Car won't start: flat battery, starter motor or alternator?
How to tell the most common causes apart from what you hear and see when you try to start the car.
3 min read
A car that won’t start is frustrating, but what it does when you try to start it gives useful clues. Here’s how the three most common culprits usually show up, plus a few other causes worth ruling out.
A flat or failing battery
The battery is the most common cause. Signs include:
- the engine turns over slowly, or not at all
- a rapid clicking noise when you turn the key or press the start button
- dim or flickering dashboard lights, or lights that fade when you try to start
- the car has been sitting unused for a while, or something was left on overnight
Car batteries wear out with age. Many last somewhere around three to five years, and heat can shorten that. If your battery is getting on and starting has become sluggish, it’s worth having it tested before it lets you down.
A battery can also go flat if something is drawing power while the car is parked, or if the charging system isn’t doing its job (see the alternator below). If you’ve needed a jump start more than once, get the car checked rather than jump-starting it again.
The starter motor
The starter motor is what turns the engine over when you start the car. If it’s failing, you may notice:
- a single loud click, then nothing, while the dashboard lights stay bright
- a whirring or grinding noise without the engine turning over
- starting problems that come and go
The clue is that the electrics seem normal, with bright lights and a working radio, but the engine doesn’t turn over. That points away from the battery and towards the starter motor or its wiring.
The alternator
The alternator charges the battery while the engine is running. When it fails, the car often starts fine at first, but the battery isn’t being recharged as you drive. Signs include:
- the battery or charging warning light coming on while you’re driving
- headlights dimming, or electrical features acting strangely
- the car stopping while you’re driving, or being hard to start after a trip
- a new battery that keeps going flat
Because a failing alternator drains the battery, it’s often mistaken for a battery problem. Replacing the battery alone won’t fix it, which is why it’s worth testing the whole charging system, not just the battery.
Other common causes
Not every no-start is electrical.
- Fuel. An empty tank (fuel gauges can be wrong) or a fuel supply problem. If the engine turns over normally but won’t fire, fuel or ignition is a likely cause.
- Key or immobiliser. A flat battery in the key or a fault in the immobiliser can stop the car starting. A security light flashing on the dashboard can be a clue. If you have a spare key, try it.
- Gear selector. Most automatics won’t start unless they’re in Park (some also allow Neutral), and many cars need the brake or clutch pedal pressed to start.
What to do
- Don’t keep trying to start the engine for long periods. It can overheat the starter motor and flatten the battery further.
- If you know how to jump-start a car safely, follow the instructions in your owner’s manual. If you’re not sure, call roadside assistance instead. Connecting leads the wrong way can damage the car’s electronics or cause injury.
- If the car starts after a jump start, it still needs checking. The battery or the charging system may be on its way out.
If your car won’t start, or it’s getting harder to start, call Ridgeline Auto on 02 9000 0000 and we’ll help work out what’s going on.