Schematic Reference: Engine Controls Schematics
Circuit Description
The intake air temperature (IAT) sensor is a thermistor (a variable resistor whose conductive value changes with temperature) in series with a fixed resistor in the engine control module (ECM). The ECM applies 5 volts to the IAT sensor. The ECM monitors the voltage across the IAT sensor and converts it into a temperature reading. When the outside air temperature is cold the IAT sensor resistance is high, and when the outside air temperature is warm the IAT sensor resistance is low. Therefore, when the air temperature is cold the ECM will receive a high voltage input, and when the air temperature is warm the ECM will receive a low voltage input.
Conditions for Setting the DTC
| • | The ignition is ON. |
| • | IAT signal voltage indicates an intake air temperature greater than 139°C (282°F). |
| • | The above condition is met for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
| • | The ECM will enter the fail-safe function and assume the intake air temperature is 23°C (73°F). |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn off after three consecutively passing cycles without a fault present. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTC(s) can be cleared by using a scan tool or by disconnecting the ECM battery feed. |
Diagnostic Aids
Check for any of the following conditions:
| • | A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault. |
| • | When replacing the IAT sensor the Temperature to Resistance Value scale may be used to test the sensor at various temperature levels to evaluate the possibility of a shifted (incorrectly calibrated) sensor. Refer to Temperature Versus Resistance . A shifted sensor could result in poor driveability complaints. |
An intermittent malfunction may be caused by a fault in the IAT sensor circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
If the 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 in the Diagnostic Table.
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The Powertrain OBD System Check 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.
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This step will determine if fault is present.
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Review Freeze Frame data to determine when the DTC set. Always record this information.
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This step determines if the fault is caused by a shorted signal return circuit or by a malfunctioning IAT sensor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Is the IAT display at or greater than the specified value? | 139°C (282°F) | |||
Is a DTC P0112 set? | -- | Go to Diagnostic Aids | ||
Is the IAT display at or below the specified value? | -40°C (-40°F) | |||
5 |
Is the IAT sensor signal circuit shorted to ground? | -- | ||
6 | Check the IAT sensor ground circuit for a short to voltage. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a repair necessary? | -- | ||
7 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement. Is the action complete? | -- | -- | |
8 | Repair the IAT sensor signal (input) circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
9 | Replace the ECM. Refer to Engine Control Module Replacement. Is the action complete? | -- | -- | |
10 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
