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P0071






P0071-AMBIENT AIR TEMPERATURE SENSOR PERFORMANCE





For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.

Theory of Operation

Ambient Air Temperature (AAT) sensor performance looks at the outputs of three temperature sensors and compares them under cold start conditions. Following a start to run time delay, the outputs of the AAT, Engine Coolant Temperature (ECT), and Intake Air Temperature (IAT) sensor will be compared. If the ECT and IAT sensors agree and the AAT sensor does not agree, the AAT sensor is declared as irrational. If declared irrational, a second comparison will be done after a short drive cycle.

- When Monitored:
Engine off time is greater than 480 minutes and the vehicle has been driven for one minute over 35 mph. Ambient temperature is greater than -64° C (-83° F).

- Set Condition:
The Powertrain Control Module (PCM) compares the AAT, ECT and IAT sensor values. If ECT and IAT sensors agree with each other but ambient AAT sensor does not agree with them, the AAT sensor is declared as irrational. Two Trip Fault. Three good trips to turn off the Malfunction Indicator Lamp (MIL).





WARNING: On vehicles equipped with the high voltage system, you must thoroughly read and follow all High Voltage Safety procedures. In addition, before performing any diagnostic or service procedure near a high voltage component, you must perform the High Voltage Power Down. Failure to follow these instructions may result in possible serious or fatal injury

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE Diagnostic Trouble Code (DTC)

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

1. Turn the ignition off.
2. If possible, allow the vehicle to sit with the ignition off for more than 480 minutes in an environment where the temperature is consistent and above -7° C (19.4° F).
3. Test drive the vehicle. The vehicle must exceed 48 km/h (30 mph) during the test drive. Do not cycle the ignition off when the test drive is completed.
4. Using the scan tool, select View DTCs.

Is the DTC active or pending at this time?

Yes

- Go To 2

No

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition Test.

2. AMBIENT AIR TEMPERATURE
1. Turn the ignition off.
2. Allow the vehicle to sit with the ignition off in an environment where the temperature is consistent and above -7° C (19.4° F) until the engine coolant temperature is equal to ambient temperature.
3. Turn the ignition on.
4. Using the scan tool, compare the AAT, ECT, and IAT sensor values.

Is the AAT sensor value within 10° C (18° F) of the other two sensor values?

Yes

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition Test
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. AAT SENSOR VOLTAGE
1. Turn the ignition off.
2. Disconnect the AAT sensor electrical connector.
3. Ignition on, engine not running.
4. Using the scan tool, read the AAT sensor voltage.

NOTE: The sensor voltage should be approximately 5.0 Volts (plus or minus 0.1 volt) with the connector disconnected.

Does the scan tool display the voltage as described above?

Yes

- Go To 4

No

- Go To 5

4. AAT SENSOR




1. Turn the ignition off.
2. Connect a jumper wire between the (G31) AAT signal circuit and the (G931) sensor ground circuit in the Ambient Air Temperature Sensor electrical connector.
3. Turn the ignition on.
4. Using the scan tool, read the AAT sensor voltage.

NOTE: The sensor voltage should be approximately 0 Volts (plus or minus 0.1 Volt)with the jumper wire in place.

Does the scan tool display the voltage as described above?

Yes

- Verify there is good pin to terminal contact in the AAT sensor and Front Control Module (FCM) electrical connectors. Replace the AAT sensor if no problems were found with the connectors.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 5 NOTE: Remove the jumper wire before continuing.


5. (G31) AAT SIGNAL CIRCUIT HIGH RESISTANCE
1. Turn the ignition off.
2. Reconnect the AAT sensor electrical connector.
3. Using a voltmeter, perform a voltage drop test. Backprobe the (G31) AAT signal circuit at the AAT sensor harness connector and the FCM C2 electrical connector.
4. Start the engine and allow it to reach normal operating temperature.
5. Monitor the voltmeter.

Is the voltage less than 0.5 Volt?

Yes

- Go To 6

No

- Repair the excessive resistance in the (G31) AAT signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

6. (G931) SENSOR GROUND CIRCUIT HIGH RESISTANCE
1. Turn the ignition off.
2. Using a voltmeter, perform a voltage drop test. Backprobe the (G931) sensor ground circuit at the AAT sensor electrical connector and the FCM C2 electrical 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 may result in possible serious or fatal injury.

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

Is the voltage less than 0.5 Volt?

Yes

- Go To 7

No

- Repair the excessive resistance in the (G931) sensor ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

7. (G31) AAT SIGNAL CIRCUIT SHORTED TO VOLTAGE




1. Turn the ignition off.
2. Disconnect the FCM C2 electrical connector.
3. Ignition on, engine not running.
4. Measure the voltage on the (G31) AAT signal circuit in the AAT sensor electrical connector.

Is there any voltage present?

Yes

- Repair the short to voltage in the (G31) AAT signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 8

8. (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Measure the resistance between ground and the (G31) AAT signal circuit in the AAT sensor electrical connector.

Is the resistance less than 100 ohms?

Yes

- Repair the short to ground in the (G31) AAT signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 9

9. (G31) AAT SIGNAL CIRCUIT SHORTED TO THE (G931) SENSOR GROUND CIRCUIT




1. Measure the resistance between the (G931) sensor ground circuit and the (G31) AAT signal circuit in the AAT Sensor electrical connector.

Is the resistance below 5 ohms?

Yes

- Repair the short between the (G931) sensor ground circuit and the (G31) AAT signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 10

10. FRONT CONTROL MODULE (FCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the AAT sensor and the FCM.
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify there is good pin to terminal contact in the AAT sensor and FMC electrical connectors.
4. Search for any Technical Service Bulletins (TSBs) that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform BODY VERIFICATION TEST VER - 1. Body Verification Test.

No

- Replace the FMC.
- Perform BODY VERIFICATION TEST VER - 1. Body Verification Test.

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