Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC 023: Intake Air Temperature (IAT) Sensor Circuit High VoltageDTC 025: Intake Air Temperature (IAT) Sensor Circuit Low Voltage
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.
The following table illustrates the difference between temperature, resistance, and voltage:
IAT | IAT Resistance | IAT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
Conditions for Setting the DTC
023
| • | The engine run time is more than 120 seconds. |
| • | The IAT sensor signal voltage indicates a temperature above 146°C (295°F). |
| • | This DTC runs continuously when the above conditions are met. |
025
| • | The engine run time is more than 120 seconds. |
| • | The IAT sensor signal voltage indicates a temperature less than -35°C (-31°F). |
| • | This DTC runs continuously when the above conditions are met. |
Diagnostic Aids
| • | If the vehicle has set overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F). |
| • | High resistance on either the IAT sensor signal circuit or the IAT sensor low reference circuit may not set a DTC. |
Reference Information
Schematic Reference
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Engine idling for 4 minutes, observe the DTC information with a scan tool. DTCs 023 or 025 should not set.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the IAT sensor.
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal B and ground.
- Ignition ON, verify the scan tool IAT sensor parameter is at -40°C (-40°F).
- Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool IAT sensor parameter is greater than 180°C (356°F).
- If all circuits test normal, test or replace the IAT sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.
| ⇒ | If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.
| ⇒ | If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector at the intake air temperature (IAT) sensor.
- Test the IAT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.
Important: A thermometer can be used to test the sensor off the vehicle.
| ⇒ | If not within the specified range, replace the IAT sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for engine control module replacement, setup, and programming |
