Code
P1190
SCION
P — Powertrain
Intake air temperature sensor circuit
Views:
UK: 1
EN: 1
RU: 6
AI status
Completed
Completed
100%
Causes
- Faulty intake air temperature (IAT) sensor (NTC thermistor)
- Open or shorted wiring between IAT sensor and ECM
- Corroded, bent, or loose connector terminals at the sensor or ECM
- Intake air sensor contaminated by oil/dirt or physically damaged
- Faulty ECM/PCM or poor ground/5V reference supply
- Aftermarket or incorrect replacement sensor (wrong specification)
Symptoms
- Illuminated Check Engine Light (MIL) with P1190 stored
- Incorrect intake air temperature reading on scan tool (stuck, pegged high/low, or erratic)
- Poor cold-start driveability (rich/lean mixture) or rough idle
- Reduced fuel economy and possible hesitation or reduced power
- Difficulty achieving correct engine warm-up or extended open-loop operation
What to check
- Retrieve freeze frame and live data with an OBD-II scanner; note IAT reading and related parameters (MAF, fuel trims, coolant temp)
- Visually inspect IAT sensor, connector, and wiring for corrosion, broken pins, melted insulation, or contamination
- Backprobe sensor connector and measure signal voltage with ignition ON and engine OFF, then while running
- Measure sensor resistance at the harness unplugged and compare to ambient temperature expected value
- Check for 5V reference and sensor ground at the connector (key ON)
- Perform wiggle test of harness while monitoring live IAT signal for intermittent behavior
Signal parameters
- Typical IAT sensor behavior (NTC thermistor): resistance decreases as temperature increases
- Approximate resistance examples (varies by sensor): ~8–10 kΩ at 0°C, ~2–3 kΩ at 20–25°C, ~200–400 Ω at 80°C (use OEM chart when available)
- Typical signal voltage range: ~0.2–4.8 V depending on air temperature and vehicle wiring; at ambient (~20°C) expect midrange voltage (~1.0–2.5 V) on many systems
- Reference supply: 5.0 V nominal from ECM, and a reliable ground required for correct readings
Diagnostic algorithm
- Connect a scan tool, record freeze frame and live IAT values, and confirm P1190 is current; note related codes (MAF, coolant temp, fuel trims).
- Visually inspect sensor and harness for obvious damage, corrosion, or contamination; repair as needed.
- With connector disconnected, measure sensor resistance at ambient temperature and compare to expected curve or OEM spec. Replace sensor if out of range.
- Reconnect and backprobe connector: verify ECM 5V reference present on supply terminal (key ON), check ground continuity to chassis, and measure signal voltage. Confirm readings change with ambient temperature (hold sensor in hand or use ice/warm air carefully).
- If signal is stuck high/low or erratic, check wiring continuity between sensor and ECM for open or short to 12V/ground; repair any damaged wiring or connector terminals.
- Perform wiggle test while monitoring live data to find intermittent faults; repair or replace harness/connector as necessary.
- If wiring and sensor test good, test ECM input circuit per factory procedure or substitute known-good ECM if indicated.
- Clear codes and verify repair by test drive and confirming IAT values and no return of P1190.
Likely causes
- Damaged or corroded sensor connector/wiring (most common)
- Failed IAT sensor element (thermistor drift/open)
- Short to power or ground in harness (pinched/damaged wiring)
- Intermittent connection due to vibration or water intrusion
- Rare: ECM input circuit fault or loss of 5V reference
Fault status
Status
ECM detected a malfunction in the intake air temperature sensor circuit (open, short, intermittent, or out‑of‑range signal).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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