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 excessively 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 procedure supports the following DTC:
DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | DTC P0502 is not set. |
| • | The engine run time is more than 120 seconds. |
| • | The vehicle speed is more than 50 km/h (31 mph). |
| • | DTC P0112 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the IAT sensor is more than 149°C (300°F) for more than 10 seconds.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame/Failure Records buffers. |
| • | A history DTC is stored. |
| • | The ECM will substitute a default value for intake air temperature. The scan tool will not show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
| • | Test the IAT 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 engine has sat overnight, the IAT sensor and the engine coolant temperature (ECT) sensor values should display within 3°C (5°F). Refer to Temperature Versus Resistance . |
| • | A high resistance on either the IAT sensor signal circuit or the IAT sensor low reference circuit may not set a DTC. Refer to Circuit Testing in Wiring Systems. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Step | Action | Values | 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 |
Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool. Is the temperature more than the specified value? | 130°C (266°F) | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the voltage less than the specified value? | 4.8 V | Go to Step 5 | Go to Step 6 |
5 | Test the signal circuit of the IAT sensor for a short to ground or a short to the IAT low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 and Connector Repairs in Wiring Systems. 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 and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
8 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the ECM. Refer to Engine Control Module Replacement . 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 | |
