P1112

P1112 is a Ford-specific code meaning the IAT sensor B circuit is reading intermittent — voltage at the PCM signal pin is jumping in and out of the legal 0.5-4.5 V scaled range (which corresponds to roughly -40 F at 4.5 V down to 248 F at 0.5 V on a standard NTC thermistor) instead of moving smoothly with airflow. Cheapest-first ladder: (1) Scan-tool live data — watch IAT B with the key on and tap/wiggle the sensor connector and the harness from the sensor back to the PCM; a value that jumps 30+ degrees on wiggle is harness/connector, a value that reads steady but wrong is the sensor itself. (2) Back-probe the signal wire and ohm the sensor — Ford IAT spec is roughly 95-100 kohms at -40 F, 35-40 kohms at 32 F, 2-3 kohms at 176 F, 0.7-1.0 kohm at 248 F; out-of-curve readings condemn the sensor for ~$25. (3) Check connector pins for green/white corrosion (especially on intercooler-mounted IAT B sensors on EcoBoost trucks that see road-spray) — DeoxIT and a re-pin often clears the code permanently. Don't replace the PCM or the entire intake manifold harness before reading the keep-alive memory for prior tune flashes — aftermarket tunes (SCT, Livernois, Bully Dog) sometimes rescale the IAT B input for boost-cooler kits and leave the diagnostic threshold wrong, which is a software fix, not a parts fix.

Vehicle-specific patterns: 2011-2018 Ford F-150 EcoBoost 3.5L / 2.7L commonly throws P1112 from the intercooler-outlet IAT B sensor (the second IAT used to compute charge-air temp post-intercooler) — condensation pools in the connector after washing and the sensor reads erratically; this is the single most common P1112 in modern Ford shop work. 2015-2020 Ford Mustang EcoBoost 2.3L throws P1112 from a known harness routing where the IAT B pigtail crosses the turbo heat shield. 2008-2010 Ford F-250/F-350 6.4L Powerstroke diesel throws P1112 from EGR-cooler crud blocking the IAT B sensor face, giving artificially slow response — clean the sensor tip before replacing. 1997-2003 Ford F-150 / Crown Vic 4.6L Triton with the older two-sensor IAT setup will throw P1112 from a brittle connector lock that intermittently loses contact with engine vibration. Estimated repair: $40 (clean connector, dielectric grease) to $280 (OEM IAT B sensor + pigtail repair on EcoBoost intercooler).