P1112

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor contains a semiconductor device which changes resistance based on temperature. The IAT sensor is located in the air intake passage of the engine air induction system. The IAT sensor has a signal circuit and a ground circuit. The Powertrain Control Module (PCM) applies about 5 volts on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine intake air temperature.

When the intake air is cold, the sensor resistance is high, and the PCM signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM will sense a high signal voltage or a low temperature. When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. Therefore the PCM will sense a low signal voltage or a high temperature. If the PCM detects an excessively low IAT signal voltage intermittently, (a high temperature indication), this DTC will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0117, P0118, P0125, P0502, P0503, P1114, or P1115 are not set.
^ The engine has been running for over 10 seconds.
^ The vehicle speed is more than 40 km/h (25 mph).

CONDITIONS FOR SETTING THE DTC
IAT signal voltage intermittently indicates an intake air temperature more than 134°C (274°F).

ACTION TAKEN WHEN THE DTC SETS
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A History DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ The current DTC will clear when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL diagnostic trouble code.
^ Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description, Clearing Diagnostic Trouble Codes.

DIAGNOSTIC AIDS

NOTE: Refer to Connector Test Adapter kit J 35616-A Notice in Service Precautions

Check for the following conditions:
^ A faulty connection at the PCM - Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
^ A damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the malfunction.
^ A skewed or incorrectly calibrated IAT sensor - Refer to the Temperature vs Resistance. [1][2]Computers and Control Systems

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

If the condition is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-5:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that the malfunction is present.
3. If DTC P1112 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance. The table may be used to test the IAT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the IAT sensor. [1][2]Computers and Control Systems