Car Won't Start? What to Check First, and What It Costs

It is 7:43 on a Monday. You press the start button and hear rapid clicking from under the bonnet, and nothing else. The battery read 12.4 volts last weekend, so this is not supposed to be happening. Before you call a tow, that exact sound has already narrowed the problem down to two parts.

Is it safe to keep turning the key?

Yes, in short bursts, with two exceptions. Stop straight away if you smell petrol or diesel around the car, and stop if the engine makes a loud metallic bang while it is turning over. Otherwise crank for no more than ten seconds at a time and wait about thirty seconds between attempts. Longer than that overheats the starter and drains what charge is left in the battery.

If the car is on a live road or a slip road, that is the real risk here, not the engine. Get the hazard lights on and, if you can, get the car and yourself off the carriageway before you start diagnosing anything.

What is your car doing when you turn the key?

This is the question that splits the diagnosis, and you have already answered it without any tools.

• Nothing at all. No sound, no dash lights, no interior lights. That is a completely flat battery, a disconnected battery cable, or a blown main fuse.
• Rapid clicking. The starter's engaging switch is chattering because the battery has some charge but not enough to turn the engine. This is the most common no-start of all, and it is almost always the battery.
• One loud click, then silence. The switch fires but the starter motor does not turn. Usually a failed starter, though a very flat battery can do the same. A jump start separates the two.
• The engine turns over but never fires. The starter and battery are fine. The engine is missing fuel or spark.
• It starts for a second or two, then dies. Usually fuel pressure that cannot be sustained, or a key the car does not recognise.

What does it cost to fix?

The figures below are rough forecasts, not quotes. Labour is what moves them most, because the same part can be a half hour job on one car and half a day on another.

Two things move the number. Where the starter sits on your engine decides whether it is a 30 minute job or three hours of labour, and a battery replaced at a parts shop costs far less than the same battery fitted at a dealer.

What should you do right now?

1. Open the bonnet and look at the two battery terminals. White, green or blue crusty buildup is stopping current getting through. Clean it off with a wire brush, or with baking soda and water, then retighten both clamps. This costs nothing and fixes a surprising share of no-starts.
2. Read the stored fault codes. The car keeps them even when the engine will not run, and any 15 to 30 euro ELM327 Bluetooth adapter plugs in under the dash so an app on your phone reads them in about a minute. A stored code often names the exact part that has failed.
3. Try a jump start. If the car fires immediately on jump power, the battery is the answer, and the only question left is whether it needs charging or replacing. If it still gives one click, look at the starter.
4. Book a workshop or call recovery if the first three come back clean. Tell them what you heard when you turned the key, whether a jump changed anything, and any code you read.

How do you check if the battery is the problem?

The battery causes more no-starts than everything else put together, so rule it out before you spend a euro anywhere else.

Look at it. Crusty buildup on the terminal posts is resistance, and resistance is exactly what stops a starter turning. Clean and retighten. That alone is the fix more often than most people expect. Use the headlights as a test. Turn them on without trying to start. Bright lights that dim heavily when you turn the key mean the battery has charge but cannot deliver the current the starter wants. Lights that are already dim, or will not come on, mean it is flat. Jump it. A car that fires instantly on jump power has a battery problem, full stop. A battery that goes flat overnight in mild weather needs replacing. One that went flat because the lights were left on may just need a proper charge. Check its age. Most car batteries last three to five years. Past four, it is the prime suspect whatever else you find. Capacity fades slowly and then fails all at once, usually on the first cold morning of the year, which is why a seasonal check before winter is worth the half hour.

Once the car is running again, scan it. A struggling battery makes the engine computer log odd codes as the power dipped during cranking, and those are worth clearing so they do not confuse the next diagnosis. Our OBD2 live data guide explains what the app is showing you.

That scan is the step most people skip, because a car that will not start feels like something only a workshop can look at. Skanyx reads the stored codes as long as the ignition powers up, even when the engine will not run: a crank sensor code or a fuel pump circuit fault each point at a different fix, and it shows the battery voltage beside them. That is how you tell a free terminal clean from a 200 to 650 euro starter or pump, and whether to call for a tow. Read the codes with the key turned to ignition

Car won't start but the battery is good

This is the second most searched version of the problem, and it has a short list of answers.

The starter motor. If a jump start does not help, the headlights stay bright, and you get one click or nothing, the starter is next. There is a crude test that genuinely works: have someone turn the key while you tap the starter body firmly with a spanner. If it fires, the brushes inside are worn and making poor contact. It will fail again, but the tap can get you home. Replacement runs 200 to 600 euros, mostly depending on how buried it is. A cable that tests fine and fails under load. The starter has a thick cable from the battery and a thin one from the ignition switch. A loose or corroded thick cable behaves exactly like a dead starter, because a battery can read a perfect 12.6 volts at rest and still deliver nothing through a bad joint. Check both ends are clean and tight before you buy anything. The fuel pump. Turn the key to on without starting and listen at the back of the car for a two second hum. That is the pump priming. Silence there means the pump, its fuse or its relay. A blown fuse is a free diagnosis and worth checking first. A key the car does not recognise. Modern cars will not fuel or spark until the key is accepted. A security light flashing on the dash after you turn the key is the tell. If you recently had a key cut, it may never have been programmed. Try your spare.

Why does the engine crank but not start?

The engine turns at normal speed and refuses to fire, so the starter and battery are both fine. An engine needs fuel, spark and compression. Compression failures are rare and happen slowly, so start with the first two.

Fuel. The two second hum test above tells you whether the pump is running. If it is silent, check the pump fuse and relay in the fuse box. With a working fuse and no pressure at the fuel rail, the pump has failed. Spark. Take one spark plug out, reconnect it to its lead or coil, hold it against bare metal on the engine, and have someone crank. You should see a spark jump the gap. No spark means an ignition fault: a failed coil, a failed ignition module, or the sensor that tells the engine where it is in its rotation.

That last one is the single most common part failure behind a cranks-but-no-start. Without its signal the engine computer does not know when to fire, so it does not fire at all. Replacement is 50 to 180 euros.

The codes. A scan here earns its keep, because the stored code usually names the part. The common ones are crank position faults such as P0335, cam position faults such as P0340, and fuel pump circuit faults. Key recognition problems sit on a separate system and show up on their own.

Why does the engine start and immediately die?

It catches, runs for one to three seconds, and stalls. That specific pattern has a short list.

The key is being rejected. The engine runs on the fuel already in the rail, then the car cuts the injection. A flashing security light gives it away. Try the spare key. The idle cannot be held. The engine starts but cannot keep itself running without your foot on the pedal. On older cars the idle air valve sticks shut. On newer ones the air flap needs cleaning or relearning. Fuel pressure collapses. The pump primes and delivers enough to catch, then cannot sustain it. A leaking regulator, a leaking sprayer or a dying pump all do this. A large air leak. A big disconnected hose or a torn intake boot leans the mixture out so badly that the engine cannot idle. It may run if you hold the throttle slightly open.

Why does my car only sometimes fail to start?

Intermittent no-starts are the hardest, because the fault is usually absent when the mechanic looks.

Keep a log. Write down the conditions each time: hot or cold engine, weather, how long the car sat, and whether it cranked or clicked. Patterns appear quickly. Failing only when hot suggests a heat sensitive part. Failing only when cold suggests the battery or the cold start settings. Many common car problems share this pattern and are traceable through the snapshot the car stores with each code. Suspect connections before parts. Intermittent faults are far more often a corroded or loose joint than a failed component. Battery terminals and starter wiring first, then earth straps and fuse box connections, especially on cars over eight years old. Get the battery load tested. A battery can read a healthy 12.6 volts and still collapse the moment the starter pulls on it. Most parts shops do a load test free and will tell you if it is on its way out.

Can you fix it yourself, or is this a workshop job?

You can do this at home if the answer is at the cheap end. Cleaning terminals, checking and swapping fuses, jump starting, listening for the fuel pump prime and trying the spare key need no tools beyond a wire brush and a torch. Replacing a battery is a fifteen minute job on most cars.

Call a workshop or recovery when the engine bangs loudly while cranking, when you can smell fuel, when the engine turns over very slowly despite a known good battery, or when you see smoke or steam. Those are stop-now signs, and continuing to crank makes each of them worse. A buried starter, a fuel pump inside the tank and key programming are all workshop or dealer jobs.

A fair visit looks like this. The diagnostic charge is typically 30 to 80 euros at an independent shop, and reading a code is a two minute job that no one should bill an hour for. The quote should list parts and labour separately and say what was actually measured. If a shop proposes a new starter without having jumped the car first, ask them to.

It is still 7:43 and the car is still on the drive, but the clicking has already told you where to look. Ten minutes with a wire brush and a code read separates a free fix from a tow, and it costs nothing to find out which one you have. Start at the battery terminals, because that is where this ends more often than anywhere else.

Codes named in this guide: P0335, P0340.