Code P1112 Buick: Causes, Symptoms, and Solutions
The code P1112 is an OBD-II code specific to Buick vehicles, related to the Intake Air Temperature (IAT) sensor circuit. This sensor measures the temperature of the air entering the engine, a crucial data point for optimizing the air-fuel mixture.
Meaning of Code P1112
- The IAT sensor is a thermistor: its resistance varies with the air temperature.
- The PCM sends a 5 V reference voltage to the sensor.
- Cold air → High resistance → High signal voltage (e.g., 4.5 V).
- Hot air → Low resistance → Low signal voltage (e.g., 0.5 V).
- The code P1112 is triggered when the PCM detects an abnormal value (voltage out of range) in the IAT sensor circuit.
Possible Causes
- Faulty IAT sensor (damaged thermistor).
- Wiring problems:
- Open or short circuit (signal or ground wires).
- Oxidized, loose, or corroded connector.
- PCM failure (rare).
Common Symptoms
- Check Engine Light illuminated (MIL).
- Unstable idle or difficulty starting.
- Engine overheating or excessive fuel consumption.
- Reduced performance (gear shifting issues, loss of power).
Diagnostic and Repair Procedures
Step 1: Visual Inspection
- Locate the IAT sensor (usually in the intake duct or air filter housing).
- Check the connector and wiring harness for:
- Bent, broken, or corroded pins.
- Damaged or exposed wires.
Step 2: IAT Sensor Test
- Disconnect the sensor and measure its resistance with a multimeter:
- Ambient air (~20°C): Resistance ≈ 2,000–3,000 Ω.
- Hot air (using a hairdryer): Resistance should decrease.
- If the resistance is out of range → Replace the sensor.
Step 3: Electrical Circuit Check
- Turn the ignition on (without starting the engine).
- Measure the reference voltage at the sensor connector:
- Expected: ≈5 V.
- If absent: Check the circuit between the PCM and the sensor.
- Check the sensor ground with a multimeter (continuity between the sensor ground and chassis ground).
Step 4: PCM Test
- If the wiring and sensor are functional, suspect a faulty PCM.
- Confirm with a scan tool by comparing IAT data with an external thermometer.
Solutions
- Replace the IAT sensor if faulty (average cost: €30–€80).
- Repair the wiring or replace the damaged connector.
- Reset the code after repair using a diagnostic tool.
Practical Tips
- Cleaning: A dirty sensor can distort readings → Use an electronic cleaner.
- Compatibility: Choose a sensor compatible with your Buick model.
- Post-repair verification: Test drive the vehicle to confirm the absence of symptoms.
For advanced diagnostics, consult a certified mechanic or a repair manual specific to your Buick.