P0112 INTAKE AIR TEMPERATURE (IAT) SENSOR VOLTAGE TOO LOW

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

• INTAKE AIR TEMP SENSOR OUT OF SPEC
• INTERMITTENT CONDITION
• (K21) SENSOR SIGNAL CIRCUIT SHORTED TO GROUND CIRCUIT
• WIRING HARNESS SHORTED
• (K72E) 5-VOLT SUPPLY CIRCUIT OPEN
• ECM

DIAGNOSTIC PROCEDURE

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

1. Disconnect the Intake Air Temperature sensor harness connector. Check connectors - Clean/repair as necessary. Measure the resistance of the Intake Air Temp sensor. Is the resistance between 300 and 90k ohms?
   Yes --> Go To 2
   No --> Replace the Intake Air temperature sensor/MAP sensor. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
2. Reconnect the circuit. Turn the ignition on. With the DRBIII®, erase DTCs. With the DRBIII®, read DTCs. Did the DTC reappear?
   Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Go To 3
3. Turn the ignition off. Disconnect the ECM harness connector. Check connectors - Clean/repair as necessary. Measure the resistance between the engine ground and the temperature sensor (K21) signal circuit at the sensor harness connector. Is the resistance more than 100 k ohms?
   Yes --> Go To 4
   No --> Repair or replace the engine wiring harness. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
4. Measure the resistance between the (K21) 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 shorted wiring harness. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
5. Reconnect the ECM harness connector connected. Turn the ignition on. Measure the voltage between the (K72E) 5-volt supply circuit and the (K55) return circuit the sensor harness connector. Is the voltage between 4.5 and 5.5 volts?
   Yes --> Go To 7
   No --> Go To 6
6. Turn the ignition off. Disconnect the ECM harness connector. Measure the voltage at the (K72E) 5-volt supply circuit of the sensor harness connector. Is the voltage between 4.5 and 5.5 volts?
   Yes --> Repair the open (K72E) 5-volt supply circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Go To 7
7. Reconnect the ECM harness connector. Reconnect the intake air temp sensor harness connector. Turn the ignition on. While monitoring with DRBIII®, disconnect the temperature sensor Did the DTC P0113 set?
   Yes --> Clear DTC's, repair complete. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
   No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).