Code
P1112
CADILLAC
P — Powertrain
Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage
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UK: 25
EN: 39
RU: 42
AI status
Completed
Completed
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Causes
- Loose, corroded, or damaged IAT sensor connector or wiring
- Intermittent short to ground in the IAT wiring
- Poor or intermittent connection at the PCM
- Faulty IAT sensor (thermistor)
- Water intrusion or contamination at the sensor/connector
- PCM internal fault or poor grounding (less common)
Symptoms
- Check Engine Light (MIL) illuminated, intermittent
- Poor idle, hesitation or drivability complaints under some conditions
- Erratic air temperature readings on live data (very low values intermittently)
- Possible increased fuel consumption or rough running when the fault is active
- Sometimes no obvious drivability symptoms between fault events
What to check
- Retrieve freeze frame and live data for IAT voltage/temp during the fault
- Visually inspect IAT sensor, connector, and wiring for corrosion, damage, or moisture
- Backprobe the IAT signal wire at the sensor and at the PCM to compare voltages
- Perform wiggle test on wiring and connector while monitoring live data to provoke the fault
- Measure sensor resistance vs ambient temperature and compare to known thermistor behavior
- Check for shorts to ground or battery using a multimeter (continuity and voltage drop tests)
Signal parameters
- Typical IAT sensor is an NTC thermistor; resistance decreases as temperature rises
- Ambient (20°C / 68°F) thermistor resistance often in the approximate range 2k–3kΩ (varies by sensor)
- Expected voltage to PCM typically ~1.0–3.0 V depending on temperature and circuit design; consult OEM spec
- Open circuit often shows very high resistance (>50–100 kΩ) or voltage near reference rail depending on pull-up
- Short to ground will show near 0 V on signal; short to battery will show near battery voltage
- Operating temperature measurement range commonly -40°C to +125°C
Diagnostic algorithm
- Read and record freeze frame, pending codes, and IAT live data (voltage and temperature).
- Visually inspect the IAT sensor and connector; clean and reseal if contaminated.
- With key on engine off, backprobe the signal wire at the sensor and check voltage. Compare with PCM signal at the harness connector to identify wiring or PCM issue.
- Wiggle the sensor wiring and connector while monitoring live data to reproduce intermittent low voltage.
- Measure sensor resistance at known ambient temperature and compare to expected thermistor behavior. Replace sensor if out of range or intermittent.
- Check continuity between the IAT sensor signal and PCM pin; check for shorts to ground or battery.
- If wiring and sensor check good, swap with a known-good sensor (if available) or test with a bench reference resistor to verify PCM response.
- Inspect and test PCM ground(s) and power supply circuits. If wiring, sensor, and grounds are good and fault persists, consider PCM diagnosis or reflash per OEM guidance.
- Clear codes and perform road/drive cycle to verify repair and that P1112 does not return.
Likely causes
- Corroded or loose connector at the IAT sensor
- Frayed or chafed wiring contacting chassis ground or engine components
- Faulty IAT sensor element (open/low-resistance intermittency)
- Contamination (oil/water) in connector causing intermittent low readings
Fault status
Status
P1112: IAT sensor circuit intermittent low voltage — the PCM detected repeated episodes where the intake air temperature signal fell below the expected range. Inspect IAT sensor, wiring/connectors, and related PCM connections for intermittent shorts, opens, or contamination.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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