Diagnostic Instructions
DTC Descriptors
DTC 023: Intake Air Temperature (IAT) Sensor Circuit High Voltage
DTC 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
Engine Controls Schematics
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
With the 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 of the IAT sensor.
Important: The DTCs must be cleared or a temperature of 20°C (68°F) will be displayed on the scan tool.
- Ignition ON, verify that the IAT sensor parameter is at -40°C (-40°F).
| ⇒ | If greater than -40°C (-40°F), test the signal circuit of the IAT sensor for a short to ground. If the circuit/connections test normal, replace the engine control module (ECM). |
- Test for less than 0.5 volt between the low reference circuit of the IAT sensor and the negative terminal of the battery.
| ⇒ | If greater than 0.5 volt, test the low reference circuit of the IAT sensor for a short to voltage. If the circuit/connections test normal, replace the ECM. |
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit of the IAT sensor and the negative terminal of the battery.
| ⇒ | If greater than 5 ohms, test the low reference circuit of the IAT sensor for an open/high resistance. If the circuit/connections test 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.
- Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the IAT sensor and verify the IAT sensor parameter is greater than 180°C (356°F).
| ⇒ | If less than 180°C (356°F), test the signal circuit of the IAT sensor for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM. |
- If all circuits/connections test normal, test or replace the IAT sensor.
Component Testing
- Ignition OFF, disconnect the harness connector of the intake air temperature (IAT) sensor.
Important: A thermometer can be used to test the sensor off the vehicle.
- 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.
| ⇒ | If the resistance Vs. temperature is not within 5 percent, replace the IAT sensor. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
