P0291

P0291 sets on V12 engines only and indicates the cylinder 11 injector circuit is reading low (short to ground or internally shorted winding). Cheapest first: swap injector 11 with a known-good neighbor and clear codes; on Mercedes M275/M279 and BMW N74 these are GDI high-pressure solenoid injectors that ohm at 1.5 to 4 ohms cold, with shorted windings reading under 1 ohm. On Lamborghini L539 and Ferrari V12 platforms the injectors are also GDI in modern years (post-2011) and follow the same range. With the connector unplugged and key on, the driver-side pin should be open to ground; continuity to chassis ground confirms a harness short. Caveat: BMW N74 and Mercedes M275/M279 use separate injector driver modules; a failing IDM channel will set cylinder-specific low codes with no harness or injector fault, and the modules are bank-specific so swapping the bank-1 and bank-2 IDMs is a near-free diagnostic if you can access them.

Vehicle-specific patterns: 2003 to 2014 Mercedes-Benz S600/SL600/CL600 M275/M279 twin-turbo V12 has known HDEV-5/HDEV-6 injector winding failures and IDM channel weakness around 80k to 120k miles; 2009 to 2015 BMW 760i N74 V12 has documented injector driver module faults per BMW service bulletin SI B12 09 13; 2011 to 2017 Lamborghini Aventador L539 V12 has cracked injector connectors from sustained underhood heat. Estimated repair: $180 to $2,400.