P0073

P0073 is the specific ambient air temperature sensor circuit HIGH INPUT fault — the inverse of P0072. The PCM is seeing AAT signal voltage pinned at or above the high-voltage threshold (typically above 4.5-4.9V, which scales to a temperature reading at or above the 248 F ceiling of the sensor table), which physically means either the signal wire is open (broken between sensor and PCM), the sensor connector is disconnected, the sensor itself has failed open internally, or the signal wire is shorted to the 5V reference. Cheapest-first ladder: (1) Scan live data and confirm AAT is pegged at the 248 F ceiling — that confirms a hard-open circuit, not a drift fault. (2) Locate the sensor (bumper, mirror, behind grille per vehicle) and confirm it's still physically attached and connected — disconnected sensors from car-wash strikes or amateur bumper-cover R&R are #1 cause. (3) With sensor unplugged, jumper the two pins of the connector together; if AAT now reads the 248 F ceiling AND the high-input code stays, the harness signal wire is open between connector and PCM; if AAT now flips to the -40 F floor, the harness is fine and the sensor was open internally. (4) Ohm-out the sensor against the OEM thermistor table (typically 9-12 k-ohm at 32 F, 2-3 k-ohm at 70 F) — infinite resistance confirms a dead sensor. (5) Swap the sensor ($15-50) and clear. The expensive misdiagnosis: don't condemn the PCM or the instrument cluster (which displays AAT) before doing the connector-jumper test — a broken connector latch that lets the sensor fall partway out is invisible from above and sets P0073 even though the sensor itself is fine.

Vehicle-specific patterns: 2009-2014 Ford F-150 and 2008-2016 Ford SuperDuty set P0073 most commonly from a sensor that's been knocked loose by a winter bumper strike or by car-wash brushes catching the harness — the connector backs out of the sensor body and reads open. 2007-2014 GM full-size trucks (Silverado, Sierra, Tahoe, Yukon) set P0073 from the bumper-mounted sensor harness being cut during off-road use or by tow-strap routing. 2008-2015 Dodge Ram and 2011-2018 Jeep Grand Cherokee/Dodge Durango set P0073 from grille-area harness fatigue at the grommet pass-through. 2007-2013 Mercedes-Benz GL/ML/R-Class mounts the AAT in the front bumper behind the lower grille and sets P0073 frequently after front-bumper R&R where the harness gets pinched or left disconnected. Estimated repair: $15 (sensor swap DIY) to $350 (sensor + harness repair + connector + labor at shop).