How to Tell If Your Car Alternator Is Bad

A "clicking" noise when you start your car could be a bad alternator.

Most everyone has had the experience of going out in the morning to start the car, and just getting a “click.” “Click.” There are three problems that should come to mind when you hear the dreaded click. The starter or starter relay could be bad, the battery could be dead--or the alternator may have stopped working--in which case, the battery would be drained, causing the click.

Things You'll Need

• Voltmeter
• Jump box or jumper cables

Instructions

1. Set the voltmeter to read DC volts. Touch the positive lead to the positive battery terminal. Touch the negative lead to the negative battery terminal. If you read 12 volts or higher on the voltmeter, the voltage of the battery is correct. If the reading is higher than 14.5 volts, you have a situation where the battery is possibly being overcharged.

2. Attach the jump box to the battery by clamping the negative lead to the negative terminal and the positive lead to the positive terminal. Start the car. Read the voltage across the battery as directed in step 1; if the voltage is between 13.5 and 14.5, your alternator is good.

3. If the voltage is not between 13.5 and 14.5 and the voltage reads less than this, keep the voltmeter attached to the battery and monitor the reading. If the reading continues to drop, the alternator is not charging the battery. Replace the alternator.

Tips & Warnings

• Don't touch the jump box cables to each other. You could short out the jump box.

• Always hook the jump box to the negative side first, so you don’t inadvertently ground the jump box by touching the negative to metal while the positive is hooked to the battery.

• If the car starts, but the lights flicker or other electronics do not work or work intermittently, hook up the voltmeter as instructed in Step 1. Turn the lights and the radio on, or work the power windows. If the voltage drops significantly, replace the alternator.

• Always be careful when working with electrical systems. Watch where you lay wires and tools, so that you don’t inadvertently short out the battery or cause other damage to computers and other electronic components.