Rick's Free Auto Repair Advice

P0112 trouble code

P0112- Intake Air Temperature (IAT) Circuit Low Input

A P0112 trouble code indicates that the signal from the intake air temperature sensor signal is less than Self-Test minimum. Depending on the year, make, model and engine, that can mean the IAT sensor is less than the minimum is 0.2 volts or 121°C (250°F).

What sets the P0112 trouble code

Certain conditions must be met before the computer will set the P0112 trouble code, and those conditions vary by car maker. On some GM vehicles, for example, if the PCM detects inlet air temperature above 275°F when the engine has been running at least 10 seconds and thee PCM detects no coolant sensor or VSS sensor trouble codes present, it will set the P0112 trouble code. .

Diagnose and fix P0112 trouble code

A P0112 trouble code can be caused by

• Grounded circuit in harness

• Damaged sensor (backfire, oil contamination, carbon buildup)

• Improper harness connection

• Damaged PCM

How to test an intake air temperature sensor

Intake Air Temperature Sensor

Intake Air Temperature Sensor

Backprobe the wiring at the IAT sensor. Check for a 5-volt reference voltage on one wire and a varying voltage on the other wire depending on the temperature of the air near the IAT sensor. The Intake Air Temperature sensor can be in the intake manifold or in the air duct before the throttle body. The tip of the sensor is exposed to air entering the engine. Some engines have a temperature sensor built into the mass airflow (MAF) sensors to monitor the volume of air entering the engine. Also, some MAP sensors also have an air temperature sensor built into it. And, some engines also have more than one air temperature sensor if the engine has split intake manifolds.

intake air temperature sensor wiring diagram

IAT wiring diagram


The air temperature sensor is a thermistor, so is electrical resistance changes in response to changes in temperature. That, in turn, changes the return voltage to thee PCM. Most air temperature sensors are a negative temperature coefficient (NTC) design where they provide high resistance when they are cold, and resistance drops as they heat up.



However, car makers use a positive temperature coefficient (PTC) IAT that have low resistance when cold, and increase the resistance as the incoming air heats it.

Temperature to Voltage Chart

For a NEGATIVE temperature coefficient (NTC)

Temperature ° F             Voltage              Resistance

50° F                                 3.52 V                58.75Ω

68° F                                 3.06 V                37.30Ω

86° F                                2.62 V                 24.27Ω

104° F                              2.16 V                 16.15Ω

122° F                              1.72 V                 10.97Ω

140° F                              1.35 V                 7.60Ω

158° F                              1.04 V                 5.37Ω

248° F                             0.28 V                 1.18KΩ

©, 2017 Rick Muscoplat


Posted on by Rick Muscoplat


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