P0071 - Ambient Air Temperature Sensor Performance: Notes

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 Totally Integrated Power Module (TIPM) to the Powertrain Control Module (PCM). The AAT sensor is a variable resistor that measures the ambient air temperature. The TIPM 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.

Possible Causes
(G31) AAT SIGNAL CIRCUIT HIGH RESISTANCE
(G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND
(G31) AAT SIGNAL CIRCUIT SHORTED TO THE (G931) SENSOR GROUND CIRCUIT
(G31) AAT SIGNAL CIRCUIT SHORTED TO VOLTAGE
(G931) SENSOR GROUND HIGH RESISTANCE
AMBIENT AIR TEMPERATURE SENSOR
CAN C BUS CIRCUITS
TOTALLY INTEGRATED POWER MODULE (TIPM)
POWERTRAIN CONTROL MODULE (PCM)

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