Car won't start: causes and step-by-step checks | DVI Reports

Car won't start: causes and step-by-step checks

The first step is to find out whether the starter turns the engine. If not, the cause is usually the battery or the starting circuit; if it turns but will not fire, look at fuel, the crank sensor or the immobiliser.

First distinguish no cranking from an engine that cranks but does not start. Sound alone does not confirm a failed part.

General guidance, not a confirmed diagnosis for a make. Provide the model, year, engine and when the symptom occurs.

Possible causes

• Discharged battery, electrical connections or starter faults.
• Insufficient fuel supply.
• Ignition, sensor or immobiliser faults.

What to check

• Record clicks, whether the engine turns and any dashboard messages.
• Check fuel availability and have the battery and starting circuit tested.
• Record whether it happens cold, hot or after standing, and whether you are using the spare key.

Diagnostic steps, in order

1. Step 1: Listen to the starter

   Nothing or just a click: battery, terminals, starter or, on an automatic, the selector not in P or N. Cranks normally but will not start: fuel, ignition, sensors, immobiliser.

2. Step 2: Check the battery

   With a multimeter, a charged battery shows about 12.6 V at rest; it should not drop far below 10 V while cranking. Clean and tighten the terminals.

3. Step 3: On an automatic gearbox

   Start with the selector in P, then try N with the brake pedal pressed. If it only starts in N, the selector position sensor or brake switch may be the cause.

4. Step 4: Read the codes

   P0335 (crankshaft sensor) can stop the engine starting altogether; P0340 or P0016 point to camshaft/crankshaft timing; P0087 means low fuel pressure. Check immobiliser messages too.

5. Step 5: Check the fuel supply

   Listen for the fuel pump when you switch the ignition on (a short hum). On a diesel that ran dry, the system must be bled according to the manual.

   Warning: Do not keep cranking for long: the starter overheats and, on petrol engines, unburnt fuel can damage the catalytic converter.

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Avoid repeated cranking. Stop attempts and seek assistance if smoke or a burning smell appears.

The symptom alone does not establish a DTC or failed part. Save stored codes and scan data before clearing them.

• The AA — starting problems
• The AA — starter motor

OBD codes to investigate when actually reported

A symptom does not imply a code. Follow a link only when your scanner actually reports it.

Symptoms and warning lights

Related guides

Reduced power can come from the engine or transmission. A protection mode is a response to a problem, not a diagnosis.

A guide to 16 common dashboard lights: how to recognise them, what they can mean and when to stop safely.

Separate an engine that does not crank or cranks slowly from one that cranks normally but will not start. Record ambient temperature and parking duration: a cold engine does not necessarily mean freezing weather.

Cold-start vibration may result from irregular combustion, fuel delivery or engine mounts. Distinguish unstable RPM from vibration at steady RPM.