Diagnostic Instructions
| • | Perform the Powertrain On Board Diagnostic (OBD) System Check prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
DTC Descriptors
DTC 23: Intake Air Temperature (IAT) Sensor Circuit Low TemperatureDTC 25: Intake Air Temperature (IAT) Sensor Circuit High Temperature
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
IAT Sensor Signal | 25 | 23 | 23 | -- |
Low Reference | -- | 23 | 23 | -- |
Typical Scan Tool Data
Circuit | Short to Ground | Open | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Varies with ambient temperature | |||
IAT Sensor Signal | 141°C (286°F) | -40°C (-40°F) | -40°C (-40°F)* |
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)* |
* Internal ECM or sensor damage may occur if the circuit is shorted to B+. | |||
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 |
Diagnostic Aids
If the vehicle has set overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F).
Reference Information
Schematic Reference
Connector End View Reference
Engine Control Module Connector End Views
Electrical Information Reference
Scan Tool Reference
Engine Control Module Scan Tool Information
Circuit/System Verification
Engine idling for 4 minutes, observe the DTC information with a scan tool. DTCs 23 or 25 should not set.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the IAT sensor.
- Test for less than 5 ohms between the low reference circuit terminal B and ground.
- Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal A and ground.
- 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. |
| ⇒ | If less than the specified range, test the signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector at the 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.
| • | Engine Control Module Replacement for ECM replacement, setup, and programming. |
