33 Chapter Charging System Diagnosis, Testing, and Repair

Objectives After studying this chapter, you will be able to: Inspect a 12-volt and high-voltage (HV) charging system to locate obvious troubles. Diagnose 12-volt and HV charging system troubles. Test 12-volt charging system and HV power control module output with a voltmeter, load tester, or scope.

Objectives Remove, test, repair, and replace an alternator. Adjust an alternator belt. Correctly answer ASE certification test questions on charging system service.

12-Volt Charging System Diagnosis 12-volt charging system has only two major parts Alternator Regulator Troubleshooting can be difficult Sometimes another system’s fault Bad starting motor, defective battery, computer failure, or faulty wiring Will appear to be caused by charging system problems

12-Volt Charging System Diagnosis (Cont.) There are four common symptoms Dead battery Overcharged battery Abnormal noises Indicator shows problem

Preliminary Inspection Visually inspect charging system parts Check for battery-related problems Loose battery cables Discharged battery Corroded terminals Low water level Damaged battery case Make sure belt tension is adjusted to specifications

Preliminary Inspection (Cont.) Check condition of alternator drive belt Look for Cracks Glazing Grease Oil contamination Deterioration

Preliminary Inspection (Cont.) Check for Loose or corroded electrical connections Shorted wires Missing insulation Wiring problems Check electrical connections on back of alternator Wiggle wiring harness from alternator to firewall or ECM while engine is running

Preliminary Inspection (Cont.) With engine running, listen closely for abnormal noises Use stethoscope to listen for Dry, noisy alternator bearings Grinding Worn, dry bearings Whining Leaking diodes or overcharging Any other unusual sounds

Scanning 12-Volt Charging Systems Connect scan tool to aid in troubleshooting Scan tool will display Charging voltage Battery temperature Other data useful in finding problems Capabilities vary with each model

12-Volt Charging System Precautions Disconnect battery before removing any charging system component Disconnect battery before connecting it to charger Never reverse polarity Connecting battery or jumper cables backward can lead to serious electrical damage

12-Volt Charging System Precautions (Cont.) Do not operate alternator with output wire disconnected Never short or ground any charging system terminal Unless instructed to do so by shop manual

12-Volt Charging System Tests Charging system output test Regulator bypass test Scope testing Circuit resistance tests

12-Volt Charging System Output Test Connect tester leads, as described by manufacturer Clip inductive amps pickup around insulation on negative battery cable Set load tester controls to proper positions and values Attach vent hose to exhaust and start engine

12-Volt Charging System Output Test (Cont.) Rotate load control on tester until ammeter displays alternator’s rated amperage Do not exceed alternator’s output rating in amps Do not let voltage drop below full battery voltage of 12.6 volts Note alternator output current at 12.6 volts Turn off load control and evaluate readings

Regulator Bypass Test Quick and easy way to determine if alternator, regulator, or ECM to alternator is faulty If rear of alternator has test tab, short it on end frame When tab is shorted, alternator should produce maximum output

Regulator Bypass Test (Cont.) With some vehicles, jumper wire must be used to connect battery and field terminals On modern charging systems, you may have to disconnect and ground a specific wire on back of the alternator to full-field rotor winding ECM normally grounds this wire through power transistor to produce maximum voltage

Regulator Bypass Test (Cont.) If charging voltage and current increase to normal levels when ECM and regulator are bypassed, regulator is bad If system output remains the same with bypassed regulator, alternator is bad

Regulator Bypass Test (Cont.) (Ford)

12-Volt Charging System Scope Testing Connect red scope test lead to alternator battery (output) terminal Ground other scope lead Start engine and observe scope trace (waveform) Charging system should produce relatively smooth dc voltage trace with minimum ripple

12-Volt Charging System Voltmeter Test Charge battery, if drained before testing Set voltmeter to read low voltage Connect voltmeter test leads across battery terminals Measure and record battery base voltage Battery voltage with everything off

12-Volt Charging System Voltmeter Test (Cont.) Start engine and record no-load voltage Engine running and electrical accessories off Voltmeter reading should increase from base reading, but not by more than 2–3 volts Turn on all electrical accessories to load charging system Record load voltage

12-Volt Charging System Voltmeter Test (Cont.) Shows if charging system is providing current for all electrical units and still has enough current to recharge battery Calculate charge voltage using formula Load voltage – base voltage = charge voltage

VOM Test (Fluke)

12-Volt Circuit Resistance Tests Locate wiring problems in charging system Loose connections Corroded terminals Partially burned wires Perform resistance tests when symptoms point to problems other than alternator or regulator

Insulated-Circuit Resistance Test Connect tester across alternator output terminal and positive battery terminal With vehicle running at fast idle, turn load control to obtain 20 amp current flow All lights and accessories should be off

Insulated-Circuit Resistance Test (Cont.) If circuit is in good condition, voltmeter should not read over about 0.7 volts 0.1 volt per electrical connection If voltage reading is higher than 0.7 volts, circuit resistance is high and poor connection exists in that charging circuit section

Ground-Circuit Resistance Test Similar to insulated-circuit resistance test Voltmeter is placed across negative battery terminal and alternator housing Voltmeter should not read over 0.1 volt per electrical connection If voltmeter reads higher, look for Corroded or loose connections Burned plug socket Damaged wiring harness

Voltage Drop and Resistance Tests

Alternator Service Bad alternators show up in tests as low output or unclean dc problem Even with regulator bypassed and full voltage applied to alternator field, charging voltage and current will not meet specifications

Alternator Removal Disconnect battery to prevent major electrical short and wiring harness fire Loosen two bolts securing alternator to its mounting brackets Carefully pry alternator toward center of engine to loosen alternator belt

Alternator Removal (Cont.) Pull alternator belt off its drive pulley Disconnect wiring harness from rear of alternator Remove failed alternator (Mazda)

Alternator Disassembly Before disassembling alternator, scribe marks on outside of housing Follow shop manual directions when disassembling Use puller, if needed, to remove pulley May need Allen wrench to hold shaft

Alternator Disassembly (Cont.) Remove alternator through-bolts Tap drive end frame and end frame from rotor shaft with plastic or brass mallet Remove remaining alternator parts, and watch how everything fits together Keep all parts organized and clean If grease gets on brushes, replace them Grease or oil will ruin brushes

Alternator Disassembly (Cont.) (Fiat)

Alternator Rotor Service Bad alternator rotor can have bent shaft scored slip rings open windings, or shorted windings Short-to-ground test Measures resistance between rotor shaft and windings Should read infinite resistance to show no short to ground

Alternator Rotor Service (Cont.) Open circuit test Measures resistance between two slip rings Meter should read low resistance 2–4 ohms Rotor current test Checks windings for internal shorts Rotor current 3–6 amps

Alternator Stator Service Bad alternator stator can have shorted or open windings Inspect stator windings for signs of burning Use ohmmeter to detect open windings

Alternator Stator Testing

Alternator Diode Service Bad diodes reduce output current and voltage Diodes can be tested using Ohmmeter Test light Diode tester Scope Ohmmeter is most common testing tool used when alternator is disassembled

Ohmmeter Test of Diodes Connect meter to each diode in one direction then the other Meter should read High resistance in one direction Low resistance in the other Test each diode (Toyota)

Ohmmeter Test of Diodes (Cont.) Bad diode can either be shorted or opened Open diode Will have high (infinite) resistance in both directions Shorted diode Will have low (zero) resistance in both directions

Alternator Bearing Service Front alternator bearing or drive end bearing Cover plate and small screws hold it in place To replace bearing, remove screws and plate and lift out old bearing Rear alternator bearing, diode end bearing, or slip ring end bearing Normally pressed into rear end housing May be pressed or carefully driven out of alternator housing for replacement

Alternator Brush Service Worn brushes Affect alternator’s output voltage and current Inspect and measure their length When worn beyond specifications or soaked with oil or grease, replace them

Alternator Reassembly Install all components in rear end frame Electronic regulator Diode pack Rear bearing Terminals Nuts

Alternator Reassembly (Cont.) If brushes not mounted on outside rear of end frame, use piece of stiff wire or small Allen wrench to install brushes These will hold brushes back as rotor slides into housing Fit front end frame into position and check alignment pins or marks

Alternator Reassembly (Cont.) Install and tighten through-bolts Pull out wire or Allen wrench Brushes should click into place on slip rings Install any spacer, fan, front pulley, lock washer, and nut Torque pulley nut to specifications

Alternator Reassembly (Cont.) Spin rotor shaft and pulley Rotor should spin freely Test alternator output on bench tester Or test charging system output after alternator installation

Alternator Reassembly (Cont.) (Bosch)

Alternator Installation With battery still disconnected, fit alternator onto front of engine Install or reconnect wiring harness Hand start bracket bolts and screw them in without tightening Check alternator belt condition Replace if needed Slip belt over engine and alternator pulley, making sure it aligns properly on each pulley

Adjusting Alternator Belt Tension Pry on strong surface of alternator end frame Pull hard enough to produce minimum belt tension Alternator belt should wiggle up and down about an inch Overtightening an alternator belt is an expensive mistake Tighten adjusting bolt while holding pry bar

Adjusting Alternator Belt Tension (Cont.) Tighten any other mounting bolts Recheck belt tension by pulling up and down on belt with your fingers Reconnect 12-volt battery and rescan alternator voltage

Voltage Regulator Service Replace modern electronic regulator when it fails voltage test Electronic regulator locations On back of alternator Inside alternator On fender well Obtain correct replacement regulator Install it Recheck charging system output

Hybrid Charging System Service HV power control module (HV PCM) generates different voltage levels for various vehicle electrical systems 13–15 volts dc for conventional circuits 45 volts dc for heated windshield circuits High voltage for recharging HV battery Check dash instrumentation to verify proper operation

Hybrid Charging System Service (Toyota)

Scanning Hybrid Charging Systems Most common problems with HV charging system Bad HV PCM Bad motor-generator Failed hybrid control module Loose or corroded HV power cables

Measuring HV Battery Charging Voltage Drive vehicle in full-electric mode until HV battery drains and engine starts Connect HV multimeter to battery terminals or cable ends, where exposed Set meter to high voltage dc Raise and secure vehicle on jack stand or lift with drive tires off the ground

Measuring HV Battery Charging Voltage (Cont.) Start gas engine Have a helper press accelerator Spin front wheels at about 20 mph Hold pedal to stay in all-electric mode Read amount of dc voltage trying to recharge HV battery Voltage should be about 25% higher than HV battery itself

Measuring HV Charging Current Connect inductive ammeter to measure ac current flowing through HV power cables Place transmission shift lever in Park Block tires Install exhaust vent hose Engage ignition module and press Start button

Measuring HV Charging Current (Cont.) Press accelerator pedal until engine speed reaches about 2000 rpms System should detect drained HV battery and try to recharge it Read HV charging current in three orange HV power cables between HV PCM and motor-generator Same meter readings for each cable Within factory specifications

Scope Testing a Hybrid Charging System Wear high-voltage safety gear and use high-voltage appropriate tools Clip inductive pickup test lead over one of HV power cables between motor-generator and HV PCM Attach inductive or high-voltage test leads to each of 3-phase terminals on three orange power cables leaving motor-generator

Scope Testing a Hybrid Charging System (Cont.) Ground negative scope lead to vehicle’s metal frame Start engine to attempt to recharge HV battery Look at superimposed ac signals coming out of motor-generator to HV PCM Compare voltage, timing, and overall shapes to specifications

Scope Testing a Hybrid Charging System (Cont.) Shut off engine, but leave electrical accessories on Connect scope to 12-volt dc terminals on HV PCM Look at dc trace for 12 volts dc Must be perfectly straight, clean dc signal with no interference or rapid voltage fluctuations

Scope Testing a Hybrid Charging System (Cont.) Start gas engine and look at 12-volt dc waveform on scope screen Should form perfectly straight and smooth line on oscilloscope Compare the dc traces with engine off and engine running Any increase in dc signal abnormalities indicates ac interference entering dc circuitry

Measuring Motor-Generator Resistance Motor-generator resistance tests check continuity of conductors and windings in motor-generator If charging current in any ac cable is lower than others, disconnect cables and measure stator resistance of motor-generator Isolates problem to either motor-generator or HV PCM

Measuring Motor-Generator Resistance (Cont.) High ohmmeter reading across any stator connections Indicates one or more failed coil windings in stator Low ohmmeter reading Indicates one or more coil windings shorted to ground Requires motor-generator replacement

Measuring Motor-Generator Resistance (Cont.) If stator resistances within specifications Suspect HV PCM is not producing adequate charging current May have high internal resistance in orange power cables