Powertrain Control Module (PCM)

P0072-AMBIENT AIR TEMPERATURE SENSOR CIRCUIT LOW

For a complete wiring diagram, refer to the Wiring Information.

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). Following a start to run delay time, the outputs of the ambient, engine coolant and intake air temperature sensors are compared. 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.

- When Monitored:
The ignition key on.

- Set Condition:
Ambient Temperature Sensor is less than the minimum acceptable value. One Trip Fault. Three good trips to turn off the MIL.





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

Diagnostic Test

1. DTC IS ACTIVE
1. Start the engine and allow it to reach normal operating temperature.

WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

NOTE: Diagnose and repair any system voltage DTCs before continuing with this test.

2. With the scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. PCM Intermittent Condition Test.

2. CHECKING AAT SENSOR
1. Turn the ignition off.
2. Disconnect the Ambient Air Temperature Sensor harness connector.
3. Ignition on, engine not running.
4. With the scan tool, read the AAT Sensor voltage.

NOTE: The sensor voltage should be approximately 5.0 Volts (plus or minus.1 of a Volt) with the connector disconnected.

Does the scan tool display the voltage as described above?

Yes

- Verify that there is good pin to terminal contact in the Sensor and Control Module connectors. Replace the Ambient Air Temperature Sensor if no problems were found with the connectors.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 3

3. (G31) AAT SIGNAL CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the C5 Totally Integrated Power Module (TIPM) harness connector.
3. 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. Powertrain Verification Test.

No

- Go To 4

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




1. Measure the resistance between the (G931) AAT return circuit and the (G31) AAT Signal circuit in the AAT Sensor harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Repair the short between the (G931) AAT return circuit and the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 5

5. EXCESSIVE RESISTANCE IN THE (G31) AAT SIGNAL CIRCUIT




1. Measure the resistance of the (G31) AAT Signal circuit between the Ambient Air Temperature Sensor harness connector and the TIPM C5 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 6

No

- Repair the excessive resistance in the (G31) AAT Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. TOTALLY INTEGRATED POWER MODULE (TIPM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the AAT Sensor and the Totally Integrated Power Module (TIPM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Sensor and Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Replace and program the Totally Integrated Power Module (TIPM).
- Perform the BODY VERIFICATION TEST. Body Verification Test.