Circuit Description
The DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage diagnostic detects an out of range sensor signal. The IAT sensor is a thermistor that is an integral part of the mass air flow (MAF) sensor. The electrical resistance of the IAT sensor is high when the air temperature is cold, and the resistance is low when the air temperature is warm. The IAT sensor is wired in series with a fixed resistor located in the powertrain control module (PCM). The PCM applies 5 volts to the IAT sensor. The PCM monitors the voltage across the IAT sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the air temperature is cold, and low when the air temperature is warm.
Temperature | IAT Resistance | IAT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0112 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
The temperature input is more than 140°C (284°F), 0.18 volts, for at least 0.5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM enters the Fail Safe Function in which the intake air temperature will default to 20°C (68°F). |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function. |
Diagnostic Aids
Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted IAT sensor. A shifted sensor could result in a DTC P0112. Refer to Temperature Versus Resistance .
An intermittent malfunction may be caused by a fault in the IAT sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0112 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step checks for a low voltage on the input circuit. If the scan tool reads 140°C (284°F), the input circuit is shorted to ground.
-
This step determines if DTC P0112 is the result of a hard failure or an intermittent condition.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |
Select the IAT sensor parameter on the scan tool. Is the IAT sensor value more than or equal to the specified value? | 140°C (284°F) | Go to Step 4 | Go to Step 3 | |
Does the DTC run and pass? | -- | Go to Diagnostic Aids | Go to Step 4 | |
4 |
Is the IAT sensor value equal to the specified value? | -40°C (-40°F) | Go to Step 6 | Go to Step 5 |
5 |
Did you find and correct a condition? | -- | Go to Step 8 | Go to Step 7 |
6 | Replace the MAF sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
7 | Replace the powertrain control module (PCM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Does the DTC run and pass? | -- | Go to Step 9 | Go to Step 2 |
9 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
