How an engine’s alternator works

Alternator Replacement Image

A car’s alternator is responsible for generating power for various systems (headlights, radio, heater motor, heated rear window etc) as well as recharging the battery, and without it your car won’t run for long.

The alternator is driven by the serpentine belt (sometimes it gets its own alternator belt), which is powered by the engine’s crankshaft. It turns mechanical energy into electrical energy in the form of an AC current, which has to be turned into DC current via diodes for use in the car’s electrical systems.

This task requires experience. A basic toolkit should suffice though, and the job should take less than two hours, depending on your model.

Every car is different, so before you view the full instructions, find yours…

When to change your alternator

“Your headlights will dim, other car electrics will start to malfunction and you’ll have to jump-start your car to get it started”

An alternator’s bearings cause most failures (it starts to get noisy when the engine is running), but the drive belt can snap or become loose.

When the alternator isn’t working your battery isn’t being charged (you should see a red warning light or other message on your dashboard) and it’ll go flat quickly - your headlights will dim, other car electrics will start to malfunction and you’ll have to jump-start your car to get it started. But this won’t work for long before the battery fails completely.

If the alternator glitch has been caused by drivebelt failure, you should be able to get away with tightening or replacing the belt, but if the alternator is faulty it should be replaced without delay.

All cars are slightly different, so if it is time to change your alternator, use our before you begin checklist, and find your car for specific instructions.

How to change your alternator

This is a clip from a sample video. Find the full step-by-step task for your model

A very brief summary of the task:

  1. Disconnect the negative lead from the battery
  2. Depending on your model, you may need to remove other engine parts to gain access to the alternator. Haynes will tell you how to do this
  3. Disconnect the alternator’s electrical connections and mounting bolts. Remove it
  4. Make sure the new alternator matches the old one and has a pulley fitted. Install it and replace any components removed earlier

Why you should change your alternator

Alternator Image

An alternator is crucial to a car’s operation, especially in a modern car where electronics such as processors govern so many systems. Without the electricity generated by the alternator, the car won’t run for long.

The alternator keeps the battery charged. This is important not only for starting the engine but also for running power-heavy systems when the car is running, such as heated seats, heated screens, ventilation motors etc.

Before you begin

Tools you will need

Mainly basic tools are required for this job, although you’ll need a torque wrench and you may need to raise the car to remove the undershield/inner fender splashield.

  • Floor jack (not your car’s emergency jack)
  • Axle stands
  • Ratchet and socket set
  • Torque wrench
  • Flat-bladed/Phillips/torx screwdriver

Every car is different, so before you view the full instructions, find yours…