Car won't start in cold weather
A no-start that only happens in frost usually comes down to whichever system was already closest to its limit losing the last bit of margin to the cold: a tired battery can't deliver enough current, thick oil adds drag, or marginal ignition and fuel components simply stop working below a certain temperature. A slow, labouring crank points to the battery or starter, while a normal crank with no firing points to spark or fuel.
Urgency
Visit a workshop soon
Possible causes, most likely first
- Weak or ageing 12V battery
Cold cuts a battery's effective capacity roughly in half; a battery that still starts the car in summer may not turn the starter over in winter. Check rest voltage (above 12.4V) and cranking voltage (shouldn't drop below ~9.6V); a battery over 4-5 years old is a prime suspect. - Corroded or loose battery terminals
Thin corrosion or a loose clamp adds resistance that only becomes critical at high cranking currents. Wiggle-test the clamps and look for white or green crust; clean and retorque. - Engine oil too thick or wrong grade for winter
Using the wrong viscosity or very old, thickened oil makes the starter struggle to turn the engine fast enough to fire. Check the dipstick for oil matching the manufacturer's winter spec, e.g. 0W-30 instead of 15W-40. - Worn starter motor or high-resistance starter cable
A starter that works fine when warm may struggle when cold grease in the bendix or bearings thickens. Listen for a single click or a slow, labouring crank rather than a sharp one. - Weak spark from worn spark plugs or a failing coil (petrol)
Cold makes a marginal ignition system fail to fire at all; plugs due for replacement or a weakening coil pack show up first on frosty mornings. - Immobiliser or key fob fault made worse by cold
Cold reduces the range and reliability of a key fob; an immobiliser that doesn't recognise the key leaves the starter disabled with no cranking at all.
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What you can check yourself
- Turn on headlights before cranking; if they dim dramatically or go out, suspect the battery.
- Listen to the crank: slow and labouring points to battery or starter, a single click with no crank points to battery or connections.
- Hold the key fob directly against the start button or ignition if the immobiliser light flashes.
- Check the oil dipstick for correct winter-grade oil and a clean, not sludgy, appearance.