For 1990-2009 cars
Engine Controls Components
TP, MAP, ECT, IAT Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The PCM applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. DTC P1112 will set when the PCM detects an intermittently low signal voltage on the intake air temperature sensor signal circuit.

### Conditions for Running the DTC

• | No active ECT sensor, MAF sensor, or VSS DTCs are present.

• | The engine has been running for over 10 seconds.

• | Vehicle speed is greater than 25 mph.

### Conditions for Setting the DTC

• | The IAT sensor intermittently indicates an intake air temperature greater than 135°C (275°F).

• | The condition is present for longer than 5 seconds.

### Action Taken When the DTC Sets

• | The PCM will not illuminate the malfunction indicator lamp (MIL).

• | The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

### Conditions for Clearing the MIL/DTC

• | A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool Clear Info function.

### Diagnostic Aids

Check for the following conditions:

• | Poor 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.

• | 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.

• | Skewed or mis-scaled IAT Sensor.

| Refer to Temperature Versus Resistance table.

If DTC P1112 cannot be duplicated, the information included in the Freeze Frame/Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Verifies that the fault is present.

2. If DTC P1112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature Vs. Resistance Values Table. 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.

#### DTC P1112 - IAT Sensor Circuit Intermittent Low Voltage

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | With a scan tool, select Diagnostic Trouble Codes (DTC). Does the scan tool indicate DTC P0112 set? | -- | Go to DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage | Go to Step 3
3 | Test the IAT signal for an intermittent short to ground. Refer to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 4 | Go to Diagnostic Aids
4 |

1. Use the scan tool in order to record Fail Records and clear DTCs
2. Operate the vehicle within Fail Records conditions.

Does the DTC reset?

--

Go to Step 2

System OK