Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Electrical Specified Value Inspection (Using the Voltmeter and Ammeter)
- Voltage Drop Test of Alternator Output Wire This test determines whether or not the wiring between the alternator "B" terminal and the battery (+) terminal is good by the voltage drop method.
- Preparation
- Turn the ignition switch to "OFF".
- Disconnect the output wire from the alternator "B" terminal. Connect the (+) lead wire of ammeter to the "B" terminal of alternator and the (-) lead wire of ammeter to the output wire. Connect the (+) lead wire of voltmeter to the "B" terminal of alternator and the (-) lead wire of voltmeter to the (+) terminal of battery.
- Test
- Start the engine.
- Turn on the headlamps and blower motor, adjust the engine speed until the ammeter indicates 20A and read the voltmeter.
- Result
- The voltmeter may indicate the standard value.
Standard value: 0.2V max
- If the value of the voltmeter is higher than expected (above 0.2V max.), poor wiring is suspected. In this case check the wiring from the alternator "B" terminal to the battery (+) terminal. Check for loose connections, color change due to an over-heated harness, etc. Correct them before testing again.
- Upon completion of the test, set the engine speed at idle. Turn off the headlamps, blower motor and the ignition switch.
- The voltmeter may indicate the standard value.
- Preparation
- Output Current Test
This test determines whether or not the alternator gives an output current that is equivalent to the normal output.
- Preparation
- Prior to the test, check the following items and correct as necessary.
Check the battery installed in the vehicle to ensure that it is in good condition. Refer to the "BATTERY " information for checking battery.
The battery used to test the output current should be partially discharged.
With a fully charged battery, the test may not be conducted correctly due to an insufficient load.
Check the tension of the alternator drive belt. Refer to INSPECTION the "Inspect drive belt" information for checking the belt tension.
- Turn off the ignition switch.
- Disconnect the battery ground cable.
- Disconnect the alternator output wire from the alternator "B" terminal.
- Connect a DC ammeter (0 to 90A) in series between the "B" terminal and the disconnected output wire. Be sure to connect the (-) lead wire of the ammeter to the disconnected output wire.NOTE:
- Tighten each connection securely, as a heavy current will flow. Do not rely on clips.
- Connect a voltmeter (0 to 20V) between the "B" terminal and ground. Connect the (+) lead wire to the alternator "B" terminal and (-) lead wire to a good ground.
- Connect the battery ground cable.
- Leave the engine hood open.
- Prior to the test, check the following items and correct as necessary.
- Test
- Check to see that the voltmeter reads the same value as the battery voltage. If the voltmeter reads 0V, open circuit in the wire between alternator "B" terminal and battery (+) terminal or poor grounding is suspected.
- Start the engine and turn on the headlamps.
- Set the headlamps to high beam and the heater blower switch to HIGH, quickly increase the engine speed to 2, 500 RPM and read the maximum output current value indicated by the ammeter.
NOTE:- After the engine start up, the charging current quickly drops. Therefore, the above operation must be done quickly to read the maximum current value correctly.
- Result
- The ammeter reading must be higher than the limit value. If it is lower despite the alternator output wire is in good condition, remove the alternator from the vehicle and test it.
Limit value: 60% of the voltage rate
Information
- The nominal output current value is shown on the nameplate affixed to the alternator body.
NOTE:- The output current value changes with the electrical load and the temperature of the alternator itself. Therefore, the nominal output current may not be obtained. If such is the case, keep the headlamps on to discharge the battery or use lights of other vehicles to increase the electrical load.
The nominal output current may not be obtained if the temperature of the alternator itself or ambient temperature is too high. In such a case, reduce the temperature before testing again. - Upon completion of the output current test, lower the engine speed to idle and turn off the ignition switch.
- Disconnect the battery negative (-) terminal.
- Remove the ammeter and voltmeter and the engine tachometer.
- Connect the alternator output wire to the alternator "B" terminal.
- Connect the battery negative (-) terminal.
- The ammeter reading must be higher than the limit value. If it is lower despite the alternator output wire is in good condition, remove the alternator from the vehicle and test it.
- Preparation
- Regulated Voltage Test
The purpose of this test is to check that the electronic voltage regulator controls voltage correctly.
- Preparation
- Prior to the test, check the following items and correct if necessary. Check that the battery installed on the vehicle is fully charged. Refer to the "BATTERY " information for checking the battery.
Check the alternator drive belt tension. Refer to INSPECTION the "Inspect drive belt" information for checking the belt tension.
- Turn ignition switch to "OFF".
- Disconnect the battery negative (-) terminal.
- Connect a digital voltmeter between the "B" terminal of the alternator and ground. Connect the (+) lead of the voltmeter to the "B" terminal of the alternator. Connect the (-) lead to good ground or the battery (-) terminal.
- Disconnect the alternator output wire from the alternator "B" terminal.
- Connect a DC ammeter (0 to 90A) in series between the "B" terminal and the disconnected output wire. Connect the (-) leadwire of the ammeter to the disconnected output wire.
- Connect the battery negative (-) terminal.
- Prior to the test, check the following items and correct if necessary. Check that the battery installed on the vehicle is fully charged. Refer to the "BATTERY " information for checking the battery.
- Test
- Turn on the ignition switch and check to see that the voltmeter indicates the following value.
Voltage: Battery voltage
If it reads 0V, there is an open circuit in the wire between the alternator "B" terminal and the battery and the battery (-) terminal.
- Start the engine. Keep all lights and accessories off.
- Run the engine at a speed of about 2, 500 RPM and read the voltmeter when the alternator output current drops to 10A or less
- Turn on the ignition switch and check to see that the voltmeter indicates the following value.
- Result
- If the voltmeter reading doesn't agree with the standard value, the voltage regulator or the alternator is faulty.
Regulated Voltage: 11.7 - 15.3V
- If the voltmeter reading doesn't agree with the standard value, the voltage regulator or the alternator is faulty.
- Disconnect the battery negative (-) terminal.
- Remove the voltmeter and ammeter.
- Connect the alternator output wire to the alternator "B" terminal.
- Connect the battery negative (-) terminal.
- If the voltmeter reading doesn't agree with the standard value, the voltage regulator or the alternator is faulty.
- Preparation
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.