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
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.
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