P0112: Intake Air Temperature Circuit Low Input

The IAT sensor is reporting a temperature below expected range (very high voltage). May indicate the sensor is reading colder than actual air temperature.

The Intake Air Temperature (IAT) sensor measures the temperature of air entering the engine's intake system. The ECU uses this data to fine-tune fuel injection calculations — cold air is denser (more oxygen per unit volume) and requires more fuel to maintain the correct air-fuel ratio, while warm air is less dense and requires less fuel. The IAT reading also influences ignition timing, as cold air is less prone to detonation, allowing the ECU to run more aggressive timing.

The IAT sensor is an NTC (Negative Temperature Coefficient) thermistor — a simple resistor whose resistance decreases as temperature increases. At room temperature (70°F/21°C), resistance is typically 2,000-3,000 ohms. At engine operating temperature with warm underhood air (200°F/93°C), resistance drops to approximately 200-300 ohms. This resistance change is converted to a voltage signal that the ECU reads through a voltage divider circuit, typically producing 1-4V across the normal temperature range.

Because the IAT sensor is such a simple component, failures are straightforward to diagnose with a basic multimeter. Test the sensor's resistance at known temperatures and compare to manufacturer specifications. The resistance should change smoothly as temperature changes — any sudden jumps or fixed readings indicate a failed sensor.

The IAT sensor is located in one of three places depending on the vehicle: integrated into the Mass Air Flow (MAF) sensor assembly (most common on modern vehicles), mounted separately in the air intake duct between the air filter and throttle body, or threaded into the intake manifold (less common, usually on older vehicles). When the IAT is integrated into the MAF sensor, replacement may require the entire MAF assembly ($80-$300) unless the IAT element can be sourced separately.

Common affected vehicles: virtually any vehicle over 100,000 miles can develop IAT issues, but they're particularly common on Ford vehicles (integrated MAF/IAT assemblies), GM trucks (standalone IAT in the intake duct exposed to temperature extremes), and Honda vehicles (connector corrosion from moisture exposure). The IAT sensor is one of the cheapest repairs in engine management — a standalone sensor costs $10-$40 and takes 10-20 minutes to replace.

**What To Expect at the Shop for P0112:** When you bring your vehicle to a mechanic for P0112, here's what a thorough diagnostic should include: (1) The technician should connect a professional scan tool and read not just the stored code, but also freeze frame data — this shows the exact conditions (RPM, coolant temp, vehicle speed, fuel trims) when the code was set. (2) They should check for related codes that may point to a root cause. (3) A visual inspection of relevant components and wiring should be performed before any parts are replaced. (4) On reputable shops, diagnostic time is typically 0.5-1.0 hours ($50-$150) before any repair work begins. (5) Be wary of shops that want to immediately replace parts based solely on the code number without performing diagnosis — codes indicate symptoms, not specific failed parts.