P0261

P0261 sets when the ECM driver detects current through the cylinder 1 injector circuit below the expected threshold during pulse-width commands, indicating a short to ground on the injector low-side circuit, a shorted injector winding pulling excessive current, or a failed ECM injector driver. Cheapest-first ladder: with the engine off and key on, unplug the cylinder 1 injector and ohm the injector coil across its two pins — a healthy saturated-driver injector reads 11-17 ohms (Bosch EV6/EV14 typical), a peak-and-hold low-impedance reads 1.5-4 ohms; reading under 1 ohm confirms a shorted winding. Inspect the harness from the injector connector back along the intake manifold and against the cylinder head for chafe spots — the cylinder 1 injector harness on V-engines often runs against the timing cover edge. Use a noid light or current-clamp on the injector control wire to confirm the ECM is still attempting to fire; if no pulse is present after the harness checks clean, the ECM driver has failed. Caveat: P0261 will not always set a misfire code immediately because the ECM may disable the driver to protect itself — do not assume the cylinder is firing just because the engine runs.

Vehicle-specific patterns: 2007-2013 Chevy Silverado/Tahoe 5.3L (LMG/LC9) — injector harness chafe against the intake manifold mounting boss on cylinder 1, repair harness and apply protective loom; full injector replacement (Multec part 12613411) only if winding ohms confirm short. 2005-2010 Ford F-150 5.4L 3V — injector connector pin corrosion on cylinder 1 from valve cover gasket seep, clean and replace pigtail. 2006-2012 Toyota Tacoma 4.0L (1GR-FE) — cylinder 1 injector internal short under TSB EG028-09, replace injector 23250-31020. 2007-2013 Dodge Ram 1500 5.7L Hemi — injector driver failure inside PCM on bank 1, PCM replacement and reflash with security key. Estimated repair: $80 to $900.