2. 33
Chapter
Charging System Diagnosis, Testing, and Repair

3. 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.

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

5. 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

6. 12-Volt Charging System Diagnosis (Cont.)
There are four common symptoms
Dead battery
Overcharged battery
Abnormal noises
Indicator shows problem

7. 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

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

9. 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

10. 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

11. 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. 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

13. 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

14. 12-Volt Charging System Tests
Charging system output test
Regulator bypass test
Scope testing
Circuit resistance tests

15. 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

16. 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

17. 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

18. 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

19. 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

20. Regulator Bypass Test (Cont.)
(Ford)

21. 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

22. 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

23. 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

24. 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

25. VOM Test
(Fluke)

26. 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

27. 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

28. 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

29. 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

30. Voltage Drop and Resistance Tests

31. 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

32. 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

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

34. 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

35. 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

36. Alternator Disassembly (Cont.)
(Fiat)

37. 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

38. 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

39. 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

40. Alternator Stator Testing

41. 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

42. 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)

43. 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

44. 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

45. 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

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

47. 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

48. 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

49. 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

50. Alternator Reassembly (Cont.)
(Bosch)

51. 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

52. 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

53. 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

54. 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

55. 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

56. Hybrid Charging System Service
(Toyota)

57. 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

58. 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

59. 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

60. 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

61. 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

62. 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

63. 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

64. 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

65. 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

66. 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

67. 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

68. 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