DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage. Buick GL7 (Export) 2000

For 1990-2009 cars

### Circuit Description

The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5.0 volts through a pull-up resistor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT sensor signal circuit. As the underhood air warms, the sensor resistance becomes lower causing the PCM to monitor a lower voltage. If the PCM detects an excessively low IAT sensor signal voltage, DTC P0112 will set.

### Conditions for Running the DTC

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

• | The engine is running for more than 10 seconds

• | The vehicle speed is more than 40 km/h (25 mph).

### Conditions for Setting the DTC

• | The IAT signal voltage indicates an intake air temperature of more than 135°C (275°F).

• | The above conditions are present for at least 20 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

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

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

Inspect for the following conditions:

• | Poor connection at the PCM. Inspect harness connectors for the following conditions:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal-to-wire connections

• | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | 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 the connectors and the wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.

If DTC P0112 cannot be duplicated, the information included in the Failure Records data can be useful in determining the vehicle mileage since the DTC was last set.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Verifies that the fault is present.

2. If DTC P0112 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance table. The table may be used to test the IAT sensor at various temperatures in order 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. If the IAT sensor appears to be OK, the fault is intermittent. Refer to Diagnostic Aids.

3. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.

#### DTC P0112 IAT Sensor Circuit Low Voltage

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Turn ON the ignition, leaving the engine OFF.
2. With a scan tool, observe the IAT parameter.

Is the IAT parameter more than the specified value?

135°C (275°F)

Go to Step 4

Go to Step 3

3

1. With a scan tool, review and record the Failure Records data.
2. Operate the vehicle within the Failure Records conditions as noted.

Does scan tool indicate DTC P0112 failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

1. Turn OFF the ignition.
2. Disconnect the IAT sensor.
3. Turn ON the ignition, leaving the engine OFF.
4. With a scan tool, observe the IAT parameter.

Is the IAT parameter less than the specified value?

-37°C (-34°F)

Go to Step 6

Go to Step 5

5

1. Turn OFF the ignition.
2. Test the signal circuit of the IAT sensor for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | --
7 | Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 8 | --

8

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Failure Records conditions as noted.

Does the DTC reset?

--

Go to Step 2

System OK