Starting, battery and electrics
Car slow to start: causes and what to do
A car that cranks slowly, or cranks for a long time before it fires, usually has a weak battery, loses fuel pressure while parked or, on a diesel, has glow plugs that no longer heat. It often gets worse in the cold.
Check without hurryStarting, battery and electrics
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Usually not urgent, but do not ignore it. It is rarely urgent, but it is a warning: it usually ends in a car that will not start. Have it checked before winter or a long trip.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Weak battery: the engine turns more slowly than normal, especially when cold.
- Loss of fuel pressure: a check valve or a dripping injector empties the system while the car is parked.
- Glow plugs on a diesel: one or more blown glow plugs or their control unit.
- Coolant temperature sensor: if it reports the wrong temperature, the control unit meters fuel badly on start-up.
- Air in the diesel system: air getting in after a filter change or through a seal.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: What do the crankshaft and camshaft sensors do and what happens when they fail? How can you tell if the 12 V battery is failing? What does the engine thermostat do and what does P0128 mean?
Car system: Ignition
What you can check yourself
Notice whether it cranks slowly (battery) or cranks normally but takes long to fire (fuel or ignition).
Try switching the ignition on, waiting a few seconds and then starting: if it improves, it points to fuel pressure or preheating.
On a diesel, see whether the glow plug light goes out sooner than usual or flashes.
Check when the fuel filter was last changed.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
- P0087Fuel rail/system pressure: too low (bank 1)
- P0190Fuel rail pressure sensor (bank 1), circuit: malfunction
- P0335Crankshaft position sensor A, circuit: malfunction
- P0380Glow plug/heater, circuit A: malfunction
- P0671Cylinder 1 glow plug, circuit open
- P0118Engine coolant temperature sensor 1, circuit: signal high
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: system voltage while cranking, fuel pressure, coolant temperature and preheating status.
Frequently asked questions
Why does it take longer to start in the cold?
In the cold the battery delivers less current and fuel atomises worse; any weak part shows sooner.
It is slow to start when hot. What could it be?
When hot, fuel pressure loss, a temperature sensor or the crankshaft sensor are more likely.
Can I use a starting spray?
It is not advisable, especially on diesels with glow plugs: it can damage the engine. Find the cause.
Keep reading
- Engine ignition: how it works and what fails
- Glow plug light on or flashing: what to do
- Engine cranks but will not start: causes and what to do
- Car stalls by itself: causes and what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means