Your scan tool might show an intake air temperature of nearly 300°F on a cool day. No engine pulls in air that hot, so the engine computer flags the reading. A P0112 code means the intake air temperature sensor signal dropped below its lowest allowed voltage.
This guide explains why a low voltage reads as hot air, what causes it and how to find the fault with a multimeter.
P0112 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 1 | Fuel and air metering | The fault involves the sensors that measure air and fuel. |
| 12 | Specific fault | Intake Air Temperature Circuit Low Input |
What the P0112 Code Means
The SAE J2012 standard defines the P0112 code as Intake Air Temperature Circuit Low Input. “Low input” refers to voltage, not temperature.
The intake air temperature (IAT) sensor is a thermistor. Its resistance drops as air gets hotter. The powertrain control module (PCM) feeds it a 5-volt reference through a resistor, so hot air pulls the signal voltage down. A signal near 0 volts tells the PCM the air is extremely hot, often around 300°F on the scan tool.
A reading that low almost always means the signal wire is shorted to ground or the sensor has shorted inside. The PCM then ignores the sensor and uses a default temperature.
Signs of a Low IAT Signal
A false hot reading makes the PCM think the air is thin. It may cut fuel slightly and pull ignition timing to prevent knock. Watch for these symptoms:
- Check engine light on
- Hard starting when the engine is cold
- Rough idle in cool weather
- Reduced power or sluggish acceleration
- Small drop in fuel economy
Many vehicles show no drivability symptoms at all, since the backup value works well in mild weather.
What Causes the P0112 Code?
Low input faults are almost always electrical. These are the usual causes:
- Signal wire shorted to ground. Chafed insulation lets the wire touch the engine or body.
- Shorted IAT sensor. The thermistor can fail internally and drop to near zero resistance.
- Water in the connector. Moisture can bridge the two pins.
- Damaged MAF sensor. When the IAT sensor is built into the MAF sensor, an internal short sets this code.
- PCM fault. A shorted PCM input is rare.
How to Test the Circuit
You need a digital multimeter, a scan tool with live data and the wiring diagram for your vehicle. The IAT sensor has two wires: a signal wire carrying the 5-volt reference and a sensor ground.
Use the Unplug Test
Turn the key on and watch the IAT reading. Then unplug the sensor. With the sensor unplugged, the scan tool should drop to about -40°F, the lowest value it can show.
If the reading drops to -40°F, the wiring is fine, and the sensor or its MAF housing has shorted. If the reading stays hot with the sensor unplugged, the signal wire is shorted to ground between the connector and the PCM.
Measure the Sensor and Wiring
Measure the sensor’s resistance across its two pins. A reading near 0 ohms confirms an internal short. Many IAT sensors read about 2,000 to 3,500 ohms at 68°F, so check your service manual for the exact chart.
To check the wiring, disconnect the battery and unplug both the sensor and the PCM connector if you can reach it. Measure from the signal wire to engine ground. Any continuity means the wire is shorted and needs repair.
Repairs That Clear the P0112 Code
Fix what your tests found, then clear the code and drive the vehicle. The most common repairs are:
- Repair the shorted wire with solder and heat shrink tubing, and secure it away from sharp edges.
- Dry and clean the connector, then apply dielectric grease to the seal.
- Replace the IAT sensor if it reads near 0 ohms.
- Replace the MAF sensor assembly if the IAT sensor is built in.
Choose an OEM or quality-brand sensor with the correct resistance curve for your engine.
Repair Cost Breakdown
A P0112 code is usually cheap to fix. Here are typical price ranges.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Connector cleaning | $10 to $15 | $50 to $100 |
| Wiring repair | $10 to $30 | $100 to $300 |
| Standalone IAT sensor | $15 to $60 | $75 to $150 |
| MAF sensor with built-in IAT | $80 to $350 | $150 to $500 |
Related Codes Worth Knowing
The P0112 code is part of a family of intake air temperature codes. These related codes help you narrow down the cause:
- P0110: General IAT circuit malfunction
- P0111: IAT reading out of the expected range
- P0113: IAT signal too high, which reads as very cold air
- P0117: Coolant temperature sensor low input, which can point to a shared ground or wiring fault
Fixing a Low IAT Sensor Signal
A P0112 code means the PCM sees a voltage so low that the air would have to be extremely hot. A short to ground or a shorted sensor causes nearly every case.
- Watch the IAT reading with the key on.
- Unplug the sensor and confirm the reading drops to -40°F.
- Measure sensor resistance and check the wire for shorts.
- Replace the sensor only after the wiring tests good.
Frequently Asked Questions
Why Does My Scan Tool Show 300°F for Intake Air?
A reading near 300°F almost always means the signal voltage is close to zero. The PCM converts that low voltage into a very high temperature. Real intake air never gets that hot, so the reading points to a short to ground or a failed sensor, not a cooling problem.
Is It Safe to Drive with a Low IAT Signal?
Short trips are usually safe, since the PCM switches to a default air temperature. Cold starts may be harder, and some engines lose a little power because the PCM pulls timing. Get the circuit tested soon, especially before winter, when hard starting gets worse.
Can Water Cause the P0112 Code?
Water can cause this code when it reaches the IAT connector and bridges the two pins. Driving through deep water, washing the engine bay or a cracked air box can let moisture in. Drying the connector and sealing it with dielectric grease usually fixes the problem if the sensor is not damaged.
Will a New Air Filter Fix the Code?
A new air filter will not fix a low input code, because the fault is electrical. However, the IAT connector is often near the air box. If the code appeared after a filter change, check that the wiring was not pinched when the housing was closed.