P0140

P0140 means bank 1 downstream sensor (B1S2) shows NO activity — the signal sits flat at bias voltage and never moves, even under conditions (decel fuel cut, throttle snap, cat-monitor test) where a working downstream sensor should show some movement. Like P0134 upstream, this often pairs with a heater fault (P0141), because a cold sensor produces no signal at all. Cheapest-first: ohm the heater pins (spec 6-15 ohms narrow-band cold) — open circuit means sensor heater failed. If heater is in spec, verify the ECU is providing bias voltage (key-on engine-off, ~0.45V at the signal pin). If bias is there but no activity once warmed up, the element is dead. Note that on cars with cylinder-deactivation or aggressive lean-burn modes (GM AFM, Honda VCM, Chrysler MDS), the downstream may legitimately sit quieter than the upstream and the ECU has wider tolerance — so a P0140 only sets when the signal is truly inert.

Vehicle-specific patterns: 2004-2008 Ford F-150 5.4L 3V throws P0140 routinely past 120k miles — Motorcraft downstream sensors degrade in cold-weather salt environments. 2006-2013 Chevy Impala / Malibu 3.5L/3.9L sets P0140 when the downstream harness chafes against the catalytic converter shield. 2005-2012 Toyota Avalon / Sienna 2GR-FE throws P0140 after a cylinder-deactivation event damages the downstream element with quench. 2007-2014 Nissan Murano / Pathfinder VQ35 sets P0140 from a TSB-noted Bosch sensor lot (Nissan campaign extended warranty on affected VINs). Cost band: $150-$350 for sensor + labor; under $80 if it's a chafed wire repair.