P0072 - Ambient Air Temperature Sensor Circuit Low

Theory of Operation

The Ambient Air Temperature (AAT) Sensor is located in the driver's door mirror. The Driver's Door Module (DDM) receives the data from the AAT sensor and sends it to the Body Control Module (BCM). The BCM then passes the data on to the Powertrain Control Module (PCM). There are two rationality tests. The first test is: Ignition on/engine running. The second test is: After an eight hour cold soak, at key on the readings for the AAT, Charge Air Cooler (CAC) temperature (D2, DJ), Intake Manifold Temperature (DD, DP), and the Engine Coolant Temperature (ECT) Sensors are all compared. If the temperatures differ by more than a calibrated amount, then the appropriate sensor fault code would be recorded. The PCM rationality check looks at the temperature reading from the sensor over time and ensures that it changes with the engine running. If the sensor reading does not change over a calibrated time limit, the fault will be recorded.

When Monitored and Set Conditions

When Monitored: This diagnostic runs continuously when the following conditions are met:
• With the ignition on.

Set Conditions:
• The Powertrain Control Module (PCM) detects that the Ambient Air Temperature (AAT) Signal circuit
has fallen below a calibrated threshold.

Default Actions:
• The MIL is illuminated.

Possible Causes

AAT SENSOR SIGNAL CIRCUIT SHORTED TO GROUND

AAT SENSOR SIGNAL CIRCUIT SHORTED TO DRIVER MIRROR HEATER RETURN CIRCUIT

AMBIENT AIR TEMPERATURE (AAT) SENSOR

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTCBased Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

Diagnostic Test

1. ACTIVE DTC

NOTE: There is no direct circuit input from the Ambient Air Temperature Sensor to the PCM.

NOTE: If there are any Loss of Communication DTCs related to the DDM present in the Body Control Module or elsewhere, perform those diagnostics before continuing with this diagnostic tree.

NOTE: If there are any other DTCs related to the Ambient Air Temperature Sensor present in the BCM, DDM, or any other module, perform those diagnostics before continuing with this diagnostic tree.

1. Turn the ignition on.
2. With the scan tool, record all Freeze frame data.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 75 seconds.
5. Turn the ignition on.
6. With the scan tool, read DTCs.
Did DTC P072 reset?

Yes
• Go To 2

No
• Perform the INTERMITTENT CONDITION diagnostic procedure. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

2. CHECK THE (G31) AAT SIGNAL CIRCUIT FOR A SHORT TO GROUND

1. Turn the ignition off.
2. Disconnect the AAT Sensor harness connector.
NOTE: Check connectors - Clean/repair as necessary.
3. Measure the resistance between ground and the (G31) AAT Signal circuit.
Is the resistance below 10k Ohms?

Yes
• Repair the (G31) AAT Signal circuit for a short to ground.
• Perform the POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based
Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

No
• Go To 3

3. CHECK FOR THE (G31) AAT SIGNAL CIRCUIT SHORTED TO THE (C160) DRIVER MIRROR HEATER RETURN CIRCUIT

1. Disconnect the Driver Door Module.

2. Measure the resistance between the (G31) AAT Signal circuit and the (C160) Driver Mirror Heater Return circuit at the AAT Sensor harness connector. Is the resistance below 10k Ohms?

Yes

• Repair the short between the ((G31) AAT Signal circuit and the (C160) Driver Mirror Heater Return circuit.

• Perform POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

No

• Replace the Ambient Air Temperature Sensor in accordance with the Service Information.(Refer to 24 - Heating and Air Conditioning/Controls/SENSOR, Ambient Temperature/Removal)

• Perform the POWERTRAIN VERIFICATION TEST - 6.7L. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).