Diagnostic: Black smoke on BMW - Causes and costs

Black smoke from the exhaust of a BMW (1 Series, 3 Series, 5 Series, X1, X3) 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.

BMW diesel (B47, B57)

On B47 and B57 engines, black smoke is often linked to a blocked particulate filter (DPF) or a faulty injector. A saturated DPF can cause black smoke under acceleration. A leaking or misadjusted injector also produces black smoke. Other possible causes: turbo (leak, geometry), lambda sensor, clogged EGR valve.

BMW petrol (B38, B48)

On B38 and B48 (turbo petrol), 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: about €80–200. DPF replacement: €900–2,000 and more.
• Diesel injector: about €350–700 per injector. Turbo: €1,000–2,500 depending on engine.

My Auto Check-up helps you prepare your visit by describing symptoms for an initial estimate.