A4 B9 TDI power loss with black smoke usually means too much fuel or not enough clean air.
EGR and DPF clogging are common culprits—here’s how to diagnose it safely.
What black smoke under load is telling you
On your Audi A4 B9 diesel—especially the 2.0 TDI—black smoke under load is unburnt soot. That means the engine is getting more fuel than it can burn with the air available. When you add load (uphill, overtaking, towing), the ECU asks for more fuel, but a restricted intake, sticky EGR, clogged DPF, or weak turbo boost leaves it short on oxygen. The result is power loss, a sickly haze, and often a stored fault code or limp mode.
