2003 VW Passat P0171 P0300 P0301 P302 P304 P411 - Hesitation at 20-30 mph and Misfire Codes After Recent Repairs
My mother drives a 2003 VW Passat 1.8L 4-cylinder model, which is currently displaying multiple OBD-II diagnostic codes: P0171 (Rich or Lean Fuel Mix), P0300 (Random/Multiple Cylinder Misfire), P0301 (Cylinder 1 Misfire), P302 and P304 (Specific cylinder misfires), and P411 (Secondary Air Injection System Malfunction). The vehicle hesitates noticeably when accelerating from 20 to 30 mph. A mechanic previously suggested replacing the engine control module (ECM), but I'm seeking additional insights before scheduling another visit. Recently, we replaced the spark plugs, cylinder #2 fuel injector, and air filter—yet the codes persist. Could these issues be related? Is there a specific component or system that should be inspected first to resolve all codes simultaneously?
The P411 code is likely contributing to the other symptoms. A malfunction in the secondary air injection system can cause the fuel mixture to lean out, which may trigger both P0171 (lean condition) and misfire codes like P0300, P0301, P302, and P304. If recent repairs—such as spark plug or injector replacements—have resolved symptoms temporarily but the same codes reappear, it suggests the underlying issue remains unresolved. In such cases, the mechanic may be responsible for a follow-up inspection or repair.