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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1998 🢒 Firebird 🢒 DTC 🢒 DTC P1111 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage

Object Number: 221729 Size: SF
Engine Controls Components
TP, MAP, ECT, IAT Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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 P1111 will set when the PCM detects an intermittently high signal voltage on the intake air temperature sensor signal circuit.

Conditions for Setting the DTC
    • No ECT sensor, MAF sensor, or VSS DTCs are present
    • The engine has been running for over 3 minutes.
    • Engine coolant temperature is greater than 60°C (140°F).
    • Vehicle speed is less than 56 km/h (35 mph).
    • Mass air flow is less than 12 g/s.
    • IAT signal voltage intermittently indicates an intake air temperature less than -34°C (-29°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 Fail 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.
    • DTC can be cleared by using the scan tool Clear Information function or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at PCM - Inspect harness connectors for the following items:
       - Backed out terminals
       - Improper mating
       - Broken locks
       - Improperly formed or damaged terminals
       - Poor terminal to wire connections
    • 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 fault.
    • Skewed or mis-scaled IAT Sensor.
        Refer to Temperature vs Resistance table.

Reviewing the Fail 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.

DTC P1111 - IAT Sensor Circuit Intermittent High Voltage

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

2

Select DTC info, Last Tst Fail and note any other DTCs set.

Is DTC P0113 also set?

--

Go to DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage

Go to Step 3

3
  1. Check for a poor sensor ground circuit terminal connection at the IAT sensor. Refer to Wiring Repairs .
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 9

Go to Step 4

4
  1. Check for a poor IAT signal circuit terminal connection at the IAT sensor.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 9

Go to Step 5

5
  1. Check the IAT signal circuit between the IAT sensor connector and the PCM for an intermittent open.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 9

Go to Step 6

6
  1. Check the IAT signal circuit between the IAT sensor connector and the PCM for an intermittent short to voltage.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found and repaired?

--

Go to Step 9

Go to Step 7

7
  1. Check for a poor sensor ground circuit terminal connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 9

Go to Step 8

8
  1. Check for an intermittent open in the sensor ground circuit.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 9

Go to Diagnostic Aids

9
  1. Review and record scan tool Fail Records data.
  2. Clear DTCs.
  3. Operate the vehicle within Fail Records conditions as noted.
  4. Using a scan tool, monitor Specific DTC info for DTC P1111.

Does scan tool indicate DTC P1111 failed?

--

Go to Step 2

System OK