Circuit Description
The intake air temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit. If the ECM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P1112 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1112 Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage.
Conditions for Running the DTC
| • | DTCs P0117, P0118, P0502, P0503 are not set. |
| • | The engine run time is more than 10 seconds. |
| • | The vehicle speed sensor (VSS) indicates that vehicle speed is more than 40 km/h (25 mph). |
| • | The engine coolant temperature (ECT) is less than 110°C (230°F). |
| • | This DTC runs continuously within the enabling conditions. |
Conditions for Setting the DTC
The ECM detects that the IAT sensor parameter is more than 149°C (300°F) intermittently for more than 5 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Observe the intake air temperature (IAT) sensor parameter with a scan tool. Is the IAT sensor parameter more than the specified value? | 149°C (300°F) | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections |
4 |
Is the IAT sensor parameter less than the specified value? | -39°C (-38°F) | Go to Step 6 | Go to Step 5 |
5 | Test the signal circuit of the IAT sensor for an intermittent short to ground or an intermittent short to the IAT low reference circuit. Refer to Circuit Testing , Inducing Intermittent Fault Conditions , and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 |
6 | Test for an intermittent and for a poor connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections , Inducing Intermittent Fault Conditions , and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
7 | Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections , Inducing Intermittent Fault Conditions , and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
8 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 |
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
