P0071 - PERFORMANCE OF THE AMBIENT AIR TEMPERATURE SENSOR

The AAT (Ambient Air Temperature Sensor) changes the outside air temperature into an electrical signal that it sends to the PCM (Powertrain Control Module). At the same time, the PCM uses this signal to display the outside air temperature and modify the air conditioning operation.

The PCM also receives signals from the ECT (Engine Coolant Temperature) Sensor and IAT (Intake Air Temperature) Sensor, which are compared to the AAT Sensor once the ignition switch is turned on after a cool-down period. If there is a narrow range of variation in all of these inputs, the DTC P0071 OBDII code will be set and the Check Engine light will turn on.

• MIL light ON.
• The air conditioning is not working properly.
• The outside temperature may not be read accurately by the appropriate instruments.

These are the most common causes to set the P0071 OBD2 diagnostic code:

• The AAT Sensor may have an open in its signal circuit.
• There may be a short to ground or voltage in the AAT Sensor signal circuit.
• The AAT Sensor may be faulty.

Steps to troubleshoot the P0071 OBDII error code:

• Check for the Technical Service Bulletins (TSB).
• Check the wires leading to the AAT Sensor. Look for burn spots or rubbing against other components. Also, check the terminals for corrosion. Repair or replace if necessary.
• Use a digital meter and set it to the ohms scale, disconnect the sensor and connect the meter leads to each sensor terminal. Determine the temperature of the sensor, which is the outside temperature at the resistance shown in the specification table. If the resistance shown on the meter is not the same or shows a reading in ohms of 0 or infinite resistance, the sensor must be replaced because it is broken.