Code
P1111
CHEVROLET
P — Powertrain
Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
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EN: 54
RU: 64
AI status
Completed
Completed
100%
Causes
- Open or broken wiring in IAT circuit
- Short to battery voltage or to the 5V reference
- Poor or corroded connector pin contact
- Failed IAT sensor (thermistor) internally open or out of specification
- Intermittent ground or poor chassis/ECM ground
- Intermittent PCM/input driver fault
Symptoms
- Illuminated MIL (check engine light)
- Incorrect intake air temperature readings on scan tool (very cold or erratic values)
- Hard starting or poor cold idle behavior
- Reduced engine performance, rough idle or hesitations under some conditions
- Possible increased fuel consumption if PCM uses wrong IAT data
What to check
- Retrieve stored freeze-frame and pending codes; check DTC freeze data and occurrence pattern
- Monitor live IAT sensor voltage and calculated temperature with scan tool while key ON and during engine warm-up
- Compare IAT reading to ambient air temperature and coolant temperature for plausibility
- Inspect IAT sensor connector for corrosion, bent pins, or water intrusion
- Perform a wiggle test on harness and connector while monitoring IAT voltage for intermittent change
- Check for proper reference voltage (usually ~5V) at the harness connector and a good ground
Signal parameters
- Typical IAT circuit voltage range (generic): ~0.1 V to ~4.8 V depending on inlet air temp (cold ≈ higher voltage, warm ≈ lower voltage)
- Expected reference voltage to sensor: ~5 V (verify exact value for vehicle)
- Open-circuit/short condition: voltage stuck near reference (high) or near 0 V (low)
- Typical resistance behavior (NTC): high resistance at cold, low resistance at hot — exact ohms vary by sensor and temp (consult spec)
Diagnostic algorithm
- Confirm code and whether it is intermittent: check freeze frame and run data for re-occurrence conditions.
- With ignition ON (engine OFF), backprobe the IAT signal wire and record voltage. If voltage is near reference (high) intermittently, suspect open/short to Vref or sensor open.
- Check for stable 5V reference at the connector and check ground continuity between sensor ground circuit and chassis/ECM ground.
- Inspect connector and wiring for corrosion, bent pins, broken strands, heat damage, or water entry. Repair or clean as needed.
- Remove sensor and measure sensor resistance with a multimeter at ambient temperature. Compare to typical thermistor curve or known-good sensor values. Replace if out of spec.
- Perform wiggle test on harness and while moving harness observe live voltage for intermittent spikes. Repair wiring faults found (splice, replace harness section).
- If wiring and sensor test good, check for short to battery/5V by isolating the harness and measuring voltage with sensor disconnected. If still present, trace for short to power.
- If intermittent high voltage persists after sensor and harness repairs, consider ECM input driver fault and test/replace ECM per service manual procedures.
- Clear codes and perform road/test cycles to confirm the fault does not return.
Likely causes
- Corroded/loose IAT connector or pinned terminal
- Wiring chafe causing intermittent short to 12V or 5V
- Sensor failure (open or erratic thermistor)
- Damaged insulation allowing intermittent contact with power
- Poor engine/ECM ground causing voltage spikes
Fault status
Status
P1111 — IAT sensor circuit intermittent high voltage detected. PCM saw voltage above expected range on the intake air temperature input intermittently; may cause incorrect air temperature readings and driveability effects.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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