P0070

P0070 is the generic ambient air temperature (AAT) sensor circuit fault — the PCM has decided the AAT sensor reading is outside the rationality window, either because the voltage is implausible relative to other temperature sensors (intake air, engine coolant, transmission fluid) or because the signal is intermittent enough to fail the continuous-monitor test. The AAT sensor is a thermistor that reads 0.5-4.5V scaled across roughly -40 to 248 degrees F, so cheapest-first: (1) Scan AAT live data with the engine cold (sat overnight) and compare against ECT and IAT — all three should agree within 5-10 degrees F at cold-soak. If AAT reads -40 F on a 70 F morning, the sensor or its wiring is open; if it reads 248 F, the signal is shorted to ground or to another circuit. (2) Inspect the sensor itself — on most modern vehicles it's mounted in the front bumper, behind the grille, or in the mirror housing, where it's exposed to road salt, debris strikes, and winter freeze-thaw cycles; corrosion at the connector and physical damage are the top two failure modes. (3) Ohm-out the sensor against the OEM thermistor table (typically 9-12 k-ohm at 32 F, 2-3 k-ohm at 70 F, 300-500 ohm at 200 F) — anything outside the table is a bad sensor. (4) Wiggle-test the harness from the sensor back to the PCM at the connector and any pass-through grommets — intermittent breaks set P0070 and clear themselves before the tech can see the fault. The expensive misdiagnosis: don't replace the body control module or instrument cluster (which displays the AAT reading) before testing the sensor itself — many shops chase a stuck outside-temp display on the cluster to a $400 BCM when the $15 sensor was the cause.

Vehicle-specific patterns: 2009-2014 Ford F-150 and 2008-2016 Ford SuperDuty (F-250/F-350/F-450) mount the AAT sensor in the driver-side mirror housing or, on some trims, in the front bumper — both locations get hammered by winter salt and physical damage from car-wash brushes; the bumper-mount harness frays at the grommet where it passes through the bumper backer, and the mirror-mount sensor gets condensation in the connector. 2007-2014 GM full-size trucks (Silverado, Sierra, Tahoe, Yukon, Suburban) mount the AAT in the front bumper near the tow-hook — corrosion at the sensor lead is the most common cause, and GM sells the sensor with a new pigtail because the harness side is usually toast too. 2011-2018 Jeep Grand Cherokee/Dodge Durango and 2006-2010 Dodge Ram mount the AAT behind the grille where it gets bug strikes and the connector fills with debris. 2008-2015 BMW E90/F30 mounts it in the front bumper behind the kidney grille where it overheats from radiator soak and reads high at idle. Estimated repair: $15 (sensor DIY) to $250 (sensor + pigtail + connector replacement at shop).