P0275

P0275 means the ECM is running cylinder-balance monitoring and has determined that cylinder 5 is contributing less torque (or in some calibrations, more torque) than the average of the other cylinders by more than the manufacturer's threshold — typically a deviation of more than 5 mm3/stroke on the per-cylinder injector trim values that the ECM continuously adjusts to equalize crankshaft acceleration between firing events. Normal cylinder balance trims sit between -3 and +3 mm3/stroke at idle; anything past +/- 5 mm3 for a sustained period sets the code. Cheapest-first ladder: scan live injector balance / cylinder contribution data — most modern OE scan tools and many enhanced aftermarket tools (Snap-On, Autel MaxiSys, Texa) display per-cylinder fuel correction in real time. A cylinder reading +6 to +10 mm3 is being commanded extra fuel to keep up, meaning it's mechanically weak (low compression, valve issue, injector flowing low). A cylinder reading -6 to -10 mm3 is being pulled back because it's making more torque than expected, meaning a stuck-open injector or a fuel-volume leak past a seal. Next: dead-cylinder cutout test, then a wet/dry compression check on cylinder 5 (looking for less than 85% of the highest cylinder), then an injector flow test or click-test current waveform on a scope. Expensive-misdiagnosis caveat: don't replace the injector before verifying compression — on direct-injection and diesel engines, a worn or stuck valve will mimic an injector contribution fault exactly, and you'll burn $300-$800 on an injector that doesn't fix the code.

Vehicle-specific patterns: 2003-2007 Ford 6.0L Powerstroke (F-250/350, Excursion) throws P0275 constantly when injector stiction sets in around 100k miles — the spool valves in the HEUI injectors stick from cold-start cycles and one cylinder contributes erratically; the fix is a $1,500-$3,500 injector set, often combined with an oil cooler / EGR cooler service. 2001-2004 Chevy/GMC Duramax LB7 6.6L has a well-documented injector failure on the rear cylinders specifically (cylinder 5 and 7 on the left bank) — GM extended the warranty to 200k miles on LB7 injectors and the fix is replacing all 8. 2011-2016 RAM 2500/3500 with the 6.7L Cummins commonly throws P0275 from a failed CP3/CP4 pump putting metal contamination through the rail and damaging individual injectors. 2008-2014 BMW N63 4.4L twin-turbo V8 throws P0275 from index-code mismatch after injector swaps without recoding, or from carbon-fouled intake valves causing uneven airflow on the right bank where cylinder 5 lives. Estimated repair: $150 (single coil/glow plug + injector clean) to $4,500 (full injector set on a 6.0L Powerstroke).