Engine Cranks But Won't Start: The Triage a Good Shop Runs First

The starter spins the engine at its usual speed, but it never catches. A crank-no-start invites the parts cannon: fuel pumps, coils and sensors replaced on a guess. Yet an engine needs only four things to run — spark, fuel, compression, correct timing — and a structured triage finds the missing one before any part is ordered. Below: the triage, the pump prime check you can do yourself, and the immobilizer lockout that mimics everything else.

Symptoms to confirm

A true crank-no-start means the engine turns at its normal speed: a single click or silence points instead to the battery, cables or starter. Also watch for faster, freer-than-usual cranking (possible lost compression), no two-second fuel pump hum, a flashing key or padlock light while cranking, or dying right after starting.

• The engine cranks at normal speed. A single click or silence points to battery, cables or the starter — a different diagnosis.
• Cranking that sounds faster or freer than usual — lost compression lets the engine spin easily.
• No two-second hum from the tank area at ignition on.
• A flashing key or padlock light on the dash while cranking.
• It started normally the day before, or starts and dies immediately.
• A fuel smell after long cranking — injectors delivering while spark is missing.

Likely causes, ranked

Five causes are ranked. Fuel delivery failure (dead pump, blown fuse or relay, or an empty tank) is most common, then a crankshaft position sensor fault, which can silently kill spark and injection together and often fails intermittently when hot. Immobilizer lockout is cheapest but costliest to misdiagnose, ahead of ignition failure and, last, timing or compression loss: least common but most urgent.

1. Fuel delivery failure. The most common bucket: a dead pump, failed relay or fuse, faulty pump control module, or — genuinely — an empty tank behind a lying gauge. Relays and fuses cost pocket change; pumps don't, hence the check order.
2. Crankshaft position sensor. If the ECU never sees the crank signal, it commands neither spark nor injection — two essentials gone at once. These sensors often fail intermittently when hot, so the car may restart after cooling.
3. Immobilizer / security lockout. If the key's transponder isn't recognised, the system deliberately withholds fuel or spark on a mechanically healthy engine. The cheapest cause here, and the most expensive to misdiagnose.
4. Ignition system failure. Coils, modules or wiring killing spark across the board. On coil-on-plug engines one bad coil causes a misfire, not a no-start — total spark loss points upstream.
5. Timing or compression loss. A snapped timing belt or jumped chain: least common as a sudden no-start, but urgent — cranking an interference engine can bend valves.

Diagnostic steps (in order)

The order runs cheapest and fastest first, with one thing that comes before all of it. If the engine cranked faster or more freely than usual, stop cranking now and check the timing drive before anything else, and do not treat a quick look as proof: on an interference engine, continued cranking can push pistons into open valves and turn a belt into a cylinder head. Once that is ruled out, scan for codes, listen for the fuel pump's two-second prime, check the security light and try the spare key, then move to the spark test, a fuel pressure check and, if needed, compression.

1. First, if cranking sounded fast or free, stop and check the timing drive. On a belt-driven engine, look through the upper cover: a snapped belt is usually obvious there and costs nothing to check. Treat it as a first indicator and not as proof, because a chain that has jumped or stretched, or a belt that skipped teeth without breaking, can look normal through the cover. If you cannot see clearly that the timing drive is intact, confirm with cam-to-crank correlation or a relative-compression test before cranking again: every test below means cranking the engine more.
2. Scan for codes, even with no warning light. A stored crank sensor (P0335), cam sensor (P0340), fuel pump circuit (P0230) or immobilizer code redirects the diagnosis immediately. No codes doesn't clear the electronics — intermittent sensors don't reliably store one — but a relevant code ends the guessing.
3. Fuel pump prime check. Ignition on, no cranking; listen near the tank for a two-second hum. Hum present: the circuit is alive; suspicion shifts to spark or pressure. Hum absent: check fuse and relay before anyone condemns the pump.
4. Check for the security light. A flashing key or padlock symbol during cranking means the immobilizer is refusing the key. Try the spare key; if the car starts, the fault is the key or antenna ring, not the engine. Skipping this step is how immobilizer faults end up wearing new fuel pumps.
5. Spark test. An inline spark tester on one coil or lead while cranking. Spark present rules out the ignition side. No spark and no injector pulse together point strongly at the crank sensor or its wiring — one upstream fault, not two coincidences.
6. Fuel pressure test. A gauge on the rail (or live scan-tool data) during cranking confirms whether fuel actually arrives at spec. Well below spec with a humming pump suggests a failing pump, blocked filter or regulator fault.
7. Compression check. If cranking sounds wrong or everything above passes, a compression test — or a scope relative-compression test, no disassembly needed — confirms the mechanical side.

What a fair repair should cost

The spread is enormous — exactly why the triage matters. At the cheap end, a pump relay or fuse is a tens-of-euros fix and a crank sensor typically low hundreds fitted, depending on access. A fuel pump commonly runs a few hundred euros fitted — in-tank access varies by model. Immobilizer fixes range from a free spare-key test to key programming in the low hundreds. The expensive end is timing failure: a belt replacement is a hundreds-of-euros job, but valve damage on an interference engine pushes into the thousands. An hour of structured diagnosis is the cheapest line on any of these invoices. If a quote names a part without the prime check, spark test or pressure reading that condemned it, ask for the evidence.

The takeaway

No parts should go on a crank-no-start until the shop can show you which of the four — spark, fuel, compression, timing — is missing.