Proper testing of an alternator requires the use of a multimeter or battery tester. An alternator produces direct current (DC) but can also produce alternative current (AC), which can damage the various electrical components of your vehicle, including the computer. Disconnecting the battery while the engine is running does allow you to identify if the alternator is weak, but poses potential harm to your engine. Use this method if no other alternative exists and practice extreme caution while doing so.
Things You'll Need
- Socket wrench
- Protective glasses
- Rubber gloves
Start the vehicle and engage the emergency brake.
Open the hood and locate the battery. Stand to the side of the battery while disconnecting it to avoid the moving parts of the engine (fan and belts).
Turn off all unnecessary components, such as the lights, radio, and A/C, to limit the drain on your alternator. Allow the vehicle to warm up to operating temperature.
Put on protective glasses and rubber gloves. Disconnect the negative lead from the battery and set it to the side.
Run the engine uninterrupted for 15 to 30 minutes. Do not rev the engine or drive, if possible. A healthy alternator will allow the vehicle to run.Reconnect the negative lead to the battery if no interruptions or issues are noted.
Check all the fuses and reconnect the battery if there is an interruption in the vehicle running. If all of the fuses are fine, take your vehicle to an auto shop to have your alternator professionally tested. You likely have a bad alternator.
Tips & Warnings
- Doing this repeatedly could cause a good alternator to go bad as you are placing a greater strain on the alternator.
- Photo Credit Hemera Technologies/AbleStock.com/Getty Images
Car AC Pressure Switch Testing
Auto air conditioning pressure switch testing allows you to diagnose potential or existing AC problems. Pressure testing the vehicle's low and high...
How to Check if Your Alternator is Charging Your Battery
When diagnosing battery trouble, you must check the alternator to see if it is charging correctly. If the alternator is not working...
How to Test Your Car Alternator for Power
When a car battery isn't providing enough power to start a car, people often assume that the battery is bad. Before buying...
How to Test If Your Car Battery or the Alternator Is Bad?
Testing the alternator or battery in your car requires a digital multi-meter with a voltage setting on it. The battery in your...
How to Disconnect a Battery While a Car Is Running
Some people believe disconnecting a car's battery with the engine running is an easy way to tell if the car's alternator is...
How to Test an Alternator With a Meter
Testing your alternator with a voltmeter is the easiest and most effective way to find out if it has enough power to...
How to Test the Alternator With the Battery
If your car is routinely suffering from a dead battery, you may begin to wonder if the problem is the battery itself...
Disconnecting the Battery from the Alternator
Having battery or alternator problems? Learn how to disconnect a battery from the alternator with expert tips in this free car repair...
How to Test a Car Battery
Testing a car battery is done prior to checking the alternator. Learn how to check a car battery before replacing or rebuilding...