P0468

P0468 is the inverse of P0467 — the ECM sees the purge flow sensor signal pinned HIGH (typically above 4.7V) when commanded duty cycle doesn't justify it, OR even with purge solenoid commanded fully closed. Either the sensor element is biased high from contamination, the signal wire is shorted to 5V reference or battery voltage, or the sensor is correctly reporting genuine high flow because the purge solenoid is stuck open and dumping unmetered vapor into the intake. Cheapest-first ladder: (1) Backprobe the purge flow sensor signal pin KOEO — if it reads 4.8-5.0V with no engine running, the signal wire is shorted high (chafe against a hot lead) or the sensor's internal pull-up has failed. (2) Disconnect the sensor; if signal voltage at the ECM pin drops to 0V with the connector unplugged, the sensor is biased internally — replace it. If voltage stays at 4.8V+ with the sensor unplugged, the wire is shorted to a power source — trace the harness. (3) Verify the purge solenoid isn't mechanically stuck open by removing the vacuum line and watching for vapor flow with key-off; a stuck-open solenoid lets the sensor see real high flow with zero command, which sets P0468 from a sensor-perspective even though the sensor is innocent. (4) Inspect the sensor element for oil/carbon contamination biasing the hot-wire reading. Before condemning the purge flow sensor, check whether the carbon canister is recently saturated — liquid fuel coating the sensor element biases it artificially high and clears after a few days of vapor-only purge cycles ($0 fix vs. $400 part).

Vehicle-specific patterns: 2009-2014 Volvo S60/XC60 throws P0468 from purge solenoid diaphragm failure letting unmetered vapor through with zero command — sensor reading is accurate, solenoid is the actual fault. 2011-2017 Hyundai Sonata/Tucson/Santa Fe GDI throws P0468 from oil-saturated sensor elements after extended idling cycles overload the carbon canister. 2010-2015 Kia Sorento/Optima GDI shares the pattern. 2008-2014 Ford F-150 EcoBoost 3.5L throws P0468 from harness chafe near the intake manifold where the signal wire rubs against a hot exhaust shield and shorts to 12V intermittently. 2007-2012 Volvo S40/V50/C30 throws P0468 from a sensor internally biased high after coolant intrusion via a leaking thermostat housing nearby. Estimated repair: $130 to $470.