P0203

P0203 isolates the fault to the cylinder 3 injector circuit, with the same electrical logic as P0201 and P0202: the PCM saw an open, short, or driver-circuit anomaly on injector 3's pulse and flagged that cylinder specifically. On inline-6 and V-configuration engines, cylinder 3 sits in the middle of one bank, which makes it a common heat-soak victim on engines where the intake routing puts the boost intercooler return or exhaust crossover near that injector's pigtail. Cheapest-first ladder: noid light test at the cylinder 3 connector to confirm PCM commands a pulse; resistance check at the injector (port: 11-17 ohms, GDI: 1-3 ohms) and compare to the other five or seven cylinders, looking for any injector that reads more than 0.5 ohm off the median; scope the ground-side waveform for a clean pull-down to within 0.5V of ground; finally, swap with another injector on the same bank and see if the code follows. The expensive misdiagnosis is replacing all six injectors on a BMW N54 at $1,800 to $2,400 when the actual failure is a single $280 injector that needs to be index-coded via ISTA.

Vehicle-specific patterns: 2007-2013 BMW N54 335i sets P0203 commonly because cylinder 3 is in the middle of the head and runs slightly hotter under boost, and the piezo-electric injector (in early N54 cars before the solenoid retrofit under SIB 13 01 09) develops cracked piezo stacks; 2011-2017 Ford 3.5L EcoBoost Explorer and F-150 throws P0203 from carbon-tip buildup on the middle cylinders that disrupts spray pattern; 2007-2013 GM 5.3L LS trips P0203 from melted-connector syndrome where exhaust heat from the manifold deforms the Multec injector connector body; 2003-2007 Honda Accord V6 J30/J35 sees P0203 from a clogged port injector that responds to a $90 BG fuel-induction service. Estimated repair: $90 to $2,400.