P0204

P0204 flags the cylinder 4 injector circuit specifically. On inline-4 engines this is the last cylinder on the bank and often the hottest because it sits closest to the firewall and exhaust manifold collector, which means heat-related connector and harness failures concentrate there. On V8 applications cylinder 4 sits at the rear of bank 1 (driver's side on most domestics). Cheapest-first ladder: noid light to confirm PCM pulse arrival, resistance check at the injector (11-17 ohms port, 1-3 ohms GDI direct injection, compare to the other three cylinders for any outlier more than 0.5 ohm off median), and scope the driver pulse-width which should sit at 2.5 to 3.2 ms warm-idle, climbing to 18 to 22 ms WOT, with a clean square edge and ground-side pull-down within 0.5V of ground. Inspect the cylinder 4 connector for melted plastic and heat-darkened terminals before condemning the injector. The expensive misdiagnosis is replacing the injector for $300 to $500 when a $25 pigtail repair on a melted connector would have fixed it.

Vehicle-specific patterns: 2008-2014 VW/Audi 2.0T (EA888) Jetta, GTI, and A4 throws P0204 from high-pressure direct injector solenoid failure on cylinder 4, often appearing alongside P0301 misfire (VW TSB 24-13-01 covers updated injectors with revised o-rings); 2007-2013 BMW N54 sets P0204 with cylinder 4 piezo injector cracking, addressed by the solenoid-injector retrofit; 2011-2016 Ford 2.0L EcoBoost Focus ST and Escape fouls cylinder 4 GDI tips with carbon, especially on short-trip city use; 2002-2009 Honda Civic D17/R18 fouls or clogs the cylinder 4 port injector and responds well to ultrasonic cleaning for $40 per injector. Estimated repair: $80 to $950.