How To Change A Faulty Alternator

When it comes to supplying power to a car’s music system, headlights, and other electronics, one might assume it is just the battery that’s important. In reality, it’s the alternator that helps keep things running! In this article, you will find basic steps on how to change a faulty alternator.

What does an alternator do?

An alternator is a very important part of a combustion engine vehicle. While the battery starts up the car, the alternator ensures that it continues to run smoothly. The alternator converts mechanical energy to electrical energy with an alternating current (AC). The alternating current is rectified into a direct current (DC) that charges the battery.

Aside from charging the battery, the alternator also powers all electronic components while you’re driving, including the headlights, power windows, windshield wipers, dashboard instruments and the car radio or entertainment system.

Alternators are likely to last the lifetime of a vehicle, however, since it is constantly exposed to heat damage, moisture and general wear and tear, they can fail and will need to be replaced.

What are signs of a failing alternator?

There are a number of signs that can indicate you have a failing alternator. Some of the most common symptoms of a failing alternator can also indicate a problem with the battery or starter motor. So it’s important to check if the battery is flat or dead when you experience similar symptoms. If the battery is flat then it’s likely to be an alternator issue.

Symptoms of a failing alternator include:

  • Slow or malfunctioning electrical accessories
  • Dimming or overly bright lights
  • Dead battery
  • Troubling starting up the car or frequent stalling
  • Burning smell from engine bay

close up of alternator

Can a faulty alternator drain the battery?

Rarely, a malfunctioning diode in the alternator’s rectifier can drain the battery of a car. Normally, diodes allow current to flow only in one direction, however, a faulty diode can keep the charging circuit open even when the engine is not running, resulting in a dead battery.

How to change a faulty alternator?

Changing an alternator takes roughly 2 hours and is generally achievable provided you have mechanic skills or training and experience with car repairs. If you’re not confident and do not have experience with car repairs, then it is highly recommended to get a qualified mechanic to replace a faulty alternator.

Depending on the make and model of your car, the alternator could be on top of or behind the engine, or buried further inside the engine bay. If it’s on top, it’s much easier to access and do the replacement, if not it’s much more challenging to remove the other components to reach the alternator. In this case, it’s almost always better to get a qualified mechanic to do the job.

Book An Alternator Replacement

Tools needed to change a faulty alternator:

  • A new alternator
  • Socket and ratchet set with extensions
  • Multimeter/ Voltmeter
  • Spanner set
  • Belt tensioner tool
  • Safety equipment
  • Memory saver (if needed)

Step-by-step on how to replace the alternator:

The procedure to replace an alternator will differ by manufacturer and it’s very important to follow the guidance provided in the manufacturer’s workshop manuals. Generally replacing the alternator could involve the following steps:

  1. Check if your car requires a memory save to back up any preset electronic data. Every vehicle is different – check your car’s user manual for more details.
  2. Take off the negative terminal on the battery and make sure it’s not getting grounded out.
  3. Locate the alternator – it’s usually mounted to the front of the engine. In some cases, it’s buried deeper inside the engine bay which may require a qualified technician as it would need a lot more specialist tools and knowledge of other engine components.
  4. At this point, you can choose to take photographs of the setup in case you want to refer back to it when removing and replacing any individual parts.
  5. If you find that the intake hose is blocking access to the alternator, then disconnect it along with the mass air flow sensor, by unscrewing the hose clamp.
  6. Use a belt tensioner tool to loosen the serpentine belt by pulling back the belt tensioner. When you’re done, you’ll have to reroute the belt around all the engine’s pulleys, so pay close attention to how it is connected to the other components. Some cars also have a handy diagram near the engine to show how the pulleys are connected.
    1. Look for the tensioner pulley which is a spring-loaded pulley. Using the tool, get to the end of the bolt and pull it towards you which will push the pulley towards the spring. You’ll notice that the serpentine belt is now loose which means you can take off the alternator.
  7. Inspect the alternator for bolts and any connecting wires. Disconnect the connectors and wiring starting with the battery cable. Be careful when working with electrical wiring as it can be dangerous. If you’re not qualified, it’s always safer to get a trained mechanic to do the alternator replacement job for you.
  8. Then proceed to remove the bolts to free up the alternator. You may have to use a breaker bar on older cars.
  9. Once you remove the alternator, use a metal brush or sandpaper to clean up the bracket it sits on as well as the bolts if you notice any corrosion. The better the connection between the bracket and the alternator, the better the alternator will perform.
  10. Place the old and new alternator side by side and compare to check where the mounting spots are located and that the alternator pulleys are the same size. Make sure it matches otherwise you will need to source a different correct alternator to proceed.
  11. Put the new alternator in the bracket and attach all wire connections using a torque wrench. This is optional but if you have anti-seize lubricant handy, you can apply this to the threads of the bolts which will make it easier if the alternator ever needs to be replaced in the future.
  12. Reinstall the belt, shifting the belt tensioner as required with the help of the belt tensioner tool. Inspect to check that the belt is on the pulleys and tensioned correctly according to manufacturer guidelines.
  13. If any other parts were removed to gain access to the alternator, make sure that everything is reinstalled as it should.
  14. Lastly, connect the negative terminal of the battery and you’re ready to test it with a voltmeter. Ensure the voltage is within the right range (13.5-14.5 volts) before you go for a test drive with the new alternator.

Disclaimer: this job involves work with electrical components. If you’re not familiar with electricals and are not a qualified mechanic, we recommend seeking professional help to change a faulty alternator.