Car won't start: find the fault by the sound

What a no-start actually means

Starting a car depends on a short chain of parts, and each link fails in its own way. That is why noting exactly what happens narrows it down, even if a shop still has to test which part it is.

How a car starts

The battery delivers a large burst of current, and the starter motor uses it to spin the engine over. The engine then needs its air-fuel mixture, compression and spark to run on its own. Once it runs, the alternator takes over and recharges the battery for the next start.

Common causes

• A weak or worn battery. Most last three to five years.
• Corroded or loose battery terminals
• A failing starter motor
• A charging system fault that left the battery flat
• On a diesel in the cold: the glow plugs, or low compression
• On an electric car: the 12-volt battery, not the drive battery

What to do now

1. Listen to what happens when you try to start: a slow crank, a click, grinding, or a normal crank with no start.
2. Watch the headlights or dash lights as you try. If they dim sharply or go out, suspect the battery.
3. Look at the battery terminals for a white or bluish crust, and check that the clamps are tight.
4. On a diesel, wait for the glow plug symbol to go out before you crank.
5. If a jump-start gets you going, have the battery and charging system tested rather than relying on the next jump.

What do you hear?

• A slow crank: the battery, the starter or a connection.
• A click, but the engine does not crank: a weak battery, a failing starter or a bad connection.
• Headlights dim or go out as you try: the battery, its voltage sags under the starter's load.
• A grinding noise when starting: the starter or its engagement mechanism.
• Cranks normally but will not run: not the battery, look at fuel, spark or compression.
• Electric car will not wake or unlock: almost always the 12-volt battery.

What people often get wrong

That a car that won't start always has a dead battery. A click with no crank can also be a failing starter or a bad connection, and a battery that keeps going flat is often just the part that gave out first because something else was not charging it.

When the car must go to a workshop

If it happens again, or you need repeated jump-starts, have the battery and the charging system tested. On an electric car, ask for the 12-volt battery to be tested, not the drive battery.

Read next

• Glow plug light on a diesel: wait until it goes out
• Battery light on while driving: what it means
• The EV will not wake up: usually the small battery, not the big one

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.