Your car’s alternator is responsible for providing electrical power to the battery and auxiliary systems. If you ignore a malfunctioning alternator, it will eventually result in a dead battery or leave you stranded with a non-functioning vehicle on the roadside. Continue reading to discover the indicators of a faulty alternator and the basic steps involved in a do-it-yourself alternator replacement.

How to Determine if an Alternator is Faulty

It’s important to be aware of the established indicators of a malfunctioning alternator. While some charging system issues may involve wiring between the alternator and the battery, it’s generally wise to begin your diagnosis with the alternator since it’s responsible for supplying power to the vehicle’s electrical systems. Here are key signs to look out for:

  • Dead Battery: A working alternator is essential to keep your car battery charged. If your battery becomes depleted, it’s a good practice to test it . If the battery tests fine, there’s likely an issue with the alternator.
  • Dimming Lights: If you observe your headlights or other vehicle lights dimming or flickering, this may indicate insufficient current supply. Typically, the dimness will worsen as the alternator deteriorates.
  • Warning Light: Most vehicles feature a battery light, often mistaken for indicating a bad battery. In reality, it signals a problem with the alternator’s ability to charge the battery properly.
  • Sluggish Accessories: Another potential sign of alternator trouble is when electrical accessories or features like power windows operate more slowly than usual.

Being attentive to these warning signs can help you identify a faulty alternator and address the issue promptly.

Essential Tools for a Job Well Done

Before beginning the task, it’s crucial to collect all the required components and prepare for the work. Select a safe and level working environment. In addition to the replacement alternator, you will need the following tools:

  • Hand tools such as ratchets, sockets, and wrenches
  • Belt tensioner tool
  • Protective gloves and safety gear
  • Battery tender or memory saver (if necessary)
  • Jack, jack stands, and wheel chocks (if required)
  • Automotive designs can vary significantly from one vehicle to another, so you might require additional tools based on how your specific make and model was constructed. Not all cars will necessitate the last two items for the task, although some might. The requirements will vary depending on your vehicle’s design.




This step is of utmost importance to prevent any electrical shorts, and we strongly recommend you follow this procedure. Before you proceed with disconnecting the negative cable, it’s advisable to consult a vehicle repair manual to determine whether using a battery maintainer is necessary to avoid potential drivability and module re-programming issues.

Ensure that the ignition is in the ‘OFF’ position. Then, carefully detach the negative (ground) battery terminal, and make sure to cover it to prevent accidental contact during the task. You can easily identify the negative battery terminal as it is marked with a Minus sign (-).

This is also an opportune moment to clean, inspect, and test your battery. A weak or failing battery can lead to premature failure of the new alternator.


The alternator is affixed to the engine, typically on the front or side, depending on your vehicle’s make and model. If accessing the alternator from beneath the vehicle is necessary, you will require a hydraulic jack, jack stands, and wheel chocks to safely elevate the vehicle and create a secure working environment.


While checking the alternator, also assess these critical components in the starting and charging system:

  • Drive Belt: Examine for wear, cracks, or frays. Consider replacing it if needed, especially if it’s close to the recommended replacement mileage (around 90,000 miles).
  • Drive Belt Tensioner: If applicable, inspect the tensioner while removing the drive belt. It should move smoothly without sticking or binding. Ensure it’s not overly tight or loose.
  • Electrical Plug Pigtail Connector: Verify that the alternator pigtail and harness are clean and undamaged. Apply a bit of waterproof grease during installation if needed.
  • Battery Terminal B+ Voltage Wire: Check for damage or wear on the alternator’s 12v battery wire. If it shows signs of damage, replace it promptly.
  • Contamination on the Alternator: Look for any excessive oil, grease, or antifreeze on the alternator. Address the source of the contamination to prevent damage and warranty issues.


After inspecting and disconnecting the electrical connections, drive belt, and any interfering components, proceed to unbolt the old alternator from the engine and its mounting brackets.


Before installation, carefully compare the old alternator to the replacement unit. Pay close attention to the electrical connector plug-in position, design (shape), and the alignment of the alternator mounting bolt holes. Ensure that everything matches before proceeding with the installation.

NOTE: Manufacturers sometimes consolidate alternator designs, so don’t jump to conclusions if the replacement alternator appears different. Consult the installation documentation provided with the replacement unit to confirm that you have the correct alternator.


  • Align and loosely attach the alternator using its mounting bolts and nuts. Ensure even tightening of the fasteners. For some vehicles, connect the electrical components first due to accessibility.
  • Install the belt by initially placing it on grooved pulleys and then slipping it onto the smooth pulley. Be cautious not to force the belt onto the pulleys due to limited tensioner movement.
  • For vehicles with manual tensioners or those where the alternator controls belt tightness, maintain about ½ inch of belt deflection between pulleys with the greatest distance between them.


After reinstalling the alternator, drive belt, and electrical connections, ensure you’ve tidied the workspace and removed any loose items and tools. If you used a battery maintainer, follow the correct steps.

Clean and inspect the battery posts and cable connections. Replace as needed for secure connections.

Apply new felt washers on the clean battery posts and reattach the battery cable ends. Connect the positive cable first, followed by the negative (ground). Apply a coating of battery post grease on the cable ends and posts to prevent acid buildup and corrosion.

Next, test the alternator’s output. With the car running, you should see a voltage between 13.25 to 15 volts with a fully charged battery. If you only measure the battery’s standing voltage (around 12.2-12.5), your alternator isn’t charging correctly.

Remember: Ensure your battery is fully charged before starting. A low voltage battery can harm the new alternator.

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