Your check engine light is on, and the scan tool points to the intake air temperature sensor. The engine may still run fine, or it may start hard and idle rough. A stored P0110 code means the engine computer found a problem in the intake air temperature (IAT) sensor circuit.
This guide explains how the sensor works, what breaks the circuit and how to test it with a basic multimeter.
P0110 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. |
| 10 | Specific fault | Intake Air Temperature Circuit Malfunction |
What Does the P0110 Code Mean?
The SAE J2012 standard defines the P0110 code as Intake Air Temperature Circuit Malfunction. The PCM found an electrical problem in the IAT circuit that does not fit a simple high or low reading.
The IAT sensor is a thermistor, a resistor that changes value with temperature. Cold air gives high resistance, and hot air gives low resistance. The powertrain control module (PCM) sends the sensor a 5-volt reference through a resistor and reads the voltage that comes back. A cold sensor returns a high voltage, and a hot sensor returns a low one.
Many modern engines build the IAT sensor into the mass air flow (MAF) sensor. Others mount it in the air filter box or intake tube. The PCM uses the reading to fine-tune fuel delivery and ignition timing, since cold air is denser than hot air.
Common Symptoms of an IAT Circuit Fault
When the reading fails, the PCM usually swaps in a default temperature. Many drivers notice only the warning light. Watch for these signs:
- Check engine light on
- Hard starting, especially in very cold or very hot weather
- Rough idle
- Hesitation on acceleration
- Slightly worse fuel economy
- Engine knock or pinging under load on some engines
What Causes the P0110 Code?
The IAT circuit is simple, so most faults are easy to find. Wiring and connectors fail more often than the sensor. These are the usual causes:
- Loose or unplugged connector. The connector often gets bumped during air filter service.
- Corroded or bent pins. Moisture in the air box can corrode the terminals.
- Damaged wiring. Wires can chafe, break or get chewed by rodents.
- Failed IAT sensor. The thermistor can crack or drift with age.
- Failed MAF sensor. When the IAT sensor sits inside the MAF sensor, the whole unit is replaced.
- PCM fault. A failed PCM input is rare, so rule out everything else first.
How to Diagnose the P0110 Code Step by Step
You need a scan tool with live data, a digital multimeter and a wiring diagram for your vehicle. The diagram shows which pins carry the reference and ground.
Compare IAT with Outside Temperature
Let the car sit overnight so the engine cools fully. Turn the key on without starting the engine and read the IAT and engine coolant temperature (ECT) on the scan tool. Both should be within about 5 to 10°F of the outside air temperature.
A reading stuck at about -40°F usually means an open circuit. A reading near 300°F usually means a short to ground. A reading that jumps around points to a loose connection.
Test the Wiring and Sensor
Unplug the sensor and turn the key on. The reference wire should read close to 5 volts, and the ground should read close to 0 volts against the battery negative post. With the sensor unplugged, the scan tool should show about -40°F.
Next, connect a fused jumper wire between the two connector pins. The scan tool reading should jump to a very high temperature. If it does, the wiring and PCM are good, and the sensor is the likely cause. You can also measure the sensor’s resistance. Many IAT sensors read about 2,000 to 3,500 ohms at 68°F, but check your service manual for the exact chart.
How to Fix the P0110 Code
Match the repair to what your tests found. Then clear the code and drive the vehicle through a full warm-up.
- Connector problems: Reseat the connector, clean corroded pins with electrical contact cleaner or replace the pigtail.
- Wiring damage: Repair broken wires with solder and heat shrink tubing.
- Failed sensor: Replace the IAT sensor. Most standalone sensors twist or snap out of the intake tube in minutes.
- Integrated sensor: Replace the MAF sensor assembly if the IAT sensor is built into it.
Buy an OEM or quality-brand part. A sensor with the wrong resistance curve can set new temperature codes.
Repair Costs at a Glance
IAT repairs are among the cheapest engine sensor fixes. This table shows typical price ranges.
| Repair | DIY Parts Cost | Typical Shop Cost |
|---|---|---|
| Clean connector and pins | $10 to $15 | $50 to $100 |
| Replace connector pigtail | $15 to $40 | $100 to $200 |
| Replace standalone IAT sensor | $15 to $60 | $75 to $150 |
| Replace MAF sensor with built-in IAT | $80 to $350 | $150 to $500 |
Is It Safe to Drive with a P0110 Code?
You can usually keep driving for a short time. The PCM uses a default air temperature, so most engines run close to normal.
The default value can still cause hard starts in extreme weather and a small loss in fuel economy. Some engines also pull ignition timing to protect against knock. Plan the repair within a week or two, and your car will fail an OBD-II emissions test until it is fixed.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0111 | Intake Air Temperature Circuit Range/Performance Problem |
| P0112 | Intake Air Temperature Circuit Low Input |
| P0113 | Intake Air Temperature Circuit High Input |
| P0114 | Intake Air Temperature Circuit Intermittent |
| P0115 | Engine Coolant Temperature Circuit Malfunction |
Fixing an Intake Air Temperature Circuit Fault for Good
A P0110 code means the PCM cannot trust the intake air temperature signal. Connectors and wiring cause most cases, so test them before you replace the sensor.
- Compare IAT, ECT and outside temperature after a cold soak.
- Check the 5-volt reference and ground.
- Use the unplug and jumper tests to split wiring from sensor faults.
- Replace the sensor, or the MAF sensor if it is built in, only after the wiring tests good.
Frequently Asked Questions
Where Is the IAT Sensor Located?
On many newer vehicles, the IAT sensor is built into the mass air flow sensor in the intake tube. On others, it sits in the air filter housing, the intake tube or the intake manifold. Some turbocharged engines have a second air temperature sensor after the intercooler. Your service manual shows the exact location.
Can a Bad IAT Sensor Cause Poor Gas Mileage?
A failed IAT sensor can cause a small drop in fuel economy. The PCM may add extra fuel if it thinks the air is colder than it really is. The effect is usually minor compared with a bad MAF or oxygen sensor, but it adds up over thousands of miles.
Will a Cold Air Intake Set the P0110 Code?
A cold air intake does not set this circuit code by itself. However, installing one often means unplugging and moving the IAT sensor. A connector left loose or a wire stretched too tight can then trigger the code. Check the connector and wire routing first if the code appeared after an install.
Can I Clean an IAT Sensor?
You can gently clean an IAT sensor with MAF sensor cleaner if oil or dirt coats the tip. Cleaning rarely fixes a circuit code, though, because the fault is usually electrical. Let the sensor dry fully before you reinstall it, and never scrape the thermistor element.