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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Monte Carlo 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1111 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage

Object Number: 402814 Size: SF
OBD II Symbol Description Notice
Engine Controls Components
Cell 21: Engine Data Sensors-A/C Refrig Press, TP, MAP, ECT, IAT
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 Running the DTC
    • No ECT sensor, MAF sensor or VSS DTCs present
    • The engine has been running for over 3 minutes.
    • Engine coolant temperature is greater than 60°C (140°F).
    • Mass air flow is less than 12 g/s.
    • Vehicle speed is less than 35 mph.

Conditions for Setting the DTC

IAT signal voltage intermittently indicates an intake air temperature less than -34°C (-30°F).

Action Taken When the DTC Sets

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

Conditions for Clearing the MIL/DTC
    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction free warm-up cycles.
    • The PCM receives a clear code command from the scan tool.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at the PCM or sensor.
        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 .

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 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

Is DTC P1106, P1115, and/or P1121 also set?

--

Go to Step 6

Go to Step 4

4
  1. Check for a poor sensor ground circuit terminal connection at the IAT sensor. Refer to Intermittents and Poor Connections Diagnosis or Repairing Connector Terminals .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 10

Go to Step 5

5
  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 Intermittents and Poor Connections Diagnosis or Repairing Connector Terminals .

Was a problem found?

--

Go to Step 10

Go to Step 6

6
  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 10

Go to Step 7

7
  1. Check the IAT signal circuit between the IAT sensor connector and the PCM for an intermittent short to voltage. Refer to Wiring Repairs .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 10

Go to Step 8

8
  1. Check for a poor sensor ground circuit terminal connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis or Repairing Connector Terminals .

Was a problem found?

--

Go to Step 10

Go to Step 9

9
  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 10

Go to Diagnostic Aids

10
  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