P0274

P0274 indicates the PCM detected an electrical fault on the cylinder 5 injector driver circuit reading high voltage, which typically means the circuit is open or the driver is not pulling the line to ground when it should. Start with the cheapest test: swap injector 5 with a known-good injector from another cylinder (most commonly cylinder 1 or 7) and clear codes; if the code follows the injector you have a bad solenoid winding. If it stays on cylinder 5, back-probe the injector connector and measure winding resistance, which should read 11 to 17 ohms on a port-injection (PFI) coil-type injector and 1.5 to 4 ohms on a GDI solenoid type at 68F. Next, key-on engine-off, check that the 12V supply side of the connector reads battery voltage and that the driver wire shows the PCM pulling it low briefly during a cylinder contribution test; expected injector pulse width at warm idle is 2.5 to 4.5 milliseconds on a port-injected V8 and 0.3 to 0.6 ms on GDI. Caveat: never probe the driver wire with a test light powered from B+, because that backfeeds the PCM driver and can permanently kill the channel; use a noid light or scope only.

Vehicle-specific patterns: 2004 to 2008 Ford F-150 5.4L 3V triton trucks often set P0274 from chafed injector harness where the engine wiring loom rubs the right-side valve cover stud, repaired by re-routing and adding spiral wrap; 2005 to 2007 Jeep Grand Cherokee 5.7L Hemi has a known cracked solder joint inside the injector connector body documented in TSB 18-040-07 for the original Bosch injectors; 2007 to 2013 GM 5.3L LMG/LC9 trucks suffer driver-side bank 2 harness melt near the exhaust manifold heat shield. Estimated repair: $35 to $480.