Code
P1111
HUMMER
P — Powertrain
Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
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UK: 18
EN: 32
RU: 44
AI status
Completed
Completed
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Causes
- Faulty IAT sensor (thermistor) producing high/open-circuit voltage
- Intermittent short to battery/5V reference on the IAT signal wire
- Poor or intermittent ground for the sensor circuit
- Corroded, loose, or damaged sensor connector or pins
- Damaged wiring harness (chafing, broken strands, intermittent contact)
- Faulty PCM input circuit (less common)
Symptoms
- Check Engine Light (CEL)/Malfunction Indicator Lamp (MIL) illuminated
- Erratic idle or stumble under some conditions (if PCM uses IAT for fueling/ignition)
- Possible poor fuel economy or hesitation
- Engine may run rich or lean depending on how PCM interprets the faulty signal
- Intermittent occurrence — may not reproduce consistently
What to check
- Read freeze frame and live data to see when the fault sets and correlate with engine temp/conditions
- Visually inspect IAT sensor connector and wiring for corrosion, bent pins, or damage
- Wiggle harness and connector while monitoring live IAT voltage to reproduce the fault
- Verify battery and charging system voltage is within normal range
- Check for aftermarket accessories or recent repairs that could affect wiring
- Scan for any other related DTCs (MAP, MAF, engine temp) that might point to shared wiring/grounds
Signal parameters
- IAT sensor is typically an NTC thermistor returning a voltage to the PCM in the 0.2–4.8 V range
- Voltage normally decreases as intake air temperature rises (higher voltage at cold temps, lower at hot)
- Typical bench/reference value: ≈2.5 V at ~25 °C (varies by sensor design and vehicle)
- Open-circuit or short-to-voltage will produce voltages near 0 V or near battery/5 V respectively
- PCM reference supply usually ~5 V; IAT signal should not exceed that reference
Diagnostic algorithm
- Retrieve codes and freeze-frame data. Note engine temperature and operating conditions when P1111 set.
- Visually inspect the IAT sensor, connector and wiring for corrosion, damage, loose pins, or aftermarket splices.
- Backprobe the IAT connector and monitor live voltage with a DVOM or scan tool while engine is cold and warming. Expect ~0.2–4.8 V and smooth change with temperature.
- Wiggle the harness and connector while watching the signal for intermittent spikes or dropouts to reproduce the fault.
- Check for short to battery/5 V: with key ON (engine off) measure IAT signal; if it is at or near battery/5 V, suspect short to power or failed sensor output.
- Check for open/ground issues: measure resistance from IAT signal to PCM input and check ground continuity to chassis; inspect connector pin integrity.
- Measure sensor resistance (unplugged) at known temperatures and compare to expected thermistor behavior (resistance should change with temperature).
- Verify PCM 5 V reference and sensor ground circuits are stable and not intermittent. Repair poor grounds or reference wiring as needed.
- If wiring and connectors test OK but signal still intermittent, replace the IAT sensor and retest.
- If problem persists after replacing sensor and repairing wiring, test/replace PCM only after verifying all inputs/grounds and consulting service manual diagnostics.
Likely causes
- Loose/corroded connector or poor contact at the IAT sensor
- Intermittent short to voltage on the IAT signal wire (pinched or rubbed through insulation)
- Failing IAT sensor with intermittent open/high output
- Intermittent ground or poor reference voltage from PCM
Fault status
Status
Intermittent high voltage detected on Intake Air Temperature (IAT) sensor circuit. Inspect sensor, connector, and wiring for intermittent short/poor contact.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Repair manuals
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