Chapter 33

Modern
Automotive
Technology

Presentations for PowerPoint

CHAPTER 33
12-Volt and HV
Charging System
Diagnosis, Testing,
and Repair

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Objectives

• Inspect a 12-volt and high-voltage (HV) charging system to locate

obvious troubles.

• Diagnose 12-volt charging system problems.
• Test 12-volt charging systems.
• Remove and reinstall an alternator.
• Diagnose high-voltage hybrid charging system problems.
• Correctly answer ASE certification test questions on charging system

service.

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12-Volt Charging System Diagnosis

• 12-volt charging system has only two major parts:

• Alternator
• Regulator

• Troubleshooting can be difficult

• Another system’s fault may appear to be caused by charging system

problems

• Bad starting motor, defective battery, computer failure, or faulty wiring

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12-Volt Charging System Problems

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Common Symptoms

• Four common symptoms of charging system problems:

• Dead battery
• Overcharged battery
• Abnormal noises
• Dash indicator light or symbol glowing

• Verify these problems by trying to start engine

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Warning: Heated Windshield
Safety

• Some late-model cars are equipped with heated windshield
• When windshield is being heated, the alternator produces 110 volts

ac

• Enough voltage to cause electrocution
• Keep this in mind when working on this type of system

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Preliminary Inspection (1 of 2)

• Visually inspect charging system parts
• Check for battery-related problems
• Make sure belt tension is adjusted to specifications
• Check condition of alternator drive belt
• Check for loose or corroded electrical connections, shorted wires,

and other wiring problems

• Particularly connections on back of alternator

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Preliminary Inspection (2 of 2)

• Wiggle wiring harness from alternator to firewall or ECM while

engine is running

• If indicator light goes out or indicator gauge begins to read when wire

is moved, problem is in that area of wiring harness

• With engine running, listen closely for abnormal noises in alternator

• Internal grinding, whining, or other unusual sounds
• If necessary, use stethoscope

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Scanning 12-Volt Charging Systems

• Connect scan tool or diagnostic laptop to aid in troubleshooting
• Scan tool will display

• Charging voltage
• Battery temperature
• Other useful data

• Capabilities vary with each model

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12-Volt Charging System Precautions

• Disconnect battery before removing any charging system

component

• Never reverse polarity

• Battery or jumper cables connected backward can lead to serious

damage

• Do not operate alternator with output wire disconnected
• Never short or ground any charging system terminal

• Unless instructed to do so by service information

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12-Volt Charging System Tests

• Scan tool test
• Load test
• Scope tests
• Voltmeter test
• Circuit resistance tests

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Scan Tool Test

• Access alternator charging voltage with scan tool or diagnostic tablet
• Start and idle engine
• Turn on all electrical accessories to load alternator
• Use scan tool to access datastream values
• Scroll to alternator or charging system live voltage readings

• Alternator output of at least 13 volts indicates normal operation
• Below 12.6 volts means charging system is not producing enough current

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Tech Tip: Scope Function

• Most laptops and diagnostic tablets have scope function
• Scope function converts datastream voltage readings into live

scope waveforms for advanced troubleshooting

• Smooth dc is required for proper operation of ECMs and their

sensor circuits

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Charging System Load Test (1 of 2)

• Connect tester leads

• Procedures differ with each tester

design

• Set load tester controls to proper

positions and values

• Attach vent hose to exhaust and

start engine

©Snap-on Incorporated

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Charging System Load Test (2 of 2)

• Set load control on tester until alternator’s rated amperage is

displayed

• Do not exceed alternator’s output rating in amps
• Do not let voltage drop below full battery voltage

• Note alternator output current at 12.6 volts
• Turn off load control and evaluate readings
• If alternator output current is low, suspect bad alternator/regulator

assembly

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Scope Test

• 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

• Abnormal voltage ripple indicates bad alternator diodes

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Voltmeter Test (1 of 3)

• Charge battery, if drained before testing
• Set voltmeter to read low voltage
• Connect voltmeter test leads across

battery terminals

Fluke

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Voltmeter Test (2 of 3)

• Measure and record

• Base voltage
• No-load voltage
• Load voltage

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Voltmeter Test (3 of 3)

• Calculate charge voltage

• Load voltage – base voltage = charge voltage

• Charge voltage should be at least 0.5 volts with engine at warm idle
• Load voltage must be higher than base voltage for battery charging
• No-load voltage must be within specifications

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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

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Insulated-Circuit Resistance Test

• Connect voltmeter across alternator output terminal and positive

battery terminal

• With vehicle running at fast idle, turn on all lights and accessories
• Voltmeter should not read over about 0.7 volts

• If voltage reading is higher, circuit resistance is high
• Poor connection exists in that charging circuit section

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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 volts per electrical connection
• If voltmeter reads higher, look for:

• Corroded or loose connections
• Burned plug socket
• Damaged wiring harness

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Connections for an Insulated-Circuit
Resistance Test

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Connections for a Ground-Circuit
Resistance Test

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Alternator Service

• Bad alternators show up in tests as low output or unclean dc

problems

• Most shops replace alternators that exhibit these symptoms

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Alternator Removal (1 of 2)

• Disconnect battery’s negative cable

• Prevents major electrical short and

wiring harness fire

• Remove alternator belt off its drive

pulley

• Disconnect wiring harness from rear

of alternator

• Remove bolts that secure alternator

Mazda

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Alternator Removal (2 of 2)

• Alternator may come out from top, side, or bottom of engine

compartment

• If removed from bottom, splash shield may need to be removed
• If removed from side, inner fender apron may need to be removed

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Alternator Installation (1 of 2)

• Make sure battery is disconnected
• Ensure that new and old alternators match
• Fit and hold alternator onto engine with mounting bolt holes aligned
• Start alternator mounting bolts by hand, then tighten
• Reconnect wiring harness
• Check alternator belt condition; replace if needed

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Alternator Installation (2 of 2)

• Check condition of all idler pulleys

• Spin them to check for dry, rough, or loose bearings

• Slip and work belt over all of its pulleys
• Make sure belt is aligned properly on each pulley

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Hybrid Charging System Service

• HV PCM generates different voltage levels for various vehicle

electrical systems

• 13–15 volts dc for conventional circuits
• 45–110 volts dc for heated windshield circuits
• High voltage for recharging HV battery

• Check dash instrumentation to verify proper operation

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Scanning Hybrid Charging Systems

• Scanning will indicate most problems in HV

charging system

• Diagnostic codes will indicate problems with

all major components and circuits affecting
charging voltage

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Dash Instrumentation

• Check dash instrumentation to verify proper charging system

operation

Toyota

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HV Charging System Problems (1 of 2)

• HV PCM

• Converter and inverter circuits, contactors, transformers, diodes, and

power transistors

• Motor-generator

• Failure to output normal 3-phase voltage

• Hybrid control module

• Problem with control module itself or its connecting circuits

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HV Charging System Problems (2 of 2)

• HV power cables

• Faulty, loose, or corroded
• Bad HV cable connections

• HV battery

• Failure to take or hold proper electrical charge

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Test-Driving a Hybrid Vehicle in Electric
Mode

• It is best to drive up small hill

• Increases load on motor-generator
• Draws more current from HV battery

• Compare electric drive and charging circuit performance to that of

known good vehicle and system

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Tech Tip: Training for Hybrid
Charging System Diagnosis and
Repair

• Hybrid vehicle designs, operation, and repair procedures vary
• Become properly trained to diagnose and repair hybrid charging

system

• Attend manufacturer’s training courses
• Read manufacturer instructions on specific make and model