P0168

P0168 means the fuel temperature sensor is reading above the upper threshold — typically more than 200F sustained, which on a gasoline FFV (flex-fuel vehicle) or diesel system signals that the fuel is dangerously hot and the ECM may de-rate fuel pressure or injector pulse-width to prevent vapor lock or injector damage. Fuel temperature matters most on returnless systems (where hot fuel cycles back through a heat-soaked tank), on diesels (where injector timing compensates for fuel density which varies with temperature), and on FFVs (where ethanol-gasoline blends have different vapor-pressure curves). Normal operating fuel temp is roughly 60-150F at the tank, climbing to 150-200F at the rail under hot-soak idle in summer; sustained readings above 200F mean either the sensor is failed-high, the fuel return path is restricted, the tank is sitting on hot exhaust components, or there's an actual heat problem. Cheapest-first ladder: scan live fuel temp data, then verify with an infrared thermometer on the fuel rail and return line — if the scan tool reads 220F and the IR reads 90F, the sensor or its wiring is failed-high; if the scan tool and IR agree, the heat is real. Backprobe the sensor signal wire (typical 2-wire NTC thermistor in the tank or on the rail) — at 100F it should read roughly 2.5-3.0V, at 200F roughly 0.8-1.2V; a flat low reading means the sensor is shorted internally. Expensive-misdiagnosis caveat: a clogged return line or kinked tank-to-pump hose can produce a genuine 200F+ reading and the sensor is correctly reporting it — don't blame the sensor before checking return-line flow rate.

Vehicle-specific patterns: 2002-2010 Ford F-150 FFV and Explorer FFV with the 4.6L/5.4L flex-fuel system commonly throws P0168 from the in-tank fuel temp sensor reading drift after E85 corrosion of the sender housing — Ford redesigned the sender assembly mid-cycle. 2005-2011 GM Impala/Monte Carlo FFV with the 3.5L/3.9L flex-fuel V6 throws P0168 from the fuel temp element inside the in-tank fuel pump module degrading; the fix is a full pump module swap. 2003-2008 Chrysler Sebring/Stratus FFV with the 2.7L V6 throws P0168 from harness chafe at the fuel-tank-to-frame transition. 2008-2014 RAM 2500/3500 6.7L Cummins throws P0168 from the fuel-rail-mounted temp sensor failing internally after long-haul hot-soak duty cycles. Estimated repair: $150 to $550.