Code
P1193
PLYMOUTH
P — Powertrain
Inlet Air Temp Circuit High
AI status
Completed
Completed
100%
Causes
- Open or high‑resistance wiring in the IAT sensor circuit
- Short to battery voltage or accessory voltage on the IAT signal wire
- Faulty inlet/intake air temperature (IAT) sensor (thermistor)
- Corroded, bent or damaged connector/terminals at the sensor
- Poor engine/chassis ground or reference voltage problem
- PCM/ECM internal fault (rare)
Symptoms
- Check Engine / MIL illuminated
- Poor idle quality or hesitation on cold start
- Hard starting in some conditions
- Reduced fuel economy or drivability faults
- Engine may run in default/backup fuel strategy (enriched or fixed timing)
What to check
- Read freeze frame and live IAT sensor data with a scan tool
- Visually inspect IAT sensor and harness for damage, heat or corrosion
- Backprobe the IAT signal and reference wires; check for proper reference voltage with key ON
- Measure signal voltage at sensor with key ON/engine OFF
- Check continuity and resistance of the IAT signal and ground wires to the PCM
- Measure IAT sensor resistance at ambient temperature and compare to OEM curve/spec
Signal parameters
- Reference voltage: typically ~5.0 V reference from the PCM (varies by vehicle)
- Signal range: approximately 0–5 V depending on temperature and circuit design
- Expected idle/ambient signal: commonly within ~0.5–3.5 V (vehicle/design dependent)
- High fault condition: signal near reference voltage (e.g., >4.5 V) or above manufacturer threshold
- IAT sensor type: usually an NTC thermistor (resistance decreases as temperature increases)
Diagnostic algorithm
- Retrieve codes and live data. Note IAT voltage/temperature reading and freeze frame conditions.
- Visually inspect the IAT sensor, connector and wiring for damage, corrosion, pin push‑outs or water entry.
- With key ON (engine OFF) backprobe the sensor: verify reference voltage present at the PCM feed and that the signal wire reads a high voltage. If reference missing, diagnose upstream circuit.
- Check continuity between the sensor ground and chassis ground/PCM ground. Repair any high resistance grounds.
- Measure sensor resistance at ambient temperature and compare to OEM resistance‑vs‑temperature chart. If open or out of range, replace sensor.
- If sensor resistance is correct but signal voltage is high, inspect wiring for a short to battery/ignition voltage. Repair short or open as required.
- If wiring and sensor are good, temporarily substitute a known‑good IAT sensor (or bench test the sensor) to confirm.
- After repairs, clear codes and road test while monitoring IAT readings to confirm proper operation and that code does not return.
- If all external checks pass and problem persists, consider PCM input circuit fault; verify with manufacturer procedures before replacing PCM.
Likely causes
- Open/disconnected sensor connector
- Broken or chafed signal wire shorted to 12 V
- Failed IAT sensor (stuck high or open)
- Corroded terminal or water intrusion at sensor connector
Fault status
Status
P1193 — Inlet Air Temp Circuit High. PCM detected an excessively high voltage or out‑of‑range signal from the inlet air temperature sensor circuit. The condition may cause the PCM to use default sensor input values and set the MIL.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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