Elec04 The Starting System
Contents
1. Overview All current Toyota models are fitted with PS starters Armature Surface Commutator Permanent and Interpolar Magnet Pai Erm TE Surface Commutator Armature TL623f415 4 16 TOYOTA Technical Training The Starting System PS Starter Construction Coil wires in PS type starters are square in cross section for more 2 compact winding and YA Round shaped greater output torque Conductor Wire Armature Conventional Starter PS Starter Brush Surface Commutator Armature Square shaped Conductor Fig 4 16 TL623f416 Electrical Circuit Diagnosis Course 623 4 17 Section 4 PS Starter Motors Armature coil wires The coil wires in a PS starter armature are Construction square in cross section e More compact winding than round cross section wires e Greater output torque Surface commutator The square shape of the armature conductors allow the surface of the armature to act as a commutator Field coils Conventional starters use field coils PS type starters use two types of permanent magnets instead e Main magnets e Inter polar magnets The two types of magnets are arranged alternately inside the yoke e Work together to increase magnetic flux e Allows shorter yoke PS Starter Construction PS type starters use two types of permanent magnets instead of field coils Armature Surface Commutator Permanent and Interpolar Magnets Armature Fig2. Start Fusible tch Link Switc Terminal 50 Fig 4 30 TL623f430c Electrical Circuit Diagnosis Course 623 4 35 Section 4 Test for excessive resistance in the starter control circuit with these steps 1 Connect tester or meter leads e Red lead to the positive battery terminal e Black lead to terminal 50 on the starter motor 2 Ona vehicle with an automatic transmission put the shift selector in Park or Neutral For a vehicle with a manual transmission depress the clutch pedal NOTE Do not crank the engine longer than 10 seconds at a time 3 Crank the engine and note the voltage reading e 1 2 volts or less is acceptable e More than 1 2 volts is an indication of excessive resistance 4 Measure the voltage drop across the ignition switch and the neutral start clutch start switch e 0 1 volts or less is acceptable e More than 0 1 volts is an indication of excessive resistance If you find excessive resistance perform these steps e Isolate the cause e Repair the fault e Re test the voltage drop 4 36 TOYOTA Technical Training The Starting System Testing the Testing the starter relay involves two steps starter Relay 1 Check for continuity with the relay de energized 2 Check for continuity with the relay energized Relay de energized 2004 Camry starter relay in this example e No continuity between pins 3 and 5 through the open contacts e Continuity between pins 1 and 2 through th
3. 4 17 TL623415 4 18 TOYOTA Technical Training The Starting System PS Starter With the ignition switch placed to the START position Operation 1 Current travels from the battery through the closed ST1 contacts of the Ignition Switch and the Park Neutral Switch through the coil of the ST Relay to ground 2 The ST Relay contacts close Ignition Switch to START To Ignition Coils Current from Ignition Switch ST1 contacts energizes the ST Relay coil ele Park Neutral n e e Position Switch Fig 4 18 TL623f418 Electrical Circuit Diagnosis Course 623 4 19 Section 4 3 Voltage is applied through the closed ST2 contacts of the Ignition Switch to the hold in and pull in coils of the starter ST Relay Energized To Ignition Coils With the ST Relay contacts closed voltage is applied to the pull in and hold in coils Position Switch 11 Junction Connector Fig 4 19 TL623f419c 4 20 TOYOTA Technical Training Starter Motor Turns at Slow Speed Current is present through the hold in coil to ground and through the pull in coil and the motor windings to ground The Starting System 4 Current is present through the hold in coil to ground and through the pull in coil and the starter motor windings armature and field coil to ground The voltage drop created by the pull in coil limits current through the motor windings and keeps motor speed low To Ignition Coils
4. Park Neutral Position Switch Starter Fig 4 20 TL623f420c Electrical Circuit Diagnosis Course 623 4 21 Section 4 Current Through Pull in Coil Stops With battery voltage applied to both sides of the pull in coil no current is present in the coil With the pull in coil energized the solenoid plunger moves the drive lever to mesh the pinion gear with the ring gear As the pinion gear engages the ring gear the magnetic switch closes With the magnetic switch closed voltage is applied directly from the battery through the magnetic switch to the pull in coil With voltage applied to both sides of the pull in coil no current is present through the coil The magnetic switch is now held closed by the magnetic force of the still energized hold in coil To Ignition Coils ark Neutral osition Switch Junction Fig 4 21 TL623f421 4 22 TOYOTA Technical Training Pinion Gear Engaged with Ring Gear With the magnetic switch closed there is a large current directly from the battery through the motor windings The Starting System Current is now present from the battery through the closed magnetic switch and the motor windings to ground This current is not limited through the pull in coil so it drives the starter motor with greater speed and torque To Ignition Coils Position Switch FL Main 3 OW Junction Connector TL623f422c Electrical Circuit Diagnosis Course 62
5. This happens any time the pinion shaft tries to turn faster than the clutch housing Engine Starting The clutch housing armature and pinion gear turn together Clutch Housing Roller Springs Turns with Armature a Springs Pinion Relaxed Shaft Inner Race Wedged Rollers Pinion Gear Drives Ring Gear Fig 4 06 TL623f406c Electrical Circuit Diagnosis Course 623 4 7 Section 4 Engine Started The clutch housing and the armature turn together The ring gear drives the pinion gear The pinion shaft is disengaged from the clutch housing Springs Pinion Shaft Compressed Disengaged from Clutch Housing Pinion Gear Driven by Ring Gear 4 8 TOYOTA Technical Training Springs Compressed Pinion Shaft Disengaged from Clutch Housing Fig 4 07 TL623f407c The Starting System Ignition Switch The ignition switch incorporates contacts to provide B to the starter The relay energizes the starter magnetic switch when the driver turns the ignition key to the START position Ignition Switch With key to START position B is applied to OLock Ignition the starter motor Oacc Switch F OON Starter Fusible Park Neutral Link Position Magnetic Switch Fig 4 08 TL623f408c Electrical Circuit Diagnosis Course 623 4 9 Section 4 Park Neutral The park neutral position switch prevents operation of the starter Position Switch motor unless the shift le
6. 1 T623f411 4 12 TOYOTA Technical Training The Starting System Gear Reduction Ignition switch in ST rter ration Planer operatio 1 Current travels from the battery through terminal 50 to the hold in and pull in coils Then from the pull in coil current continues through terminal C to the field coils and armature coils 2 Voltage drop across the pull in coil limits the current to the motor keeping its speed low 3 The magnetic switch plunger pushes the pinion gear to mesh with the ring gear 4 The screw spline and low motor speed help the gears mesh smoothly Ignition Switch to ST The plunger pulls the drive lever which moves the pinion gear into engagement with the ring gear Hold in Coil Current Flow Terminal 50 Armature Fig 4 12 TL623f412 Electrical Circuit Diagnosis Course 623 4 13 Section 4 Pinion and ring gears engaged 1 When the gears are meshed the contact plate on the plunger turns on the main switch by closing the connection between terminals 30 and ss O iad 2 More current goes to the motor and it rotates with greater torque 3 Current no longer flows in the pull in coil The plunger is held in position by the hold in coil s magnetic force Ignition Switch to ST Cont The magnetic switch closes and current from the battery drives the starter motor directly Motor Armature Pinion Terminal C Terminal 30 Cu
7. 3 4 23 Section 4 With the engine started and the ignition switch released to the ON or IG position 9 Voltage is removed from the Ignition Switch ST contacts and applied to the IG contacts Current is present through the IG2 contacts to the ignition coils 10 Current through the hold in coil stops Current through the pull in coil reverses direction and flows from the battery through the magnetic switch the pull in coil and the hold in coil to ground With current through the pull in coil reversed the magnetic fields of the pull in and hold in coils cancel each other out 11 A return spring pulls the solenoid plunger and the drive lever back The pinion gear disengages from the ring gear The magnetic switch opens Current through the starter motor stops Ignition Switch Released to ON To Ignition Coils Current is no longer present and the pinion gear releases from the ring gear Ignition SW CA LP ote Park Neutral Position Switch Connector Fig 4 23 TL623f423c 4 24 TOYOTA Technical Training The Starting System Diagnosis The starting system requires little maintenance The battery should be and Testing fully charged and connections kept clean and tight Diagnosis of starting system problems is usually straightforward Problems may be electrical or mechanical The Starting System Troubleshooting chart lists the most common starting system problems the possible causes and recommend
8. Course 623 4 33 Section 4 Magnetic Switch NOTE NOTE Magnetic Switch Meter connected to measure voltage drop This test measures the voltage drop across the magnetic switch Starters with planetary gear reduction do not have a magnetic switch 1 Connect the tester or meter leads e Red lead to starter terminal C e Black lead to starter terminal 30 Do not crank the engine longer than 10 seconds at a time 2 Crank the engine and note the voltage reading e 0 3 volts or less is acceptable resistance e More than 0 3 volts is excessive resistance If you find excessive resistance perform these steps e Isolate the cause e Repair the fault e Re test the voltage drop A faulty magnetic switch could cause excessive resistance Neutral Start Fusible Switch Link Terminal 30 Fig 4 29 TL623f429c 4 34 TOYOTA Technical Training The Starting System Voltage Drop Tests Excessive resistance in the starter control circuit can reduce the Starter Control voltage available to the magnetic switch Symptoms of excessive Circuit voltage include the following e Pinion gear does not engage e Pinion gear engages only partially There are several areas where excessive resistance can occur e ST contacts of the ignition switch e Neutral start switch clutch start switch e Circuit wiring and connections Starter Control Circuit Voltage drop testing can 0 1V find excessive resistance or les Neutral
9. High resistance in the starter motor circuit can Circuit e Reduce starter motor current e Cause slow cranking Preparation Prepare the tester and the vehicle with these steps 1 Disable the fuel or ignition system so engine will not start while cranking NOTE For most Toyota vehicles you can pull the Electronic Fuel Injection EFI fuse or relay to prevent engine start 2 Set the VAT 40 volt selector to EXT 3 volts If you re using a DMM select a low voltage scale 3 Connect the VAT 40 or DMM leads to measure voltage drop for the following Battery post to cable Battery cable to starter Starter relay to starter PS type Starter case to cable e cable to battery post Terminal C to terminal 30 gear reduction type Battery to terminal 50 gear reduction type Normal voltage drops in the starting system are in the range of 0 2 volts to 0 5 volts TOYOTA Technical Training The Starting System Battery Positive This test measures the voltage drop across the positive battery post to Cable the cable and the connections at the battery and the starter NOTE Do not crank the engine longer than 10 seconds at a time Crank the engine and note the voltage reading e 0 5 volts or less is acceptable resistance e More than 0 5 volts is excessive resistance If you find excessive resistance perform these steps e Isolate the cause e Repair the fault e Re test the voltage drop Excessive resistanc
10. Section 4 The Starting System Starter The starter motor drives the engine through a pinion gear that engages the ring gear on the flywheel Fig 4 01 TL623f401 Starting System The starting system Overview Uses a powerful electric motor to drive the engine at about 200 RPM fast enough to allow the fuel and ignition systems to operate e Drives the engine through a pinion gear engaged with a ring gear on the flywheel e Disengages as soon as the engine starts Electrical Circuit Diagnosis Course 623 4 1 Section 4 Starting System These components make up a typical Toyota starting system Components Starting System Components Automatic Transmission These components make up a typical starting system automatic transmission e Starter motor Magnetic switch Over running clutch Ignition switch contacts Park neutral position A T or clutch start M T switch Clutch start cancel switch on some models Starter relay Ignition Starter Switch Relay To Engine Control Park Module ECM Neutral UCA Position nj o Switch Starter Magnetic Switch Wie Fig 4 02 TL623f402 4 2 TOYOTA Technical Training Starting System Components Manual Transmission These components make up a typical starting system manual transmission The Starting System Ignition Switch Clutch Start Switch Starter Magnetic Switch Fig 4 03 L623f403 Electr
11. The Starting System Clutch Start Troubleshoot the Clutch Start Cancel Switch with these continuity and Cancel Switch operational checks Continuity Use a digital multimeter to confirm that there is no continuity between these terminals e land2 e land3 e 2and3 Replace the switch if you find continuity between any of these pairs of pins Operational Connect a battery across pins 1 and 3 Use a digital multimeter to check for continuity as follows e no continuity between pins 1 and 2 with switch OFF e continuity between pins 1 and 2 with switch ON Replace the switch if either of these tests gives a continuity result different from the specification Electrical Circuit Diagnosis Course 623 4 41 Section 4 Clutch Start Cancel Switch Switch must be tested Continuity Checks with continuity checks and operational checks T623f435c 4 42 TOYOTA Technical Training
12. e could be caused by any of these e Damaged battery cable e Poor connection at battery or starter terminal e Defective magnetic switch Battery Positive Cable Meter connected to measure voltage drop Neutral Start Fusible Switch Link Fig 4 27 TL623f427c Electrical Circuit Diagnosis Course 623 4 31 Section 4 Battery Negative Cable NOTE This test measures the voltage drop across the negative battery cable the connections at the battery and the starter and the connection to ground through the starter motor case 1 Connect the tester or meter leads e Red lead to the starter motor housing e Black lead to negative terminal of the battery Do not crank the engine longer than 10 seconds at a time 2 Crank the engine and note the voltage reading e 0 2 volts or less is acceptable resistance e More than 0 2 volts is excessive resistance If you find excessive resistance perform these steps e Isolate the cause e Repair the fault e Re test the voltage drop Excessive resistance could be caused by any of these e Damaged battery cable e Poor connection at battery or starter terminal e Poor connection between the starter case and the vehicle chassis could be caused by a loose motor mount 4 32 TOYOTA Technical Training The Starting System Battery Negative Cable Meter connected to measure voltage drop Starter Motor Housing Fig 4 28 TL623f428c Electrical Circuit Diagnosis
13. e relay coil NOTE To energize the relay connect two jumper wires e Battery positive to pin 1 e Battery negative to pin 2 Relay energized e Continuity between pins 3 and 5 through the closed contacts If any of these checks do not produce the specified result replace the relay Starter Relay Tests Relay De energized Relays must be tested for continuity in both states energized and de energized Relay Energized Fig 4 31 TL623f431 Electrical Circuit Diagnosis Course 623 4 37 Section 4 Ignition Switch Check the ignition switch both mechanically and electrically and Key Mechanically Switch should turn smoothly without binding Binding may mean problems with the lock cylinder or the electrical contacts Check the ignition key for excessive wear or rough surfaces Electrically Disconnect the battery ground cable and check for continuity through the ST contacts Refer to the appropriate service manual for wiring details Ignition Switch Switch must operate i x smoothly and provide the f To Ignition Coils correct current path Fig 4 32 TL623f432c 4 38 TOYOTA Technical Training The Starting System Park Neutral Adjust the park neutral position switch if you can operate the starter Position Switch with the gear selector in any position other than Park or Neutral Adjust the switch as follows l 2 3 4 ar Loosen the switch retaining bolt Disconnect the switch electr
14. ed actions to resolve the problem Begin with a thorough visual inspection If this fails to turn up the possible cause several tests are available to help you find the problem e Starter motor current draw test e Voltage drop tests e Operational and continuity tests e Starter motor bench tests Electrical Circuit Diagnosis Course 623 4 25 Section 4 Starting System Troubleshooting Chart Symptoms Engine will not crank Engine cranks too slowly to start Starter keeps running Starter spins but engine will not crank Possible Cause Dead battery Melted fusible link Loose connections Faulty ignition switch Faulty magnetic switch relay neutral start switch or clutch switch Mechanical problem in engine Problem in theft deterrent system Weak battery Loose or corroded connections Faulty starter motor Mechanical problems with engine or starter Damaged pinion or ring gear Faulty plunger in magnetic switch Faulty ignition switch or control circuit Binding ignition key Faulty over running clutch Damaged or worn pinion gear or ring gear Action Needed Check battery state of charge Replace fusible link Clean and tighten connections Check switch operation replace as needed Check and replace as needed Check engine Check repair manual for system tests Check battery and charge as needed Clean and tighten connections Test starter Check engine and starter replace worn out part
15. ical Circuit Diagnosis Course 623 4 3 Section 4 Starter Motor Toyota vehicles are fitted with one of two types of starter motors e Gear reduction e Planetary Reduction Segment PS Starter Motor The Gear Reduction starter is a compact lightweight unit with high torque capacity Posegi rmature Reduction E dez W Pinion ONS D Terminal 30 Over running Plunger Clutch Fig 4 04 TL623f404c Gear Reduction The gear reduction starter motor contains the components shown This Starter Motor type of starter has a compact high speed motor and a set of reduction gears While the motor is smaller and weighs less than conventional starting motors it operates at higher speed The reduction gears transfer this torque to the pinion gear at 1 4 to 1 3 the motor speed The pinion gear still rotate faster than the gear on a conventional starter and with much greater torque cranking power 4 4 TOYOTA Technical Training The Starting System The reduction gear is mounted on the same shaft as the pinion gear Unlike the conventional starter the magnetic switch plunger acts directly on the pinion gear not through a drive lever to push the gear into mesh with the ring gear This type of starter was first used on the 1973 Corona MKII with the 4M six cylinder engine It is now used on most 1975 and newer Toyotas Ratings range from 0 8 KW on most Tercels and some older models to as high as 2 5 KW on the diesel Co
16. ical connector Set the gear selector to the Neutral position Connect an ohmmeter across the switch contacts refer to the appropriate service manual for wiring details Adjust the switch to the point where the ohmmeter shows continuity Set the gear selector to Park confirm that there is still continuity through the switch Set the gear selector to any position other than Park or Neutral Confirm that there is no continuity through the switch Park Neutral Position Switch Switch may need adjustment if ignition switch operates starter with gear selector in any position other than Park or Neutral Neutral Basic Line Connector Groove Fig 4 33 TL623f433 Electrical Circuit Diagnosis Course 623 4 39 Section 4 Clutch Start Switch Adjust the Clutch Start Switch using the appropriate service manual The procedure involves checking clutch pedal height and free play in the switch Use a digital multimeter to check continuity through a properly adjusted switch Pedal depressed There should be continuity through the switch with the clutch pedal depressed Pedal released There should be no continuity through the switch with the clutch pedal released Clutch Start Switch There should be no continuity through the switch with the clutch pedal released 10 0 0 5 mm Clearance greater than 1 mm 0 394 0 020 in with clutch depressed Fig 4 34 TL623f434c 4 40 TOYOTA Technical Training
17. ition with a battery analyzer Charge if switch set to ON and the clutch switch or needed neutral start switch closed Check the electrolyte level and top up If you suspect the ignition switch is faulty with distilled water if needed use a remote starter switch and jumper wire to confirm starter operation STARTER e Inspect the starter motor for external PARK NEUTRAL CLUTCH START SWITCHES damage to the case or wiring including e Conduct a voltage drop test to verify the magnetic switch circuit corroded proper operation max 0 1 V drop terminals and loose connections e Check for loose mounting hardware Tighten as needed Electrical Circuit Diagnosis Course 623 4 27 Section 4 Current Draw Test The starter current draw test effectively checks the entire starting system A special purpose tester connects to the battery to measure starting current and cranking voltage The procedure shown here applies to the VAT 40 and with some minor differences the VAT 60 1 Make a visual inspection of the battery electrolyte and battery cables 2 Turn off all electrical accessories and lights in the vehicle set ignition switch to OFF 3 Disable the fuel or ignition system so the engine will not start while cranking 4 Connect the tester in this sequence e Red lead to positive battery terminal e Black lead to negative battery terminal e Current probe on negative battery cable Starter Current Draw Test Batter
18. rolla Camry and Truck The cold weather package calls for a 1 4 KW or 1 6 KW starter while a 1 0 KW starter is common on other models The gear reduction starter is the replacement starter for most conventional starters Electrical Circuit Diagnosis Course 623 4 5 Section 4 NOTE Older Toyota models use conventional type starters This type of starter drives the pinion gear directly The pinion gear turns at the same speed as the motor shaft These starters are heavier and draw more current than gear reduction and PS type starters Conventional Starter Motor 4 6 Conventional type starter motors drive the pinion directly Magnetic Switch Shift Lever Over running Clutch Armature Pinion Gear Fig 4 05 TL623f405c TOYOTA Technical Training The Starting System Over running Both conventional and gear reduction starter motors are fitted with a Clutch one way over running clutch The clutch prevents damage to the starter when the engine starts Clutch Operation 1 During engine start the starter pinion gear drives the engine s flywheel ring gear 2 Once the engine fires the ring gear almost instantly begins to turn faster than the starter pinion gear Over speeding would damage the starter motor if it were not immediately disengaged from the pinion gear 3 The clutch uses its wedged rollers and springs to disengage the pinion shaft from the clutch housing which turns with the motor armature
19. rrent Flow Fig 4 13 TL623f413c 4 14 TOYOTA Technical Training The Starting System Ignition switch in ON 1 Current no longer present at terminal 50 but the main switch remains closed to allow current from terminal C through the pull in coil to the hold in coil 2 The magnetic fields in the two coils cancel each other and the plunger is pulled back by the return spring 3 The high current to the motor is cut off and the pinion gear disengages from the ring gear 4 The armature has less inertia than the one in a conventional starter Friction stops it so a brake is not needed Ignition Switch ON Current through the starter relay stops The pinion gear disengages from the ring gear and the magnetic switch opens Motor Armature Pinion N e Ring Gear Current Flow Terminal Terminal 30 y ey Fig 4 14 TL623f414c Electrical Circuit Diagnosis Course 623 4 15 Section 4 PS Starter Motors All current Toyota models are fitted with Planetary Reduction Segment Overview Conductor PS starters Planetary reduction allows the starter motor to operate at a higher speed than a conventional starter e The reduction gear set reduces the pinion gear speed compared to motor shaft speed e Higher motor speed yields greater torque Segment conductor type starters incorporate several design improvements e More compact e Lighter weight e Greater output torque PS Starter
20. s Check gears for wear or damage Test starter pull in and hold in coils Check switch and circuit components Check key for damage Check over running clutch for proper operation Check gears for damage and wear replace as needed Starter does not engage disengage properly Faulty magnetic switch Damaged or worn pinion gear or ring gear 4 26 TOYOTA Technical Training Check and replace as needed Check gears for damage and wear replace as needed Fig 4 24 The Starting System Visual Inspection A visual inspection of the starting system can save you time and effort by uncovering obvious or simple and easy to fix problems Ulol E The battery contains sulfuric acid Take precautions to avoid possible injury or damage to the vehicle e Remove rings wristwatch and any other jewelry that might contact the battery terminals before beginning the inspection e Wear safety glasses and protective clothing to protect yourself from acid Include these components in your inspection e Battery e Starter e Ignition switch e Park neutral position or clutch start switch Visual Inspection BATTERY IGNITION SWITCH e Inspect the battery for external damage e Inspect the ignition switch for loose to the case or the cables corroded connections and damaged wiring terminals and loose connections Confirm that the battery voltage is available Check the battery s state of charge at the magnetic switch with the ign
21. ver is in Park or Neutral The switch contacts Automatic are in series with the starter control circuit Transmission Park Neutral Position Switch 4 10 The switch closes with the shift lever in Park or Neutral Fusible Link TOYOTA Technical Training OLOCK Ignition Oacc Switch pee OON 8 Park Neutral Position Switch Starter Relay Magnetic Switch Fig 4 09 TL623f409c The Starting System Clutch Start For manual transmissions the clutch start switch performs the same Switch Manual function as the park neutral position switch The clutch start switch Transmission opens the starter control circuit unless the clutch is engaged Clutch Start Switch Otock Ignition The switch closes when Oacc Switch the clutch pedal is pe OON depressed Magnetic SN Fig 4 10 L623f410c Electrical Circuit Diagnosis Course 623 4 11 Section 4 Clutch Start In some off road situations it is advantageous to start a manual Cancel Switch transmission vehicle while in gear with the clutch engaged The driver controlled safety cancel switch allows the driver to bypass the clutch start switch to make this possible This feature is only available on some models Clutch Start Cancel Switch Otock Ignition This switch lets the Oacc Switch driver bypass the clutch p gt OON start switch for off road operations Fusible Link Clutch Start Cancel Switch Magnetic Switch Fig 4 1
22. y tester is connected to measure starter current and battery voltage Fig 4 26 TL623f426c 4 28 TOYOTA Technical Training The Starting System 5 For VAT 40 set the voltage selector to EXT 18 volts 6 Without cranking the engine note the voltage reading e Should be at least 12 6 volts e Recharge the battery before proceeding if the voltage is below 12 6 volts 7 Crank the engine and observe the voltage and current readings e Engine speed should be between 200 and 250 RPM while cranking e Voltage should be at or above the service specification refer to appropriate repair manual e Current should be at or below the service specification refer to appropriate repair manual 8 When finished with the test disconnect the tester leads and enable the fuel or ignition system replace fuse or relay NOTE For most Toyota vehicles you can pull the Electronic Fuel Injection EFI fuse or relay to prevent engine start You can connect the current probe to either battery cable Just be sure to orient the arrow on the probe correctly The arrow should point down away from the battery for the positive cable the arrow should point up toward the battery for the negative cable Do not crank the engine longer than 10 seconds at a time Electrical Circuit Diagnosis Course 623 4 29 Section 4 Voltage Drop Tests 4 30 Voltage drop tests can find excessive resistance in the starting system Starter Motor
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