Circuit Description
The intake air temperature (IAT) sensor uses a thermistor to control the signal voltage to the engine control module (ECM). The ECM supplies a 5-volt reference and a ground to the sensor. When the air is cold, the resistance is high, therefore the IAT signal voltage will be high. If the intake air is warm, the resistance is low, therefore the IAT signal voltage will be low.
Conditions for Running the DTC
| • | IAT is less than -42°C (-44°F). |
| • | Vehicles speed is less than 25 km/h (16 mph). |
| • | Engine run time is greater than 120 seconds. |
| • | Engine coolant temperature (ECT) is above 70°C (158°F). |
| • | Calculated air flow is less than 15 g/second. |
| • | DTC P0502 is not set. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trip with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and 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
| • | If the vehicle is at ambient temperature, compare the IAT sensor to the ECT sensor. The IAT sensor and the ECT sensor should be relatively close to each other. |
| • | Use the Temperature vs. Resistance Values table to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
-
This step simulates a DTC P0112. If the ECM senses the change, the ECM and wiring are OK.
-
This step will determine if the reason the ECM did not sense the change was due to a open ground or signal circuit or malfunctioning ECM.
-
The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | -- | Go to Step 2 | ||
2 |
Is the intake air temperature (IAT) value less than the specified value? | -30°C (-22°C) | Go to Step 4 | Go to Step 3 |
3 |
Is the IAT sensor value less than the specified value? | -30°C (-22°C) | Go to Step 4 | Go to Diagnostic Aids |
Is the IAT sensor value greater than the specified value? | 130°C (266°F) | Go to Step 6 | Go to Step 5 | |
Jumper the IAT sensor signal circuit at terminal 1 to ground. Is the IAT sensor value greater than the specified value? | 130°C (266°F) | Go to Step 7 | Go to Step 8 | |
6 | Inspect for a poor connection at the IAT sensor connector and repair or replace any malfunctioning terminal as needed. Is a repair necessary? | -- | Go to Step 12 | Go to Step 10 |
7 | Inspect the IAT sensor ground circuit for an open and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
8 | Inspect the IAT sensor signal circuit for an open and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 |
9 | Inspect for a poor IAT sensor ground circuit at terminal A32 or a poor IAT sensor signal circuit terminal A23 connection at engine control module (ECM) and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement Did you complete the replacement? | -- | Go to Step 12 | -- |
Did you complete the replacement? | -- | Go to Step 12 | -- | |
12 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 13 | Go to Step 2 |
13 | Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
