P0270

P0270 indicates the ECM has measured cylinder 4 injector circuit current below the expected threshold during commanded firing pulses, pointing to a shorted injector coil, a short to ground in the injector low-side harness, or a failed ECM injector driver. Cheapest-first ladder: ohm the cylinder 4 injector with the connector unplugged — 11-17 ohms is healthy for saturated-driver injectors, 1.5-4 ohms for low-impedance peak-and-hold; anything appreciably below the low spec confirms winding shorted-turns. Check harness routing — on inline-4 engines cylinder 4 is at the rear of the valve cover where it crosses the firewall brackets and brake-booster vacuum line, and on V-engines cylinder 4 may be either front-bank or rear-bank depending on manufacturer numbering, so verify FSM cylinder ID before tracing. Use a noid light or current clamp to confirm the ECM is still pulsing the driver; verify 12 V supply on the injector feed. Caveat: on Honda K-series and Toyota 2AR engines the cylinder 4 injector connector sits directly under valve-cover breather hose drips, so connector corrosion mimics circuit-low for several thousand miles before fully failing — inspect connector pin condition before condemning the injector.

Vehicle-specific patterns: 2006-2011 Honda Civic 1.8L (R18A1) — cylinder 4 injector connector corrosion from valve cover breather drip, clean pins and replace pigtail before full injector. 2007-2014 Toyota Camry 2.5L (2AR-FE) — internal injector winding short, replace 23250-0H050. 2005-2010 Subaru Impreza/Forester 2.5L (EJ253) — injector harness chafe against the boxer engine bracket near the rear bank, repair and reloom. 2008-2013 GM Equinox/Terrain 2.4L (LAF/LEA) — cylinder 4 injector internal short under GM PIP5235, replace 12638530. Estimated repair: $80 to $480.