P0072

SYMPTOM
P0072-AMBIENT AIR TEMPERATURE SENSOR CIRCUIT LOW

WHEN MONITORED
The ignition key on.

SET CONDITION
Ambient Temperature Sensor is less than 0.078 of a volt at the PCM for 2.8 seconds. One Trip Fault. Three good trips to turn off the MIL.

POSSIBLE CAUSES
- (G31) MT SIGNAL CIRCUIT SHORTED TO GROUND
- (G31) ATT SIGNAL CIRCUIT SHORTED TO THE (G931) SENSOR GROUND CIRCUIT
- AMBIENT AIR TEMPERATURE SENSOR
- FRONT CONTROL MODULE

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Scan Tool Testing and Procedures

DIAGNOSTIC TEST
1. AAT SENSOR VOLTAGE BELOW 0.078 OF A VOLT





Note: Diagnose any CAN - C Communication DTCs before continuing.

Ignition on, engine not running.
With a scan tool, read the Ambient Air Temperature Sensor voltage.
Is the voltage below 0.078 of a volt?
Yes>> Go To 2
No>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Powertrain Verification Test - Ver 5

2. CHECKING AAT SENSOR





Turn the ignition off.
Disconnect the Ambient Air Temperature Sensor harness connector.
Ignition on, engine not running.
With a scan tool, read the MT Sensor voltage.
Is the voltage above 4.6 volts?
Yes>> Replace the Ambient Temperature Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 3

3. (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND





Turn the ignition off.
Disconnect the C2 FCM harness connectors.
Measure the resistance between ground and the (G31) MT Signal circuit in the MT Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short to ground in the (G31) MT Signal circuit in the MT Sensor harness connector.
No>> Go To 4

4. (G31) AAT SIGNAL CIRCUIT SHORTED TO THE (G931) SENSOR GROUND CIRCUIT





Measure the resistance between the (G931) Sensor ground circuit and the (G31) MT Signal circuit in the MT Sensor harness connector.
Is the resistance below 5.0 ohms?
Yes>> Repair the short between the (G931) Sensor ground circuit and the (G31) MT Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 5

5. FRONT CONTROL MODULE

Note: Before continuing, check the FCM 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 BODY VERIFICATION TEST VER-1.
No>> Replace and program the Front Control Module per Service Information. Perform BODY VERIFICATION TEST VER-1.