Car hard to start or won't start: causes and affected cars

An engine that struggles to start, cold or hot, has no single cause: the injection, the battery and electronics, or a mechanical part such as the flywheel can be to blame. Hard starting with smoke, jerking or an engine warning light points to the injection.

Injection (mostly on diesels)

This is the most cited cause. On the Mercedes C-Class W203 C 220 CDI, hard starting or jerky acceleration can betray costly injector problems (CarVerif). The piezo injectors of 2000s-2010s Mercedes CDI engines gradually stick, causing hard cold starts, misfires and black smoke (CarVerif). On the Renault Laguna III 2.0 dCi, injector wear appears between 70,000 and 110,000 km for a bill of €600 to €900 (CarVerif).

A car that starts badly after short trips but better after a long drive calls for a check of charging, the fuel rail, the injectors and the particulate filter (CarVerif, Mercedes A-Class).

The dual-mass flywheel

On the Ford Focus 1.8 TDCi, the dual-mass flywheel is known to be weak in town use; it causes hard starting both cold and hot (Fiches-auto).

Battery and electronics

A weak battery is the first suspect when the starter turns slowly or just clicks: see battery draining. But electronics can also prevent starting: a Jaguar XE owner describes a "click click" with no start, where the battery was not to blame (Fiches-auto). On the Dacia Spring, a sealing fault in the charger fuse cover led to a service campaign for a "Panne électrique danger" message preventing starting (L'argus).

Before buying a used car

Start the car yourself from cold. Hard starting, an engine warning light or an outstanding recall are reasons to walk away (CarVerif, Hyundai i10 III; CarVerif, Peugeot 208 I).