‘Why won’t my car start?’ – The 7 most common reasons for engine failure

Car engines are complicated pieces of engineering, so there could be a whole host of issues responsible for preventing your car from starting when you put the key in the ignition.

But some engine problems occur more frequently than others, so let’s take a look at the 7 most common causes of engine failure, and find out why your engine isn’t turning over.

1. Fuel pump failure

Fuel pumps are responsible for supplying the injectors with pressurised fuel which aids combustion, but their failure is one of the most common reasons for a non-starting engine.

Fuel pump failure can occur at any time, but running a car on less than ¼ of a tank of petrol for extended periods – or running out of fuel entirely – can cause premature damage.

2. Clogged fuel filter

Fuel filters can clog, so they should be replaced every 12,000 miles or so.

If you have a clogged or dirty fuel filter, the fuel may not be able to reach the engine, which prevents the engine from starting.

3. A problem with the timing belt

The timing belt (or cam belt) is the toothed rubber belt that connects the crankshaft to the camshaft. It controls the engine timing and makes sure that the valves and pistons don’t collide when the engine is in motion.

Over time, timing belts are prone to wear and can fail, causing the engine to operate out of sync. Owner’s manuals might disagree about how often a timing belt needs to be changed, but you should really check and replace one after covering somewhere in the region of 60,000 to 100,000 miles.

4. The battery’s dead

Car batteries are like any other kind of battery: they don’t last forever. They can fail and be drained of power if the cars lights or radio are left on while the car isn’t running, or if the car hasn’t been used for a while.

5. …or it’s corroded

Battery corrosion typically occurs when there are loose connections on the battery terminals, or when gases from inside the battery escape (whether though faulty or cracked battery caps or punctures in the battery itself).

Electrical resistance develops as the corrosion builds up, but by removing the negative and then positive terminals from the battery, the corrosion can be scrubbed away with a stiff brush.

6. Electrical problems

Even small fluctuations in voltage can cause damage to the engine’s computerised controls, and poor electrical connections could also be responsible for an engine failing to start, so they should be checked to make sure they’re not loose.

7. Distributor cap

Since the distributor cap carries voltage it can become worn, clogged and dirty, and prevent the engine from turning over.

Check your distributor cap for cracks, signs of fire damage or a build-up of dirt. It may need cleaning or replacing entirely.