), depending on the type ofwire being tested; some may beconsiderably less. You shouldcompare readings to other sparkplug wires on the engine toinsure the accuracy of the test.

CondensersFluke analog/digital multimeterscan also be used for checkingautomotive capacitors (con-densers). The movement of thebar graph will show that theDMM is charging the condenser.You’ll see the resistance increasefrom 0 to infinity. Be sure toswitch the leads and check bothways. Also make sure to checkcondensers both hot and cold.

Ignition System

Figure 11. Measuring internal coil resistanceIf you suspect a malfunctioning ignition coil, check the resistance ofprimary and secondary windings. Do this when the coil is hot, andagain when it is cold. Also measure from the case to each connector.The primary windings should have a very low resistance, typicallyfrom a few tenths of an ohm to a few ohms. The secondary windingshave a higher resistance, typically in the 10 kΩ to 13 kΩ range. To getthe actual figures for a specific coil, check the manufacturer’s specs.But as a rule of thumb, primary windings range from a few tenths ofan ohm to a few ohms, and secondary windings may be 10 kΩ ormore.

Figure 12. Checking condenser leakageCheck for leaking condensers with the Ohms function. As the con-denser charges up, the resistance should increase to infinity. Anyother reading indicates that you should replace the condenser. If thecondenser is on the car, make sure the points are open. The Fluke 88-V has a capacitance test function that can be used as well.


Hall-Effect position sensorsHall-Effect position sensors havereplaced ignition points in manydistributors and are used todirectly detect crank and/or camposition on distributorless ignitionsystems (DIS), telling the com-puter when to fire the coils.

Hall-Effect sensors produce avoltage proportional to thestrength of a magnetic field pass-ing through them, which cancome from a permanent magnetor an electric current.

Magnetic position sensorsThe magnetic type of positionsensor is simply a magnet with acoil of wire wrapped around it.The clearance between thepickup and reluctor is critical. Besure to check it. Specs are usuallybetween 0.030" and 0.070" (0.8mm to 1.8 mm).

RPMThe RPM80 Inductive Pickupaccessory allows the Fluke 88-Vto measure engine RPM via thesecondary ignition impulses inthe spark plug wires. The meterfeatures a selection for DIS orconventional systems.

Hall EffectDevice Shields

Dist.Shaft

OutputSignal

12V

12V +

OpenClosed, connected to ground

0V

Insert knife bladeor steel feeler gaugebetween Hall device

and magnet

SwitchingTransistor

Gnd -

Check for outputpulses hereDist. Ref.

(Signal Out)

Connectwith jumpers

to battery

FixedPositionMagnet

Figure 13. Checking Hall-Effect sensorsCheck for reference voltage from battery at connector. Hall sensorsrequire power where magnetic sensors do not. To test sensor: connect+12 V from battery to power terminal, set DMM to measure volts andconnect it between signal output and ground. Insert feeler bladebetween sensor and magnet while watching for the bar graph tomove. Signal should vary from 12 V to 0 V.

Output Plug

SparkPlug

SparkPlugWire

ToDistributor

InductivePickup

Spark Plug Side

Figure 14. Measuring RPM with the RPM80 Inductive PickupThe RPM80 Inductive Pickup converts the magnetic field created bythe current in the spark plug wire to a pulse that triggers an RPMmeasurement. To measure RPM using the pickup, attach the probe toany accessible sparkplug wire and select the normal (2) or DIS (1) setting to read the correct RPM for the engine you are working on.Warning: Because the ignition system creates a shock hazard, turnoff the engine before connecting or removing the inductive pickup.

PickupCoil

Figure 15. Checking for pulses from magnetic distributor pickupDisconnect the distributor from the ignition module. Connect the DMMacross the pickup and set it to ac volts. When the engine is cranked,pulses should appear on the bar graph. If no pulses appear, it is likelythe reluctor wheel or the magnetic pickup is faulty. Use this techniquefor other magnetic position sensors too, such as VSS or ABS wheelspeed sensors. On GM cars, remove the distributor cap for access.


Locating current drainsCurrent drains, shorts and badgrounds are the cause of manyproblems. The cause of the prob-lem often seems to have nothingto do with the symptom. But,using a DMM, you can find thecause quickly without burning awhole box of fuses.

Current drains that run thebattery dead are often referred toas shorts, although they may notactually be short circuits. In fact,they may be related to Keep AliveMemory or K.A.M.

Shorts that blow fuses can befound using the same trou-bleshooting techniques used tofind current drains even thoughthe symptoms are different.

Caution: Each vehicle manu-facturer has a different procedurefor locating current drains. Usingthe wrong testing method willgive you erroneous results. Tomake sure you use the properprocedure, please refer to thevehicle manufacturer.

Example of Ohm’s LawIf you measure 0.5 V across theground connection in a startercircuit, and the starter draws 100 amps, calculate the resist-ance as follows:Ohm’s Law: E = I x R

0.5 V = 100 A x RSolve for R

R = 0.5 V100 A

Therefore R = .005 Ω.005 Ω is too much, so clean theconnection. .5 Volts tells you thesame thing — the connection isdirty or corroded.

Bad groundsHigh resistance among groundscan be among the most frustrat-ing of electrical problems. Theycan produce bizarre symptomsthat don’t seem to have anythingto do with the cause, once youfinally find it.

The symptoms include lightsthat glow dimly, lights that comeon when others should, gaugesthat change when the headlightsare turned on, or lights that don’tcome on at all.

With the new computer sys-tems, high resistance in groundwires and sensor leads can pro-duce all sorts of unpredictablesymptoms.

Apply silicone dielectric lubri-cant, available at radio supplystores, to connections before youassemble them. This will reducecorrosion.

Pay particular attention toground terminals in the vicinityof the battery, where acid speedscorrosion. Often a wire that iscorroded through except for afew strands will produce thesame symptom as a corrodedground connection.

Just looking at the insulatedconnector does not insure thatthe connection inside is good.Physically disconnect connectorsand use a wire brush or sandpaper to “shine” the metal connections.

How to use the Ohm’s Law trianglePut your finger over the value you want tofind. Multiply the remaining values if side-by-side; divide if one is over the other.

Voltage dropIn automotive circuits even thesmallest loss of voltage will causepoor performance. Set your Flukemultimeter in the mV or VDC set-ting and connect the meter +lead to the side of the devicenearer the battery + terminal andthe - lead to the side nearer thebattery - terminal or ground andengage the Min/Max function.Current must be flowing for themeter to register the voltage dropfound. This procedure is helpfulon components and connections(both on the + feed side and -ground side) except solenoids,which read battery voltage if youmeasure across them when theengine is being cranked.

Voltage drops should notexceed the following:200 mV Wire or cable300 mV Switch100 mV Ground0 mV to < 50 mV Sensor Connections0.0 V Connections

Body Electric / Engine Management / Cooling Systems

E

I R

E = I x RWhere:E = VoltsI = Current in AmpsR = Resistance in Ohms


Rear window grid defoggerFluke DMMs allow you to checkfor opens in the rear windowdefroster grid. The rear windowglass has a series of horizontalgrid lines made of a conductiveceramic silver compound that arebaked onto the inside surface ofthe glass. Terminals are solderedto two vertical conductors calledbus bars on each side of theglass; one serving as the feedconnection (battery voltage) andthe other as the chassis ground.Current flows through a relay tothe rear grid when both the igni-tion switch and the rear windowgrid switch are turned on, usuallydrawing about 20 amps. (A por-tion of the grid can be damagedby scratching the inside of thewindow usually by placing itemson the package shelf.) When thecircuit of any horizontal grid isinterrupted, no current will flowand that particular grid will notheat up. By determining wherethe open is, you can repair itwith a grid repair kit.

Duty cycleDuty cycle is the measurementmade of pulse width modulatedcircuits, such as a charcoal canis-ter purge solenoid. The higherthe duty cycle, the longer the on-time of that circuit. The higherthe on-time, the higher the flowrate, or purging of the canister.100 % duty cycle means thesolenoid is on all the time. 10 %duty cycle means that the circuitis energized only a small portionof the time. The ECU determineswhen to purge the canister andat what flow rate based uponsuch variables as engine temper-ature, how long the engine hasbeen running since startup, vehi-cle speed and other parameters.

Figure 16. Testing rear window grid with a DMMRun the engine at idle and set the rear window grid switch to “ON”.Connect the black lead from your DMM to one of the vertical “busbars” and the red lead to the other bus bar. With the meter set tomeasure dc volts, the display should indicate 10 to 14 volts; a lowerreading indicates a loose ground wire. With the black lead of theDMM grounded, touch each grid wire at its midpoint with the redlead. A reading of approximately 6 volts identifies a grid with noopens. A reading of 0 volts indicates the current path is brokenbetween the midpoint and the battery side of the grid. A reading of12 volts indicates that the circuit is open between the midpoint of thegrid line and ground.

Figure 17. Measuring duty cycle on a charcoal canisterTo measure the duty cycle of a solenoid, attach the red lead to thesignal wire and the black lead to a good engine ground. Select dutycycle and read the value directly.


Cooling systems/temperature measurementThe Fluke 88-V’s built-in temper-ature function makes it quick and easy to check engine coolingsystems for proper temperature,which is critical with today’scomputer-controlled engines. Youcan also check transmissions foroverheating, and heaters and airconditioning systems for properoperation.

With the Fluke 88-V’s 80BKbead thermocouple probe, youcan test thermostats and fanswitches without heating them inhot water on a hot plate. You getfaster, more accurate diagnosis ofelectrically controlled cooling sys-tems and can compare computerdata stream information withactual temperatures.

On many late model cars thecooling system is sealed; the onlyopening is in the expansion tank.Since it doesn’t have water circu-lating through it, you can’t makean accurate temperature meas-urement here. The only accuratetest is to measure the surfacetemperature of the upper tank atthe radiator inlet. With the Fluke88-V, it’s easy to do.

Figure 18. Testing for switch on-off temperatureCheck the operation of electric cooling fans by touching the radiatortank next to the temperature switch with the temperature probe tip.Note the temperature when the fan comes on, and again when it goesoff. Check your figures against factory specifications.

Figure 19. Testing for switch continuityCheck temperature-switch continuity with the Ohms function, whilethe switch is in place. With the switch connected and operating, testfor voltage drop across the switch and from the radiator to the bodyground, as described on page 11. Note: the temperature must beabove the “fan-on” temperature for the fan switch to be closed.

Fan goes off

Time

Fan comes on

195

180Tem

p°F

Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BD Eindhoven, The Netherlands

For more information call:In the U.S.A. (800) 443-5853 or Fax (425) 446-5116In Europe/M-East/Africa (31 40) 2 675 200 or Fax (31 40) 2 675 222In Canada (800) 36-FLUKE or Fax (905) 890-6866From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116Web access: http://www.fluke.com/automotive

©2004 Fluke Corporation. All rights reserved.Printed in U.S.A. 9/200 Pub-ID 10054-eng

Fluke.Keeping your worldup and running.


Fluke 112600 V measurement range

True-rms

10 amps continuous

Resistance and continuity

Frequency and capacitance

Three-year warranty

Fluke 73-331-segment analog bar graph

Automatic Touch Hold®

Auto and manual rangingDiode test/audible continuity beeperSleep modeLimited lifetime warranty

Fluke 78Volts, amps, continuity and resistance

Frequency and duty cycle

Direct reading dwell for 3, 4, 5, 6 and 8-cylinder engines

Temperature in °F or °C; thermocouple bead probe included

Min/Max recording

Precision analog bar graph

10 Megohm input impedance

Sleep mode

Protective holster with Flex-Stand™

Limited lifetime warranty

Fluke 87-V — True-rmsVolts, ohms, amps, continuity, diode test

250 µs Peak Hold

41⁄2-digit high resolution mode (20,000 counts)

Dual backlit display

Min/Max/Avg recording

Frequency and duty cycle measurements

Conductance and capacitance measurements

Sleep mode



Fluke 88-V — Average RespondingVolts, ohms, amps, continuity, diode test

250 µs Peak Hold

Milliseconds pulse width measurements

RPM measurements with RPM80 inductive pickup

Min/Max/Avg recording

Frequency and duty cycle measurements

LoOhms function and Input Alert™

Dual backlit display

Sleep mode



Fluke Multimeters and Accessories

i410 and i1010 DC/AC Clamp-On Current Probes

81T-IR Infrared TemperatureProbe

80TK Thermocouple Module

PV350 Pressure/VacuumModule

80PK-8 Pipe ClampTemperature Probe

80PK-1 General Purpose BeadProbe

80AK Thermocouple Adapter

TL82 Automotive Pin andSocket Adapter Set

TLK282 Deluxe AutomotiveTest Lead Kit

TP81and TP82 Insulation PiercingProbes

TP84 Oxygen Sensor PiercingProbe

TP88 Rigid Backprobe Pin Set

fluke automotive

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voltage reading

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testing automotive systems

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