Diagnostic: Black smoke on Renault - Causes and Cost

Black smoke from the exhaust of a Renault (Clio, Megane, Scenic, etc.) usually indicates over-fuelling (too much fuel relative to air) or a combustion problem. Depending on the engine (petrol or diesel), causes and costs differ.

Renault diesel (dCi)

On dCi engines (1.5 and 1.6), black smoke is often linked to a blocked diesel particulate filter (DPF) or a faulty injector. A saturated DPF prevents proper evacuation of gases and can cause high consumption and black smoke under acceleration. An injector that is leaking or out of adjustment sends too much fuel into the cylinder and also produces black smoke.

Other possible causes: turbo (seal or geometry fault), lambda sensor, clogged EGR valve. High mileage increases the likelihood of these failures.

Renault petrol (TCe)

On TCe (turbo petrol) engines, black smoke can come from a turbo leak (oil), a faulty MAF sensor or an injection system that is poorly adjusted. Prolonged over-fuelling can damage the catalyst and DPF (if fitted).

Indicative costs

• DPF clean / regeneration: around €80 to €200 (depending on garage and procedure).
• DPF replacement: €800 to €1,800 (parts and labour).
• Injector (diesel): around €300 to €600 per injector (parts and labour).
• Turbo: €1,000 to €2,500 depending on engine.

An electronic diagnosis and checks of pressures (turbo, DPF) help pinpoint the cause. My Auto Check-up helps you prepare the useful information (when it appears, engine, mileage) to estimate costs before your garage visit.