Car turns over but won’t start: fuel, spark or signal?

Updated 23 July 2026 · OBDCode UK editorial

If the engine turns over at normal speed but will not fire, the starter is doing its job. The missing ingredient is usually fuel pressure, ignition, or an engine-position signal. Scan first: P0335/P0340, fuel-pressure and immobiliser clues can prevent hours of guessing.

Can you keep driving?

The car is already stationary, so avoid flattening the battery with repeated cranking. Stop immediately if you smell strong petrol, see smoke, or hear mechanical clashing. After two or three short attempts, diagnose rather than keep trying.

Match what the car is doing

What you notice	Most likely	How to separate it
Cranks normally; rev counter never moves	Crankshaft-position sensor or signal	P0335/P0336 and live RPM while cranking are stronger evidence than the rev-counter alone.
Starts briefly with jump assistance	Battery voltage collapses under cranking	A battery can spin the engine yet pull ECU voltage too low; test cranking voltage and CCA.
Diesel is worst cold, then runs normally	Glow plugs, relay or weak battery	P0380/P067x may be stored; compare cranking speed and glow-current test.
No fuel-pump sound and low rail pressure	Pump, relay, fuse or pressure fault	Check pressure data and power at the pump before condemning it.
Key/immobiliser message on dash	Key recognition or immobiliser fault	Try the spare key and scan the body/immobiliser module with a capable tool.

Checks to do before buying parts

Watch battery voltage while cranking; slow cranking changes the diagnosis.
Read engine and, if possible, immobiliser modules. See what a proper diagnostic should include.
Check fuel level rather than trusting a suspect gauge, and listen for the normal pump prime.
Do not use starting spray on modern diesels or engines with intake heaters unless the manufacturer procedure explicitly allows it.

Typical UK costs

Likely job	Typical fitted price
Battery/connection fix	£0–£350
Crank or cam sensor fitted	£100–£300
Glow plugs/relay	£120–£450
Fuel-pump or rail-pressure repair	£250–£1,000+

Indicative 2026 independent-garage prices for mainstream cars; London, prestige, SUV and seized-part jobs can cost more. Diagnose first.

MOT relevance

A non-starting vehicle cannot complete an MOT. More importantly, the warning lamp or emissions fault behind the no-start may remain a test issue after the engine runs.

Tools that help with this check

TOPDON BT100 battery tester12V battery health and cranking test in 10 seconds
MotoPower battery testersBattery and charging-system testers for DIY checks

Frequently asked questions

Why won’t my car start even with a new battery?

A new battery only solves low cranking power. If it turns normally, check crank/cam signal, fuel pressure, ignition and immobiliser data.

Can a crank sensor fail without an engine light?

Yes. An intermittent no-start can occur before a permanent lamp appears, but a pending code or zero RPM in live data while cranking may reveal it.

Sources and further reading

General guidance for UK drivers, not professional advice. MOT rules follow the DVSA inspection manual (2026 edition).