P0071

P0071-AMBIENT AIR TEMPERATURE SENSOR PERFORMANCE

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

Theory of Operation

Ambient Air Temperature (AAT) sensor performance looks at the outputs of three temperature sensors and compares them under cold start conditions. The AAT reading is a bussed message from the Body Control Module (BCM) to the Powertrain Control Module (PCM). The AAT sensor is a variable resistor that measures the ambient air temperature. The BCM supplies a 5 volt reference and a ground to the sensors low reference signal circuit. When the AAT is low, the sensor resistance is high. When the AAT is high, the sensor resistance is low. Following a start to run delay time, the outputs of the ambient, engine coolant and intake air temperature sensors are 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. 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 PCM compares the ambient, engine coolant and intake air temperature sensor values. If engine coolant and intake air temperature sensors agree with each other but ambient air temperature does not agree, the ambient air temperature sensor is declared as irrational. Two Trip Fault. Three good trips to turn off the MIL.





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

NOTE: Diagnose any CAN - Communication DTCs in the PCM and any Ambient Air Temperature Sensor DTCs in the BCM 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. With the scan tool, select View DTCs.

Is the DTC Active or Pending at this time?

Yes

- Perform any active Ambient Air Temperature Sensor diagnostic procedures Testing and Inspection.

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.