Circuit Description
The intake air temperature (IAT) sensor is a variable resistor that measures the temperature of the air entering the engine. The IAT sensor has a signal circuit and a low reference circuit. The engine control module (ECM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. If the ECM detects an intermittent low IAT signal voltage, which is a high temperature indication, this DTC sets.
The following table illustrates the difference between temperature, resistance, and voltage:
IAT | IAT Resistance | IAT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
DTC Descriptor
This diagnostic supports the following DTC:
DTC P1112 Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage
Conditions for Running the DTC
| • | DTC P0502 is not set. |
| • | The vehicle speed is more than 50 km/h (31 mph). |
| • | The engine run time is more than 120 seconds. |
| • | This DTC runs continuously when the above conditions are met. |
Conditions for Setting the DTC
| • | The ECM detects that the IAT is more than 149°C (300°F) intermittently. |
| • | The condition exists for more than 20 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. |
Diagnostic Aids
Check for the following conditions:
| • | Test the engine coolant temperature (ECT) sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition. |
| • | If the vehicle has set overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F). Refer to Temperature Versus Resistance . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |
2 | Observe the DTC Information with a scan tool. Is DTC P0112 set? | Go to DTC P0112 | Go to Step 3 |
3 | Observe the intake air temperature (IAT) sensor parameter with a scan tool while moving the IAT sensor connector and the engine control module (ECM) connector. Refer to Inducing Intermittent Fault Conditions in Wiring Systems. Does the scan tool indicate an abrupt change in value? | Go to Step 5 | Go to Step 4 |
4 | Observe the IAT sensor parameter with a scan tool while moving the wiring harness between the IAT sensor and the ECM. Refer to Inducing Intermittent Fault Conditions in Wiring Systems. Does the scan tool indicate an abrupt change in value? | Go to Step 6 | Go to Diagnostic Aids |
5 | Repair the connector/terminal as necessary. Refer to Connector Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | -- |
6 | Repair the harness/wiring as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | -- |
7 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 8 |
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
