There are few sounds more frustrating to a driver than the engine turning over and over, but never actually catching and firing into life. You turn the key, you hear that familiar 'whirr-whirr-whirr' sound – which we call cranking – but the engine just refuses to start. It feels so close, yet so far! This is a very common problem, and the good news is that the cranking sound itself tells us a lot. It means your battery has enough power to turn the starter motor, and the starter motor is doing its job of turning the engine's crankshaft. This is a great starting point for diagnosis. It tells us the problem isn't a simple flat battery, but lies somewhere else. The issue is that one of the three essential ingredients for combustion – fuel, spark, or air (specifically, compression) – is missing. Your engine is turning, but it's not getting what it needs to ignite and run on its own. In this guide, we'll walk through what's happening, what the most likely culprits are on UK cars, and what to expect when you get it to a garage.
What this usually means
When a mechanic hears 'it cranks but won't start', we immediately think of the 'fire triangle': fuel, spark, and compression. For an engine to run, it needs all three at the right time. The fact your engine is cranking tells us the electrical system is at least partly working (battery, starter motor), but the final step – combustion – is failing. Here’s a simple breakdown of what’s missing: * **No Fuel:** The engine is getting a spark, but there's no petrol or diesel being injected into the cylinders. This is the most common reason for a non-start condition after a flat battery. It could be fo
Most common causes (UK cars)
In my 30 years on the tools, a 'crank, no start' job nearly always comes down to one of these usual suspects. We see them day in, day out in UK workshops. * **Fuel Pump Failure:** This is a big one. The electric fuel pump sits inside your fuel tank and pushes petrol or diesel up to the engine. They can fail without warning. You might be able to hear a faint hum from the back of the car for a couple of seconds when you turn the ignition on – if that sound is absent, the pump is a prime suspect. Fuses or relays that power the pump can also fail. * **Crankshaft Position Sensor (CPS) Failure:** Th
What to check yourself before booking in
Before you call for recovery, there are a few simple and safe things you can check that might just solve the problem or at least give a mechanic valuable information. Don't go pulling bits off the engine, just stick to these basics. 1. **Check the Dashboard:** Turn the ignition to the 'on' position (without cranking). Look at the warning lights. Is there a picture of a key or a padlock flashing? This is the immobiliser light. If it's flashing, the car doesn't recognise your key. Your first step should be to try your spare key. If that works, the problem is your main key. If neither key works,
Is it safe to keep driving?
This is a straightforward one: no. You can't drive the car anywhere because it won't start. The more important question is whether it's safe to keep *trying* to start it. The answer there is also generally no, not for long. A few short attempts of 5-10 seconds are fine for diagnosis, but repeatedly cranking a non-starting engine is a bad idea for several reasons: * **You'll flatten the battery:** The starter motor draws a huge amount of current from the battery. If the engine doesn't start and run, the alternator cannot recharge it. Keep cranking and you'll soon end up with a flat battery on t
What a garage will do to fix it
When your car arrives at the workshop on the back of a recovery truck, we'll follow a logical diagnostic process to find the fault efficiently without just swapping parts hopefully. First, we'll connect our professional diagnostic scanner to the car's OBD (On-Board Diagnostics) port. This is usually the very first step. We'll read any fault codes stored in the ECU. A code like 'P0335' points directly to a crankshaft sensor circuit fault, while a 'P0171' (System Too Lean) might suggest a fuel delivery issue. These codes are our primary guide. Next, based on the codes (or lack of them), we'll pe
Typical UK repair costs (2025)
The cost to fix a car that cranks but won't start can vary enormously, as it depends entirely on what has failed. The initial diagnostic check will almost always be a fixed fee. * **Diagnostic Scan:** Expect to pay between **£60 and £120** for a proper diagnostic session with a professional-grade tool and technician's time. This fee is crucial for an accurate diagnosis and often gets absorbed into the final repair bill at good garages. * **Crankshaft Position Sensor:** This is a common and relatively affordable fix. The sensor itself might cost £30-£80, with labour taking it to a total of **£1
My car cranks very slowly and then stops. Is that the same problem? — No, that's a different symptom. A slow crank that struggles and then stops almost always points to a weak or failing battery. Your engine isn't turning over fast enough for it to start. It could also indicate a problem with the starter motor itself or a poor electrical connection to it. A car that 'cranks but won't start' will typically crank over at a normal, healthy speed, it just won't 'catch'
Could cold weather be the cause of it not starting? — Cold weather can certainly be a contributing factor, especially if there's an underlying issue. For diesel cars, the 'glow plugs' that pre-heat the cylinders are critical for a cold start. If they're old and failing, the engine may crank but not fire in low temperatures. For both petrol and diesel, cold weather puts a huge strain on the battery, which can expose a weak battery that might have seem
I can smell petrol after trying to start it. What does that mean? — A strong smell of unburnt petrol usually means the engine is 'flooded'. This happens when the fuel injectors are working correctly, but there's no spark to ignite the fuel. The cylinders fill up with a fuel-air mixture that is too rich to ignite, and the excess petrol vapour is what you can smell. It's confirmation that your fuel pump is likely working, but your ignition system (spark plugs, coils
Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email bob@bobsmechanicalrepairs.co.uk.