P0072 INLET AIR TEMP SENSOR VOLTAGE TOO LOW (DIESEL)

When Monitored and Set Condition:

When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The circuit voltage to the ECM falls below a calibrated threshold for a certain period of time.

POSSIBLE CAUSES

• SENSOR OUT OF SPEC
• INTERMITTENT CONDITION
• HARNESS SHORTED
• (Y501) 5-VOLT SUPPLY OPEN
• HARNESS SHORTED (ECM SIDE)
• INTERMITTENT CONDITION
• ECM

DIAGNOSTIC PROCEDURE

NOTE: Refer to VERIFICATION TESTS for appropriate verification test procedures.

1. Turn the ignition off. Disconnect the Inlet Air Temp sensor harness connector. Check connectors - Clean/repair as necessary. Measure the resistance of the temperature sensor. Is the resistance between 300 and 90k ohms?
   Yes --> Go To 2
   No --> Replace the sensor. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
2. Reconnect the Inlet Air Temp Sensor harness connector. Turn the ignition on. With the DRBIII®, erase DTCs. With the DRBIII®, read DTCs. Did the DTC return?
   Yes --> Go To 3
   No --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
3. Turn the ignition off. Disconnect the inlet Air Temp sensor harness connector. Disconnect the ECM harness connector. Check connectors - Clean/repair as necessary. Measure the resistance between the engine ground and the (K69) temperature sensor signal circuit at the sensor connector. Is the resistance more than 100 k ohms?
   Yes --> Go To 4
   No --> Replace or Repair the shorted harness. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
4. Measure the resistance between the (K69) signal circuit and all other circuits at the ECM harness connector. Is the resistance more than 100 k ohms?
   Yes --> Go To 5
   No --> Repair or replace the ECM harness shorted. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
5. Reconnect the ECM harness connector. Turn the ignition on. Measure the voltage between the (Y501) supply circuit and the (Y502) return circuit in the Air Temp sensor harness connector. Is the voltage between 4.5 and 5.5 volts?
   Yes --> Go To 6
   No --> Go To 7
6. Reconnect the Air Temp sensor harness connector. Reconnect the ECM harness connector. With the DRBIII®, erase DTCs. While monitoring with DRBIII®, disconnect the Air Temp sensor harness connector. Did the DTC P0073 set?
   Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure).  Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
7. Disconnect the ECM harness connectors. Measure the voltage at the (Y501) 5-volt supply circuit at he ECM harness connector. Is the voltage between 4.5 and 5.5 volts?
   Yes --> Fix or repair the (Y501) 5-volt supply circuit open. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).