P0072
P0072-AMBIENT AIR TEMPERATURE SENSOR CIRCUIT LOWP0072-Ambient Air Temperature Sensor Circuit Low:
Theory of Operation
Ambient Air Temperature Sensor performance looks at the outputs of three temperature sensors and compare 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
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) AAT signal circuit shorted to ground
- (G31) AAT 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.
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.
Q: Is the voltage below 0.078 of a volt?
YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
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 AAT Sensor voltage.
Q: Is the voltage above 4.6 volts?
YES: Replace the Ambient Temperature Sensor. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 3
3. (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C2 FCM harness connector.
Measure the resistance between ground and the (G31) AAT Signal circuit in the AAT Sensor harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short to ground in the (G31) AAT Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
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) AAT Signal circuit in the AAT Sensor harness connector.
Q: Is the resistance below 5.0 ohms?
YES: Repair the short between the (G931) Sensor ground circuit and the (G31) AAT Signal circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
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.
Q: Were there any problems found?
YES: Repair as necessary. Perform BODY VERIFICATION TEST VER - 1. Body Verification Test
NO: Replace and program the Front Control Module. Perform BODY VERIFICATION TEST VER - 1. Body Verification Test