P0112 – Intake Air Temperature Sensor 1 Circuit Low

P0112 is an OBD-II trouble code that can make your car run poorly and light up the check engine light, but it’s usually not a mystery once you understand what’s going on. This code points to a problem with the intake air temperature (IAT) sensor circuit reading too low, which the ECU interprets as extremely cold air. That incorrect data can throw off fuel delivery, idle quality, and emissions. In this guide, you’ll learn what P0112 means, common causes, symptoms, how to diagnose it, and the most likely repairs and costs.

What Does P0112 Mean?

P0112 stands for “Intake Air Temperature Sensor 1 Circuit Low Input.” Your engine control unit (ECU) uses the intake air temperature sensor to measure how hot or cold the incoming air is. That information is combined with data from the MAF or MAP sensor to calculate how much fuel to inject.

When you get a P0112 code, the ECU is seeing an abnormally low voltage from the IAT sensor. In most systems, low voltage equals very cold air. If the reading is far outside the expected range, the ECU knows something is wrong with the sensor or wiring and stores P0112.

Quick Reference

  • Code: P0112
  • Definition: Intake Air Temperature Sensor 1 Circuit Low Input
  • System: Engine fuel and air metering
  • Severity: Moderate – can affect drivability and fuel economy
  • Typical causes: Faulty IAT sensor, short to ground, damaged wiring, corroded connector

Real-World Example / Field Notes

In the shop, I see P0112 most often after someone has installed an aftermarket intake or replaced an air filter and accidentally left the IAT connector loose. The car comes in with a check engine light, poor fuel mileage, and sometimes a rough idle. A quick visual check shows the IAT sensor dangling or the harness stretched. Plug it in properly, clear the code, and the problem is gone. Other times, especially on higher-mileage vehicles, the wiring near the airbox gets brittle, cracks, and shorts to ground, causing a permanent “ice-cold” reading on the scan tool.

Symptoms of P0112

  • Check engine light on: The MIL will almost always be illuminated when P0112 is stored.
  • Poor fuel economy: The ECU may enrich the mixture because it thinks the air is very cold and dense.
  • Rough idle or hesitation: Incorrect air temperature data can cause unstable idle and off-idle stumble.
  • Hard starting: Particularly on warm restarts, the engine may crank longer or start roughly.
  • Reduced power: You may notice sluggish acceleration or inconsistent throttle response.
  • Black exhaust smoke: In some cases, an overly rich mixture can cause visible dark smoke from the tailpipe.
  • Failed emissions test: Incorrect fueling can raise HC and CO levels, leading to inspection failure.

Common Causes of P0112

Most Common Causes

  • Faulty IAT sensor: The sensor’s internal thermistor can short internally, sending a constant low-voltage (very cold) signal to the ECU.
  • Short to ground in wiring: Damaged insulation or pinched wires between the IAT sensor and ECU can pull the signal line to ground.
  • Unplugged or loose connector: A partially connected or corroded plug can cause erratic or low readings.
  • Aftermarket intake issues: Incorrectly mounting the IAT sensor in a new intake tube, or leaving it hanging, can lead to wiring stress and failures.

Less Common Causes

  • ECU internal fault: Rare, but a failing engine computer can misinterpret sensor voltage or provide a bad reference.
  • Incorrect sensor installed: Using the wrong sensor type or connector from a different engine family can cause out-of-range signals.
  • Water intrusion or oil contamination: Moisture or oil in the connector or on the sensor tip can alter readings or short the circuit.
  • Harness modifications: Poorly done electrical repairs, splices, or remote-start installations can damage the IAT circuit.

Diagnosis: Step-by-Step Guide

To diagnose P0112 properly, you’ll want a basic scan tool, a digital multimeter (DMM), and ideally a wiring diagram for your specific vehicle. A thermometer or infrared temp gun is also helpful to compare actual air temperature to what the scan tool reports.

  1. Confirm the code and check for others: Scan the ECU for stored and pending codes. Note any related air/fuel or MAF/MAP codes that might point to a broader issue.
  2. View live data: Look at the Intake Air Temperature (IAT) reading on the scan tool with the engine cold. If it shows something unrealistic (like -40°F or -40°C) when it’s clearly warmer, that supports a P0112 fault.
  3. Inspect the sensor and connector: Locate the IAT sensor, usually in the intake tube, airbox, or integrated into the MAF sensor. Check for broken tabs, loose fitment, corrosion, or bent pins at the connector.
  4. Check the wiring harness: Follow the harness a few feet in each direction. Look for rubbed-through insulation, melted sections, or areas where the harness is stretched or pinched.
  5. Test sensor resistance: With the key off and sensor unplugged, measure the resistance across the sensor terminals. Compare to factory specs at ambient temperature. A reading near zero ohms (shorted) is a problem.
  6. Verify reference voltage and ground: Turn the key on, engine off. At the connector, check for the 5V reference (or specified voltage) and a good ground. If reference is missing, you may have a wiring or ECU issue.
  7. Check signal voltage: With the sensor plugged in and key on, back-probe the signal wire. You should see a voltage that changes when the sensor is warmed (for example, by gently heating the intake tube with a hair dryer). A stuck low voltage confirms the issue.
  8. Wiggle test: While watching IAT data on the scan tool, gently move the harness and connector. If the reading jumps around, you likely have an intermittent wiring or connector fault.
  9. Use Mode $06 if available: Some scan tools can access Mode $06 test results to see if the IAT monitor is marginal or intermittently failing before the code sets.
  10. Rule out ECU failure: Only after confirming sensor and wiring integrity should you suspect a bad ECU. This is rare and usually accompanied by multiple unrelated codes.

Pro tip: If your vehicle uses a combined MAF/IAT sensor, don’t automatically replace the whole MAF assembly. Many of these units allow the IAT portion or the connector pigtail to be serviced separately, saving you money.

Possible Fixes & Repair Costs

Most P0112 repairs are straightforward once you pinpoint the fault. Common fixes include replacing the IAT sensor, repairing or replacing damaged wiring, cleaning and securing connectors, or correctly reinstalling the sensor after intake work. In rare cases, ECU repair or replacement is needed.

  • IAT sensor replacement: $20–$80 for the part, plus $50–$120 labor if done at a shop.
  • Connector cleaning/repair: $0–$30 in supplies; $50–$150 labor depending on access and corrosion.
  • Harness repair: $20–$100 in wiring and terminals; $100–$300 labor if sections of harness must be opened and rewrapped.
  • ECU replacement/programming (rare): $400–$1,200+ depending on vehicle and whether a used or reman unit is used.

Overall, typical repair costs for P0112 range from about $100 on the low end (simple sensor swap) to $400–$500 if wiring repairs are involved. Costs vary with vehicle make, labor rates in your area, and how difficult the sensor or harness is to access.

Can I Still Drive With P0112?

In most cases, you can still drive with P0112 without immediate engine damage, but the car may not run well. The ECU often goes into a default strategy for intake air temperature, which can cause rich fueling, poor fuel economy, and rough running, especially during warm starts or heavy acceleration. Short trips to get home or to a repair shop are usually fine, but you shouldn’t ignore the code for weeks. Running rich for a long time can foul spark plugs and overwork the catalytic converter.

What Happens If You Ignore P0112?

If you ignore P0112, the engine may continuously run with incorrect fueling, which can lead to carbon buildup, fouled plugs, contaminated oxygen sensors, and premature catalytic converter failure. You also risk failing emissions inspections and wasting money on fuel. Over time, what started as a simple sensor or wiring issue can turn into a much more expensive repair.

Need wiring diagrams and factory-style repair steps?

Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.

Factory repair manual access for P0112

Check repair manual access

Compare nearby sensor intake trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P2962 – Intake Air Metering Control Valve Position Sensor Circuit Low
  • P0114 – Intake Air Temperature Sensor 1 Circuit Intermittent
  • P0111 – Intake Air Temperature Sensor 1 Circuit Range/Performance
  • P0110 – Intake Air Temperature Sensor 1 Circuit
  • P0113 – Intake Air Temperature Sensor 1 Circuit High
  • P0537 – A/C Evaporator Temperature Sensor Circuit Low

Key Takeaways

  • P0112 means the ECU sees an abnormally low signal from the intake air temperature sensor, indicating a “too cold” reading.
  • Common causes include a bad IAT sensor, shorted wiring, loose connectors, or issues after intake modifications.
  • Symptoms range from a simple check engine light to rough idle, poor fuel economy, and hard starting.
  • Diagnosis involves checking live data, inspecting the sensor and wiring, and verifying voltage and resistance with a multimeter.
  • Most fixes are affordable and straightforward if handled early, typically involving sensor or wiring repairs.

Vehicles Commonly Affected by P0112

P0112 is a generic OBD-II code, so you’ll see it on many makes and models. It’s common on domestic vehicles like Ford, Chevrolet, GMC, Dodge, Chrysler, and Jeep, especially trucks and SUVs with plastic intake tubes that flex and stress the wiring. It also shows up frequently on Honda, Toyota, Nissan, Hyundai, and Kia models, where the IAT is often integrated into the MAF sensor. European brands such as BMW, Volkswagen, Audi, and Mercedes-Benz can set P0112 as well, particularly when aftermarket intakes or engine bay wiring repairs have been done.

FAQ

Can I clear P0112 and keep driving if the car seems fine?

You can clear the code and drive, but if the underlying issue isn’t fixed, P0112 will usually return. The ECU will continue to see incorrect air temperature data, which can slowly cause other problems. It’s best to diagnose and repair the cause rather than repeatedly clearing the code.

Is P0112 caused by a bad mass airflow (MAF) sensor?

Sometimes. On many vehicles, the IAT sensor is built into the MAF housing. In those cases, a failure in the IAT portion can trigger P0112 while the airflow side still seems okay. However, P0112 by itself does not automatically mean the entire MAF is bad; it may just be the IAT circuit or wiring.

Can a dirty air filter cause P0112?

A dirty air filter alone usually does not cause P0112. However, if the airbox or intake tube was opened to replace the filter and the IAT sensor was left unplugged, damaged, or the harness was pulled tight, that can definitely trigger the code. Always double-check connectors after air filter or intake work.

How do I know if my IAT sensor is bad or if it’s a wiring issue?

The best way is to compare resistance and voltage readings to factory specs. If the sensor’s resistance is out of range when unplugged, the sensor is likely bad. If the sensor tests good but the ECU still sees a low signal, you probably have a wiring or connector problem. Visual inspection plus a multimeter test usually tells the story.

Can P0112 cause my car to fail an emissions test?

Yes. The check engine light alone will cause an automatic failure in many areas. Even if your region allows one stored code, the incorrect fueling from bad IAT data can raise emissions enough to fail the tailpipe test. Fixing P0112 before inspection is the safest move.