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P1109

IAT B Sensor Intermittent.

  • Lincoln
  • Powertrain
  • Manufacturer code
  • Low severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
1
AreaFuel and air metering
09
FaultThe specific fault in that area

What it means

On Lincoln models, P1109 means the powertrain control module has detected an intermittent fault in the Intake Air Temperature (IAT) B sensor circuit. The signal from the sensor has briefly dropped out, jumped or gone implausible rather than failing outright. Which sensor is 'B' and where it sits depends on the model and engine.

Symptoms

  • Check engine light on
  • Intermittent rough running or hesitation
  • Slightly poor fuel economy
  • Occasional hard starting, especially when hot or cold
  • Fault that comes and goes, sometimes clearing itself

Possible causes

  • Loose, corroded or damaged connector at the IAT B sensorlikely
  • Chafed, broken or intermittently open/shorted wiring between the sensor and the PCMlikely
  • Failing IAT B sensor with an intermittent internal faultlikely
  • Heat, vibration or moisture affecting the sensor or harness near the intake or charge air pathpossible
  • Poor sensor reference or ground connection shared with other sensorspossible
  • Internal PCM fault or outdated software, where the manufacturer has documented it for that modelrare

How to diagnose

  1. Read all stored and pending codes and record the freeze frame data, noting engine temperature, load and intake air temperature when the code set.
  2. Check for related codes for other IAT sensors, MAF or reference voltage faults, which could point to a shared wiring or ground problem.
  3. Find the IAT B sensor using the model-specific wiring information, then inspect the sensor, connector and harness for damage, corrosion, moisture, rubbing or heat damage.
  4. With the engine at running temperature, watch the live IAT B reading and wiggle the connector and harness; look for spikes, dropouts or readings that do not follow the other IAT reading.
  5. Compare the IAT B reading with the other intake temperature readings and ambient temperature on a cold engine; they should be close.
  6. Check the sensor's resistance against the manufacturer's temperature table and check the reference voltage and ground at the connector.
  7. Test the wiring for continuity and short circuits between the sensor and the PCM, with the battery disconnected as required.
  8. Check whether any manufacturer software updates or technical bulletins apply to your model and engine.

How to fix

  • Clean, repair or replace the corroded or loose connector terminals.
  • Repair or replace the damaged section of wiring, and secure it away from heat and abrasion.
  • Replace the IAT B sensor if its readings drop out or do not match its temperature table.
  • Restore a poor reference or ground connection found during testing.
  • Apply a PCM software update only if a documented fault for your model calls for it, then clear the code and road test to confirm.

Can I keep driving?

Low severity

The car can normally be driven while you arrange a repair, as the PCM will substitute a default temperature value. Book it in soon if you notice hesitation, rough running or hard starting.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

This code for other makes

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