P2191

P2191 is the bank 2 mirror of P2190 — bank 2 runs RICH at idle specifically, STFT + LTFT pinned at -10% to -25% at warm idle and trims cleaning back up at cruise. Bank-specific plus idle-only narrows the diagnostic the same way P2189 does for lean: causes that affect both banks globally (dirty MAF, failed global FPR, saturated EVAP canister venting into a common plenum) tend to throw P2190 AND P2191 simultaneously, so a solo P2191 points at a fault mechanically isolated to bank 2 — a single leaking bank-2 injector, a bank-2-side purge or PCV path stuck open, a bank-2 fuel-pressure imbalance from a clogged crossover, or coked bank-2 intake valves on direct-injection setups. Cheapest-first: pull the bank-2 plugs and compare against bank-1 (sooty bank 2 + clean bank 1 = diagnostic photo). Scope bank-2 injectors looking for a slow-closer. Check fuel rail balance on dual-rail engines — some V6/V8 designs (Ford 3.5L EcoBoost, GM LT1/LT4) run separate rails per bank and a clogged crossover or failed pressure sensor on one rail throws the other side rich. The at-idle code is the giveaway — leaky bank-2 injector or coked bank-2 intake valves for rich; don't condemn the O2 sensor.

Vehicle-specific patterns: 2011-2017 Ford 3.5L EcoBoost (F-150, Flex, Taurus SHO, Explorer Sport) throws P2191 from a sticking high-pressure fuel pump cam-follower on the bank-2 side and from carbon-coked bank-2 intake valves around 80k-120k miles (no port-injection wash on direct-injection). 2007-2014 GM 5.3L AFM trucks throw P2191 from collapsed AFM lifters dumping crankcase oil into the bank-2 PCV path. 2005-2012 Nissan Pathfinder / Frontier / Xterra VQ40DE 4.0L V6 throws P2191 from a leaking bank-2 injector and from a stuck-open canister purge solenoid that vents to the bank-2 intake. 2008-2014 Cadillac CTS / SRX / STS 3.6L LFX V6 throws P2191 from carbon buildup specifically on the bank-2 intake valves — walnut-blast cleaning around 100k miles is the GM-recommended service. Estimated repair: $60 to $1,400.