Keep in mind that an undercharged battery is often caused by car accessories left on overnight, or by a rear compartment or dashboard compartment light that remains on.
When the charging system is operating normally, the charge indicator light comes on when the ignition switch is turned to ON and goes off when the engine starts. If the light does not come on with the key in the ON position, you will need to check the indicator light circuit or replace the bulb.
Alternatively, alternator noise can be caused by the following components:
Incorrect routing of hoses, wiring, or shielding against the alternator housing
A loose drive pulley
Loose mounting bolts
Worn or dirty bearings
A faulty diode
A faulty stator
Brush / slip ring friction
Precautions
Do not reverse the connections to the alternator.
Do not short-circuit or ground the charging circuit terminals, except as instructed.
Do not attempt to hot-wire the alternator by connecting B+ voltage to any of the terminals on the alternator’s 4-way connector. Use only an approved test harness as described in these instructions.
Never disconnect the output terminal while the alternator is running.
Use only approved terminal probe adapters to connect multimeter wires and jumper wires to the connector terminals. Using improper adapters will damage the terminals and result in failure of the charging system or test harness.
Inspection
Before testing the alternator, inspect the following components and conditions:
Battery: Check that the vehicle’s battery is in good condition and fully charged.
Battery built-in hydrometer: The green eye should be visible in the hydrometer.
Battery terminal voltage with all loads off should be greater than 12 volts.
Check that the battery connections are clean and tight.
Drive belt for damage or looseness.
Wiring harness to the alternator. Check that the harness connector is tight and locked. Check that the alternator output terminal is connected to the battery’s positive alternator wire.
All fuses and electrical connections related to the charging system for damage or looseness.
Diagnosis
If the battery tests well but still does not perform properly, the following causes are the most common:
A vehicle accessory was left on overnight
Driving speeds have been slow with frequent stops
The electrical load exceeded the generator’s output (especially with the addition of aftermarket equipment)
Existing conditions in the charging system include the following possibilities:
An electrical short circuit
A slipping belt
A faulty generator
A faulty generator voltage regulator
The battery has not been properly maintained, including in the following situations:
A failure to keep the terminals tight
A failure to keep the terminals clean
A loose battery hold-down device
A power failure caused by an existing mechanical condition in the electrical system, such as a shorted or pinched wire
Extended Vehicle Storage
Extended cranking periods due to a potential fuel or ignition system issue.
Incorrect interpretation of the battery’s built-in hydrometer
The ampere-hour charge rate is insufficient for a discharged battery
There is a continuous current draw on the battery through excessive parasitic drain
The battery is old
Self-discharge always occurs as a result of internal chemical reactions, even when the battery is not connected. In hot weather, this chemical reaction increases significantly. This is why the number of discharged batteries will increase in very hot weather.
Battery Capacity Test
To perform this test, use a high-rate discharge tester, Battery Tester, in conjunction with the digital multimeter 73.
Set the tester to the OFF position.
Turn the multimeter selector to the DV volt position.
Connect the tester and the multimeter’s positive test leads to the battery’s positive terminal and both negative test leads to the battery’s negative terminal. The multimeter clips must make contact with the battery terminals and not with the tester’s clips. Unless this is done, the actual voltage at the battery terminals will not be indicated.
Turn the load control knob clockwise until the ammeter reads approximately half of the battery’s cold cranking amps.
With the ammeter reading the required load for 15 seconds, note the multimeter reading.
If the multimeter reading is 9.6 volts at 21°C (70°F) or higher, the battery has good output capacity and readily accepts a charge, if needed.
If the voltage reading is below 9.6 volts at 21°C (70°F) and the battery is fully charged, the battery is damaged and a new battery must be installed. If you are unsure of the battery’s state of charge, charge it.
Once the battery is charged, repeat the battery capacity test.
If the battery capacity test voltage is still below 9.6 volts at 21°C (70°F), install a new battery.
If the voltage is 9.6 or higher at 21°C (70°F), the battery is satisfactory for service.
If the battery is only discharged, check for a loose drive belt, a loose electrical connection, charging system performance, and perform the battery drain test.
Caution: Avoid leaving the high-rate discharge load on the battery for periods longer than 15 seconds.
In-line Ammeter Drain Test
Check for current drains on the battery exceeding 50 milliamps with all electrical accessories off and the vehicle at rest. Current drains can be tested with the following procedure.
WARNING: Do not attempt to perform this test on a lead-acid battery that has recently been recharged. Explosive gases can cause injury.
To avoid damaging the meter, do not start the engine or use accessories that draw more than 10 A.
Note: Many computers draw 10 mA or more continuously. Use an in-line ammeter between the battery’s positive or negative terminal and its respective cable.
Position the switch to mA/A DC.
Disconnect the battery terminal and touch the probes.
Isolate the circuit causing the current leak by removing one fuse at a time from the fuse junction panel while reading the display. The current reading will drop when the fuse for the faulty circuit is pulled.
Reinstall the fuse and test the components (including connectors) of that circuit to find the faulty component(s). Test Conclusion The current reading (current drain) should be less than 0.05 ampere. If the current drain exceeds 0.05 ampere, a constant current drain is present. (Underhood, glove box, and trunk/ luggage compartment lamps that do not turn off properly are all possible sources of current drain.)
If the drain is not caused by a vehicle lamp, remove the fuses from the interior fuse junction panel one by one, until the cause of the drain is found.
If the drain is still not determined, remove the fuses one by one at the power distribution box to find the problematic circuit.
Alternator Test
To avoid damaging the alternator (GEN), do not perform any jumper connections except as instructed. Do not allow any metal object to come into contact with the housing and the internal diode cooling fins with the key on or off. A short circuit will result and burn out the diodes.
Note: Battery terminals and cable clamps must be clean and tight for accurate meter readings.
TURN OFF all lamps and electrical components.
Place the vehicle in the NEUTRAL transmission range and apply the parking brake.
Perform the load test and the no-load test.
Set the battery tester to the ammeter function.
Connect the battery tester’s positive and negative leads to the corresponding battery terminals.
Connect the current probe to the alternator B+ output wire.
With the engine running at 2000 rpm, the alternator output should be greater than that indicated on the chart.
Set the battery tester to the voltmeter function.
Connect the voltmeter’s positive lead to the alternator B+ terminal and the negative lead to ground.
Turn off all electrical accessories.
With the engine running at 2000 rpm, check the alternator output voltage. The voltage should be between 13.0 and 15.0 volts.