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P0112 Code Explained: Intake Air Temperature (IAT) Sensor 1 Circuit Low Input Causes, Symptoms & Fixes

P0112 Code Explained illustration showing an Intake Air Temperature sensor with a short-to-ground fault, extremely high temperature reading, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com branding.

If your OBD-II scanner displays P0112, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an abnormally low-voltage signal from the Intake Air Temperature (IAT) Sensor 1 circuit.

The generic OBD-II definition for P0112 is:

Intake Air Temperature Sensor 1 Circuit Low Input

Despite the words “low input,” P0112 usually does not mean the intake-air temperature is too low. It means the electrical voltage in the sensor circuit is below the PCM’s expected range.

Because most Intake Air Temperature sensors use a negative temperature coefficient thermistor, low signal voltage is interpreted as an extremely high intake-air temperature.

Depending on the vehicle, the scan tool may display an impossible reading such as:

The sensor may actually be shorted internally, the signal wire may be shorted to ground, or the connector may be contaminated with moisture or conductive debris.

Replacing the sensor without testing the circuit can turn a simple wiring repair into another episode of “parts cannon diagnostics,” where perfectly good components are replaced until the owner’s wallet develops its own warning light.

Alternate Manufacturer Definitions

Depending on the manufacturer, scan tool, or service information, P0112 may appear as:

Although the wording differs, the underlying problem is similar: the PCM sees less voltage than expected on the Intake Air Temperature Sensor 1 signal circuit.

P0112 Quick Facts

ItemInformation
Diagnostic codeP0112
Generic definitionIntake Air Temperature Sensor 1 Circuit Low Input
SystemEngine air intake and fuel management
Fault categoryElectrical circuit low
Sensor typeNegative temperature coefficient thermistor
Typical scan readingExtremely high intake temperature
SeverityLow to moderate
Safe to drive?Usually for a limited time
Most common causesShorted sensor, signal wire shorted to ground, damaged connector
Typical repair cost$50–$600+

What Does the P0112 Code Mean?

The PCM supplies or monitors voltage through the Intake Air Temperature sensor circuit.

The IAT sensor changes resistance according to incoming-air temperature. The PCM then converts that voltage signal into a temperature value.

On most vehicles:

When the signal voltage falls below the calibrated threshold for a specific amount of time, the PCM stores P0112.

The PCM may interpret this low voltage as an extremely hot intake-air condition, even when the actual air entering the engine is cool.

Does “Circuit Low” Mean the Air Is Too Cold?

No.

This is one of the most common misunderstandings surrounding P0112.

“Circuit low” refers to low electrical signal voltage, not low air temperature.

Because of how an NTC thermistor works, the relationship is effectively reversed:

Circuit conditionPCM interpretation
High resistanceCold intake air
High signal voltageCold intake air
Low resistanceHot intake air
Low signal voltageHot intake air

Therefore, P0112 commonly causes the scan tool to show an intake-air temperature that is unrealistically hot.

What Is the Intake Air Temperature Sensor?

The Intake Air Temperature sensor measures the temperature of air entering the engine.

The PCM uses this information to estimate air density and adjust:

Cold air is denser and contains more oxygen than warm air. Accurate temperature data helps the PCM determine how much fuel the engine needs.

How Does the IAT Sensor Work?

Most IAT sensors use a negative temperature coefficient thermistor.

A thermistor is a resistor whose resistance changes with temperature.

For an NTC thermistor:

The PCM typically monitors the sensor using a reference or pull-up voltage and a sensor-ground circuit.

A simplified example may look like this:

Intake-air temperatureApproximate resistanceApproximate signal voltage
32°FHigh3.5–4.5 volts
68°FModerate2.0–3.5 volts
104°FLower1.0–2.0 volts
176°FVery lowBelow 1 volt

Exact resistance and voltage values vary significantly by manufacturer.

Always consult the correct service information before judging a sensor by generic specifications.

What Does Sensor 1 Mean?

“Sensor 1” identifies the primary Intake Air Temperature sensor used by the PCM.

The sensor may measure air temperature:

Some engines use multiple air-temperature sensors.

For example, a turbocharged engine may include:

Do not assume the code refers to the first temperature sensor you happen to find under the hood.

Where Is the IAT Sensor Located?

The sensor location depends on the engine and airflow-measurement strategy.

Common locations include:

On many vehicles, the IAT sensor is integrated into the MAF sensor.

If the thermistor fails internally, the entire MAF/IAT assembly may require replacement unless the manufacturer services the sensor separately.

How the PCM Detects P0112

The PCM continuously monitors IAT signal voltage.

P0112 may be stored when:

The fault usually must remain present for a calibrated period before the code sets.

Some vehicles may store P0112 immediately, while others require:

Typical Voltage Conditions for P0112

The exact trigger voltage varies by vehicle, but P0112 often sets when the IAT signal drops near the bottom of its expected range.

A typical circuit may operate between approximately:

The PCM may set P0112 when voltage remains below approximately:

These are only general examples.

Manufacturer-specific diagnostic charts must take priority.

What Temperature Does P0112 Usually Display?

A vehicle with P0112 may display an intake-air temperature near the PCM’s maximum programmed value.

Possible readings include:

The exact number is not universal.

The important clue is that the reported temperature is far higher than actual intake-air temperature, especially before the engine has been started.

For example:

SensorCold-engine reading
Ambient temperature65°F
Coolant temperature67°F
Intake Air Temperature284°F

Unless the vehicle was parked inside an industrial oven, the IAT reading is clearly incorrect.

P0112 Compared With P0110 Through P0114

CodeDefinitionTypical issue
P0110IAT Sensor 1 Circuit MalfunctionGeneral electrical fault
P0111IAT Sensor 1 Range/PerformanceImplausible or sluggish reading
P0112IAT Sensor 1 Circuit Low InputSignal voltage too low
P0113IAT Sensor 1 Circuit High InputSignal voltage too high
P0114IAT Sensor 1 Circuit IntermittentSignal drops in and out

A simple way to remember the difference:

P0112 vs P0113

P0112 and P0113 represent opposite electrical conditions.

P0112

P0113

This distinction is useful during diagnosis because the live-data temperature often reveals which electrical direction the circuit has failed.

Common Symptoms of P0112

Symptoms vary depending on the vehicle, climate, and PCM fallback strategy.

Common symptoms include:

Some vehicles may show no noticeable drivability symptoms because the PCM substitutes a default temperature value.

Check Engine Light

The most common symptom is an illuminated Check Engine Light.

P0112 may appear as:

The warning light may remain on even if the circuit temporarily returns to normal.

Extremely High Intake-Air Temperature Reading

The clearest diagnostic clue is often an implausibly high IAT reading on the scan tool.

A reading above 200°F on a cold engine strongly suggests:

Always compare IAT with actual ambient temperature and coolant temperature after a full cold soak.

Hard Starting

The PCM uses intake temperature to calculate cold-start fueling.

If it believes the incoming air is extremely hot, it may reduce enrichment during startup.

This can cause:

The problem may be more noticeable in cold climates.

Rough Idle

Incorrect air-density calculations can affect fuel delivery and spark timing.

The engine may:

A rough idle alone does not prove the IAT sensor is responsible, but it supports the diagnosis when combined with an unrealistic temperature reading.

Poor Acceleration

The PCM may alter timing and fuel delivery because it believes intake air is excessively hot.

Drivers may notice:

The vehicle may feel normal during light driving but weak under load.

Poor Fuel Economy

An inaccurate IAT signal can disrupt:

Depending on the PCM strategy, the engine may operate richer or leaner than intended.

Either condition can reduce fuel economy.

Rich or Lean Operation

Although a low-voltage IAT signal represents hot air, the PCM’s response varies.

Some vehicles may reduce fuel delivery because warm air is less dense.

Others may apply substitute values or protective strategies that result in richer operation.

The final fuel mixture depends on:

This is why fuel-trim data should be reviewed during diagnosis.

Can P0112 Cause Misfires?

Yes, although misfires are not the most common symptom.

Incorrect temperature data may contribute to:

Look for companion codes such as:

Do not assume P0112 is the only cause of the misfire without completing a full diagnosis.

Can P0112 Affect Turbocharged Engines?

Yes.

Turbocharged engines rely heavily on intake-temperature data for:

If the PCM believes intake air is dangerously hot, it may:

The result may feel like a major turbocharger problem even though the actual fault is a shorted temperature-sensor circuit.

Can P0112 Affect Transmission Operation?

Indirectly, yes.

Modern automatic transmissions often depend on PCM-calculated engine torque.

Incorrect IAT data may change:

Possible symptoms include:

These symptoms are usually secondary to the engine-management fault.

Is P0112 Serious?

P0112 is generally considered a low-to-moderate severity code.

The engine will often continue running because the PCM substitutes a default temperature value.

However, the fault should not be ignored because it may affect:

Severity increases if the vehicle also has:

Can You Drive With P0112?

You can usually drive a short distance with P0112 if:

Avoid continued driving if:

A circuit fault that seems minor can become expensive if incorrect fueling damages the catalytic converter.

Can a Dirty IAT Sensor Cause P0112?

Usually not by itself.

Contamination commonly causes:

P0112 more strongly suggests an electrical low-voltage condition.

However, conductive contamination involving moisture, oil, metallic debris, or corrosion may create a path to ground and pull the signal voltage low.

Can a Dirty Air Filter Cause P0112?

A dirty air filter is unlikely to directly cause P0112.

A clogged filter may affect airflow and engine performance, but it normally does not pull the IAT circuit voltage below its electrical threshold.

Check the air filter during diagnosis, but do not expect a new filter to repair a shorted signal circuit.

Can an Aftermarket Intake Cause P0112?

Yes.

Aftermarket intake installation may cause P0112 through:

The intake pipe itself does not generate the code. The installation and wiring problems around it often do.

Can a Weak Battery Cause P0112?

A weak battery is not a common direct cause.

However, unstable voltage may contribute to:

If P0112 appears with several unrelated electrical codes, test:

Can a Vacuum Leak Cause P0112?

A vacuum leak usually does not directly cause an IAT circuit-low code.

Vacuum leaks more commonly trigger:

However, intake work that creates a vacuum leak may also damage or disconnect IAT wiring.

Treat the timing of recent repairs as an important clue.

25 Common Causes of P0112

The most common causes include:

  1. Internally shorted IAT sensor
  2. IAT signal wire shorted to ground
  3. Damaged sensor connector
  4. Moisture inside the connector
  5. Corroded connector terminals
  6. Conductive debris bridging terminals
  7. Pinched intake-harness wiring
  8. Melted wiring insulation
  9. Harness chafing against metal
  10. Incorrect previous wiring repair
  11. Reversed connector terminals
  12. Shorted integrated MAF/IAT sensor
  13. Failed combined MAP/IAT sensor
  14. Failed TMAP sensor
  15. Damaged aftermarket extension harness
  16. Improperly installed cold-air intake
  17. Sensor contaminated with conductive material
  18. Poor sensor-ground circuit configuration
  19. Short between the signal and ground wires
  20. Water intrusion from engine cleaning
  21. Rodent-damaged wiring
  22. PCM connector corrosion
  23. PCM connector terminal damage
  24. PCM software or calibration issue
  25. Failed PCM input circuit

1. Internally Shorted IAT Sensor

An internally shorted thermistor is one of the most common causes of P0112.

When resistance becomes too low, signal voltage drops and the PCM interprets the reading as extremely hot intake air.

The sensor may fail because of:

Resistance testing can usually confirm the failure.

2. Signal Wire Shorted to Ground

The IAT signal wire may contact:

This pulls the signal voltage low and may produce a fixed maximum-temperature reading.

Inspect the harness near:

3. Damaged Sensor Connector

A broken or distorted connector may allow the signal and ground terminals to contact each other.

Inspect for:

Connector damage is especially common after repeated air-filter or intake service.

4. Moisture and Corrosion

Water intrusion can create a conductive path between connector terminals.

Possible sources include:

Green or white corrosion indicates that moisture has been present long enough to damage terminal surfaces.

5. Integrated MAF/IAT Sensor Failure

Many vehicles combine the IAT sensor with the Mass Air Flow sensor.

The MAF portion may continue working while the IAT thermistor fails.

This means a vehicle can have:

Test the temperature circuit independently before replacing the full MAF assembly.

6. Aftermarket Intake Wiring Problems

Cold-air and short-ram intake installations often require the sensor connector to be moved.

Problems may include:

Inspect any modification performed shortly before the code appeared.

7. Melted Wiring

Turbochargers, exhaust manifolds, and EGR components generate enough heat to damage nearby wiring.

Melted insulation may allow the signal conductor to contact ground.

Heat damage may be hidden beneath:

Do not stop the inspection just because the outside of the harness looks acceptable.

8. Incorrect Previous Repair

Previous repairs may introduce:

A repair can look neat and still be electrically wrong.

Verify wire colors and terminal positions using the correct wiring diagram.

9. Rodent Damage

Rodents frequently damage wiring near:

Partially chewed wiring may allow conductors to contact grounded components.

Look for:

10. PCM Failure

A failed PCM input circuit is possible but uncommon.

Before replacing the PCM, verify:

The PCM should be the final suspect, not the opening act.

Unlike P0111, which indicates an implausible or slow sensor reading, P0112 is usually an electrical fault. The PCM is seeing signal voltage that is lower than expected, which it interprets as extremely hot intake air.

The most common causes include a shorted IAT sensor, signal wire shorted to ground, connector corrosion, moisture intrusion, damaged wiring, or a failed integrated MAF/IAT sensor.

Proper diagnosis means confirming the low-voltage condition before replacing parts.

How to Diagnose the P0112 Code

Step 1: Confirm the Code

Connect a professional OBD-II scan tool and record:

Do not clear the code until all diagnostic information has been saved.

The freeze-frame data may reveal whether the fault occurred:

Step 2: Check for Related Codes

Inspect for additional codes involving:

Frequently associated codes include:

Several temperature-related codes may indicate a shared wiring or ground problem.

Step 3: Compare Cold-Soak Temperatures

Allow the engine to sit overnight whenever possible.

Before starting the engine compare:

These readings should normally be very close.

Example:

That IAT reading clearly indicates a fault.

Cold-soak comparison remains one of the quickest diagnostic tests for P0112.

Step 4: Review Live Data

Monitor the Intake Air Temperature value.

Watch for:

If the sensor reports maximum temperature continuously, suspect:

Step 5: Perform a Visual Inspection

Inspect the complete intake system.

Look for:

Many P0112 faults are discovered before a multimeter is ever connected.

Step 6: Identify the Sensor Type

Determine whether the vehicle uses:

This determines:

Always verify the sensor configuration before ordering parts.

Step 7: Inspect the Connector

Disconnect the sensor.

Inspect for:

Corrosion increases electrical problems and may pull the signal toward ground.

Step 8: Verify Terminal Tension

Using the proper terminal tester, verify the connector grips firmly.

Loose terminals can create:

Avoid using oversized probes that permanently spread connector terminals.

Step 9: Check for Moisture

Inspect for evidence of:

Dry the connector completely before further testing.

Repair damaged seals if moisture is found.

Step 10: Check Live Data While Moving the Harness

Observe Intake Air Temperature while gently moving:

Temperature changes during movement often indicate wiring damage.

Step 11: Disconnect the Sensor

Unplug the sensor.

Many vehicles immediately display an extremely cold reading.

If the scan tool changes from:

280°F → -40°F

the PCM is reacting correctly.

This suggests:

Results vary by manufacturer.

Step 12: Measure Sensor Resistance

Disconnect the sensor.

Measure resistance across the terminals.

Compare resistance with:

Most NTC sensors should show:

A near-zero resistance reading usually indicates a failed sensor.

Step 13: Warm the Sensor

Apply gentle heat.

Watch resistance decrease smoothly.

Sudden drops or fixed resistance indicate sensor failure.

Never use an open flame.

Unlike marshmallows, thermistors do not improve when roasted.

Step 14: Check Signal Voltage

Backprobe the connector.

Measure signal voltage with:

If voltage remains near zero:

Inspect for:

Always compare with factory specifications.

Step 15: Test for a Short to Ground

Disconnect both sensor and PCM where required.

Check continuity between:

Continuity where none should exist indicates:

Step 16: Check Wiring Continuity

Measure continuity between:

Inspect for:

Good continuity alone does not prove the circuit is healthy.

Voltage-drop testing is equally important.

Step 17: Verify Sensor Ground

Inspect the sensor ground.

Perform:

Poor grounds may create misleading voltage readings.

Step 18: Inspect MAF/IAT Assembly

If the IAT sensor is integrated into the MAF:

Inspect:

A healthy MAF airflow reading does not automatically mean the IAT portion is functioning correctly.

Step 19: Inspect Aftermarket Modifications

Check for:

Many P0112 codes appear shortly after intake installation.

Step 20: Inspect Heat Damage

Check harness routing near:

High temperatures frequently melt insulation.

Step 21: Inspect PCM Connector

Inspect PCM connectors for:

Follow manufacturer procedures before disconnecting the PCM.

Step 22: Verify Battery Voltage

Measure:

Typical charging voltage:

13.5–14.8 volts

Multiple electrical faults should prompt charging-system testing.

Step 23: Check Technical Service Bulletins

Search manufacturer bulletins covering:

A factory bulletin may eliminate unnecessary repairs.

Step 24: Verify PCM Operation

Only after confirming:

should PCM diagnosis begin.

PCM failures remain uncommon.

Step 25: Verify the Repair

After repairs:

  1. Clear all DTCs.
  2. Cold-soak the vehicle if possible.
  3. Compare IAT, ECT and ambient temperatures.
  4. Road test.
  5. Monitor live data.
  6. Complete drive cycle.
  7. Recheck pending codes.
  8. Confirm P0112 does not return.

Never consider the repair complete until live data behaves normally.

Common Repairs for P0112

Typical repairs include:

P0112 Repair Costs

RepairEstimated Cost
Diagnostic testing$100–$200
Connector cleaning$20–$100
Wiring repair$100–$500
Separate IAT sensor$80–$250
MAF/IAT assembly$150–$650
Intake harness repair$150–$600
Ground repair$100–$300
PCM software update$100–$300
PCM replacement/programming$1,000–$3,500+

A five-dollar corroded connector can imitate a six-hundred-dollar sensor. Testing first is always cheaper than guessing.

Common Diagnostic Mistakes

Replacing the Sensor Immediately

Always verify:

before replacing the sensor.

Ignoring Cold-Soak Comparison

This quick test often identifies the fault within minutes.

Skipping it wastes valuable diagnostic time.

Assuming the MAF Sensor Is Bad

An integrated sensor may require MAF replacement.

However, confirm the IAT circuit first.

Ignoring Moisture

Water intrusion commonly creates low-voltage faults.

Inspect connector seals carefully.

Overlooking Heat Damage

Harnesses routed near turbochargers and exhaust manifolds frequently develop insulation failures.

Using Incorrect Replacement Sensors

Poor-quality aftermarket thermistors may have incorrect resistance values.

Use quality OEM or premium replacement parts.

Replacing the PCM First

PCM failures are rare.

Complete every electrical test before condemning the control module.

Manufacturer-Specific Notes

General Motors

Inspect:

Ford

Check:

Toyota / Lexus

Compare:

before startup.

Honda / Acura

Inspect:

Nissan / Infiniti

Check:

Hyundai / Kia

Inspect:

Volkswagen / Audi

Verify whether the code applies to:

BMW / MINI

Inspect:

Mercedes-Benz

Inspect:

Subaru

Inspect:

Chrysler, Dodge, Jeep and Ram

Inspect:

Preventative Maintenance

To reduce future P0112 faults:

Five extra minutes routing a wiring harness properly can prevent hours of electrical diagnosis later.

Frequently Asked Questions

What does P0112 mean?

The PCM has detected an Intake Air Temperature Sensor 1 signal voltage that is lower than expected.

Does P0112 mean the sensor is bad?

Not always.

Possible causes include:

What scan-tool reading usually accompanies P0112?

An unrealistically high intake-air temperature.

Can I drive with P0112?

Usually for a short period if the engine runs normally.

Avoid driving if:

occur.

Can a bad MAF cause P0112?

Yes.

If the IAT sensor is integrated into the MAF housing, internal failure can trigger P0112.

Can moisture cause P0112?

Yes.

Moisture may short the signal to ground.

Can a cold-air intake cause P0112?

Yes.

Improper wiring or connector damage during installation is common.

Can P0112 reduce turbo boost?

Yes.

Many turbocharged engines reduce boost when intake-temperature data is implausible.

How much does P0112 cost to repair?

Repairs range from less than $100 for connector service to $650 for an integrated MAF/IAT assembly. PCM replacement is uncommon but can exceed $3,500.

What is the difference between P0111 and P0112?

P0111 indicates an implausible or slow sensor reading.

P0112 indicates the sensor signal voltage is electrically too low.

Final Thoughts

The P0112 Intake Air Temperature Sensor 1 Circuit Low Input code indicates that the PCM has detected an abnormally low electrical signal from the primary Intake Air Temperature sensor.

The most common causes include:

The best diagnostic approach begins with a cold-soak comparison, followed by live-data analysis, resistance testing, voltage checks, connector inspection, and wiring verification before replacing any components.

Replacing the PCM should remain the last step after every other electrical possibility has been eliminated.

Related Pro Street Diagnostic Guides

Intake Air Temperature Sensor 1 Codes

Intake Air Temperature Sensor 2 Codes

Related Air-Metering Codes

Complete OBD-II Code Libraries

For the strongest topical authority, interlink this article with P0110–P0114, the P0095–P0099 Intake Air Temperature Sensor 2 series, and the P0100–P0109 Mass Air Flow and MAP sensor guides.

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