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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 DeVille 🢒 DTC 🢒 DTC P1112 Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage

Object Number: 12979 Size: SF
Engine Controls Components
Cell 20: Engine and Fuel Tank Sensors
OBD II Symbol Description Notice
ESD Notice
ESD Notice

Circuit Description

The Intake Air Temperature (IAT) sensor is a thermistor, or variable resistor, that varies resistance based on temperature. As the temperature of the sensor increases, resistance decreases. High temperature will result in a low signal voltage. DTC P1112 sets when the PCM sees an IAT sensor reading of 151°C (304°F) or more when the coolant is less than 110°C (230°F).

Conditions for Running the DTC
    •  DTCs P0112, P0113, P0117 and P0118 not set.
    •  ECT 110°C or less.
    •  Vehicle speed 15 MPH or greater.

Conditions for Setting the DTC

IAT 151°C (304°F) or more.

Action Taken When the DTC Sets
    •  The Malfunction Indicator Lamp (MIL) will not illuminate.
    •  No message will be displayed.

Conditions for Clearing the DTC
    •  A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.
    •  A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
    • Use a scan tool to clear DTCs.
    • Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description .

Diagnostic Aids

If a faulty sensor is suspected refer to Temperature vs Resistance table.

DTC P1112 may set due to random engine backfires which could cause a sudden increase in intake temperature. Check if customer complained of this type of situation and make repairs if necessary.

Test Description

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

  1. If DTC P0111 is also set, diagnose it first because it may help to pinpoint a faulty IAT sensor.

    2.

  2. Checking for intermittent circuit faults that may cause a low IAT reading.

Step

Action

Value(s)

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

Turn the key ON.

Is DTC P0111 or P0112 also set?

--

Go to DTCs that are set

Go to Step 3

3

  1. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
  2. Disconnect PCM connectors C1 and C2.
  3. Examine terminal 71 of C1 and terminal 76 of C2.
  4. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis

Go to Step 4

4
  1. Disconnect IAT sensor connector.
  2. Examine terminals A and B.
  3. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis

Go to Step 5

5
  1. Check IAT sensor signal circuit for possible shorts to ground.
  2. Repair circuit(s) if needed.

Was a repair made to any circuit?

--

Go to Powertrain Control Module Diagnosis

Fault not present. Refer to Diagnostic Aids