Code
P1140
DAEWOO
P — Powertrain
INTAKE AIR TEMP. SENSOR
Views:
UK: 18
EN: 30
RU: 25
AI status
Completed
Completed
100%
Causes
- Open or short in IAT sensor wiring
- Loose, corroded or damaged sensor connector
- Failed IAT sensor (thermistor)
- Poor ground or lost reference voltage to sensor
- Contamination or physical damage to the sensor
- Intermittent connection due to vibration
Symptoms
- Check Engine Light (MIL) illuminated
- Incorrect intake air temperature reading on scan tool (extremely high/low or fixed value)
- Poor cold-start drivability or extended warm-up enrichment
- Reduced fuel economy and drivability issues
- Rough idle or hesitation
- Possible increased emissions
What to check
- Read and record freeze-frame and live IAT sensor data with a scan tool
- Visual inspection of IAT sensor, connector, and wiring for damage or corrosion
- Backprobe harness to confirm reference voltage (typically 5V) and ground presence with key ON
- Measure signal voltage at the connector and compare to ambient temperature
- Measure sensor resistance with sensor disconnected and compare to expected values
- Wiggle test harness while monitoring live data for intermittent faults
Signal parameters
- Typical reference voltage to sensor: ~5.0 V (varies by model)
- Typical signal voltage: ~0.3–4.7 V depending on temperature (lower voltage = colder or hotter depending on circuit design; verify service data)
- NTC thermistor behavior: resistance decreases as temperature rises
- Typical cold/ambient resistance example: ~2–10 kΩ at ~20–25°C (manufacturer-specific — consult service data)
- Open-circuit: very high/OL resistance or signal voltage at one extreme; short to ground: ~0 V; short to 5V: ~5 V
Diagnostic algorithm
- Retrieve DTC and freeze-frame data. Note the recorded IAT value and engine conditions.
- Perform a visual inspection of the intake air temp sensor and connector for corrosion, bent pins, oil/water contamination, or damage.
- With ignition ON (engine OFF), backprobe the sensor connector: verify reference voltage (≈5V), sensor ground, and measure sensor signal voltage. Record values.
- Unplug the sensor and measure its resistance at ambient temperature. Compare to the manufacturer's resistance vs temperature chart. If out of spec, replace the sensor.
- If resistance is OK but signal voltage is incorrect, check continuity between sensor connector pins and ECU pins. Repair any opens or shorts. Check for short to ground or 5V.
- Perform a dynamic test: warm or cool the sensor (hair dryer or freeze spray) while monitoring live data to confirm the signal changes smoothly and logically.
- Repair or replace wiring, connector, or sensor as required. After repairs, clear codes and perform a road test to verify the fault does not return.
- If all wiring and sensor tests pass but code persists, consider ECU input driver fault and test/replace ECU per manufacturer procedure.
Likely causes
- Broken wire in harness between sensor and ECU
- Pin pushed out or corroded at connector
- Sensor thermistor drifted out of spec or failed
- Short to ground or to 5V reference in harness
- Water or oil contamination on the sensor or connector
Fault status
Status
Intake Air Temperature Sensor Circuit — open/short/implausible signal detected
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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