P0111-INTAKE AIR TEMPERATURE SENSOR RATIONALITY

For a complete wiring diagram Refer to Section 8W.

Theory of Operation

Intake Air Temperature Sensor performance looks at the outputs of three temperature sensors and compares them under cold start conditions. Following a start to run delay time, the outputs of the ambient, engine coolant, and intake air temperature sensors will be compared. If the engine coolant and ambient air temperature sensors agree and the intake air temperature does not agree, the intake air temperature sensor is declared as irrational.

When Monitored:
Engine off time is greater than 480 minutes. Ambient temperature is greater than 4 degrees C (38 degrees F).
Set Condition:
After a calibrated amount of cool down time the PCM compares the ECT Sensor, IAT Sensor, and the Ambient Air Temp Sensor values. If the IAT Sensor value is not within 10 degrees C (50 degrees F) of the other two temperature sensors. Two Trip Fault. Three good trips to turn off the MIL.

Possible Causes

EXCESSIVE RESISTANCE IN THE (K21) IAT SIGNAL CIRCUIT

EXCESSIVE RESISTANCE IN THE (K900) SENSOR GROUND CIRCUIT

INTAKE AIR TEMPERATURE SENSOR

PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

Diagnostic Test

1. ACTIVE DTC

Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, select View DTCs.

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.

Is the DTC Active or Pending at this time?

Yes

Go To 2

Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

2. IAT SENSOR VOLTAGE ABOVE 4.6 VOLTS

Turn the ignition off.
Connect the C2 PCM harness connector.
Ignition on, engine not running.
With a scan tool, read the IAT voltage.

Is the voltage above 4.6 volts?

Yes

Go To 3

Go To 4

3. IAT SENSOR

Connect a jumper wire between the (K21) IAT Signal circuit and the (K900) Sensor ground circuit in the IAT Sensor harness connector.
With a scan tool, read the IAT voltage.

Is the voltage below 1.0 volt with the jumper wire installed?

Yes

Replace the IAT Sensor.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 4
NOTE: Remove the jumper wire before continuing.

4. EXCESSIVE RESISTANCE IN THE (K21) IAT SIGNAL CIRCUIT

Turn the ignition off.
Disconnect the C2 PCM harness connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 and #8815-1 to perform diagnosis.

Using a voltmeter perform a voltage drop test. Backprobe the (K21) IAT Signal circuit at the IAT Sensor harness connector and probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Start the engine and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes

Go To 5

Repair the open in the (K21) IAT Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

5. EXCESSIVE RESISTANCE IN THE (K900) SENSOR GROUND CIRCUIT

Turn the ignition off.
Move the voltmeter leads to backprobe the (K900) Sensor Ground circuit at the IAT Sensor harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

Start the engine and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes

Go To 6

Repair the open in the (K900) Sensor ground circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

6. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes

Repair as necessary.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)