P0071-AMBIENT AIR TEMPERATURE SENSOR PERFORMANCE
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° C (38° F).
- Set Condition:
After a calibrated amount of cool down time the BCM compares the ECT Sensor, IAT Sensor, and the Ambient Air Temp Sensor values. If the IAT Sensor value is not within 10° C (50° F) of the other two temperature sensors. Two Trip Fault. Three good trips to turn off the MIL.
| Possible Causes |
| (G31) AAT SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE |
| (G31) AAT SIGNAL CIRCUIT OPEN |
| (K300) SENSOR GROUND CIRCUIT OPEN |
| (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND |
| (G31) AAT SIGNAL CIRCUIT SHORTED TO THE (K300) SENSOR GROUND CIRCUIT |
| AMBIENT AIR TEMPERATURE SENSOR |
| CAN C BUS CIRCUITS OPEN OR SHORTED |
| BCM |
| BCM |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
Diagnostic Test
1. ACTIVE DTCNOTE: 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
No
- Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2. (G31) AAT SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the C2 BCM harness connector.
Disconnect the AAT Sensor harness connector.
NOTE: Visually inspect both the component and the BCM connectors. Look for damaged, partially broken wires, and backed out or corroded terminals.
Ignition on, engine not running.
Measure the voltage on the (G31) AAT Signal circuit in the AAT Sensor harness connector.
Is the voltage above 5.2 volts?
Yes
- Repair the short to voltage in the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go To 3
3. AAT SENSOR VOLTAGE ABOVE 4.6 VOLTS
Turn the ignition off.
Connect the C2 BCM 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 4
No
- Go To 7
4. AAT SENSOR
Connect a jumper wire between the (G31) AAT Signal circuit and the (K300) 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)
No
- Go To 5
NOTE: Remove the jumper wire before continuing.
5. (G31) AAT SIGNAL CIRCUIT OPEN
Turn the ignition off.
Disconnect the C2 BCM harness connector.
Measure the resistance of the (G31) AAT Signal circuit from the AAT Sensor harness connector to the C2 BCM harness connector.
Is the resistance below 5.0 ohms?
Yes
- Go To 6
No
- Repair the open in the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
6. (K300) SENSOR GROUND CIRCUIT OPEN
Measure the resistance of the (K300) Sensor ground circuit from the AAT Sensor harness connector to the C2 BCM harness connector.
Is the resistance below 5.0 ohms?
Yes
- Go To 9
No
- Repair the open in the (K300) Sensor ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
7. (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C2 BCM harness connector.
Measure the resistance between ground and the (G31) AAT Signal circuit in the AAT Sensor harness connector.
Is the resistance below 100 ohms?
Yes
- Repair the short to ground in the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go To 8
8. (G31) AAT SIGNAL CIRCUIT SHORTED TO THE (K300) SENSOR GROUND CIRCUIT
Measure the resistance between the (G31) AAT Signal circuit and the (K300) Sensor ground circuit in the AAT Sensor harness connector.
Is the resistance below 5.0 ohms?
Yes
- Repair the short between the (K300) Sensor ground circuit and the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
- Go To 9
9. BCM
NOTE: Before continuing, check the BCM 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 the BODY VERIFICATION TEST. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE)
No
- Replace the Body Control Module per Service Information.
- Perform the BODY VERIFICATION TEST. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE)