P0071-AMBIENT AIR TEMPERATURE SENSOR PERFORMANCE

For a complete wiring diagram Refer to Section 8W.

Theory of Operation

Ambient 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 intake air temperature sensors agree and the ambient air temperature does not agree, the ambient 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 (18 degrees F) of the other two temperature sensors. Two Trip Fault. Three good trips to turn off the MIL.

Possible Causes

(G31) AAT SIGNAL CIRCUIT HIGH RESISTANCE

(G931) SENSOR GROUND HIGH RESISTANCE

AMBIENT AIR TEMPERATURE SENSOR

TOTALLY INTEGRATED POWER MODULE (TIPM)

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

Diagnostic Test

1. ACTIVE DTC

NOTE: Diagnose any CAN - C Communication DTCs before continuing.

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. AAT SENSOR VOLTAGE ABOVE 4.6 VOLTS

Turn the ignition off.
Disconnect the AAT sensor harness connector.
Ignition on, engine not running.
With a scan tool, read the AAT voltage.

Is the voltage above 4.6 volts?

Yes

Go To 3

Go To 4

3. AAT SENSOR

Connect a jumper wire between the (G31) AAT Signal circuit and the (G931) Sensor ground circuit in the AAT Sensor harness connector.
With a scan tool, read the AAT voltage.

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

Yes

Replace the AAT Sensor.

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

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

4. (G31) AAT SIGNAL CIRCUIT HIGH RESISTANCE

Turn the ignition off.
Reconnect the AAT sensor harness connector.
Using a voltmeter perform a voltage drop test. Backprobe the (G31) AAT Signal circuit at the AAT sensor harness connector and the C4 TIPM harness connector.
Start the engine and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 volts?

Yes

Go To 5

Repair the excessive resistance in the (G31) AAT Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

5. (G931) SENSOR GROUND CIRCUIT HIGH RESISTANCE

Turn the ignition off.
Using a voltmeter perform a voltage drop test. Backprobe the (G931) Sensor ground circuit at the AAT sensor harness connector and the C4 TIPM harness connector.

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 volts?

Yes

Go To 6

Repair the excessive resistance in the (G931) Sensor ground circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

6. TOTALLY INTEGRATED POWER MODULE

NOTE: Before continuing, check the TIPM 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 BODY VERIFICATION TEST VER - 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE)

Replace the Totally Integrated Power Module per Service Information.
Perform BODY VERIFICATION TEST VER - 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE)