Fuel and air

P0099 — Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

Severity: low Safe to drive

What P0099 means

The engine control module constantly reads the voltage from intake air temperature (IAT) sensor 2 and uses it to adjust fuel delivery and other settings. P0099 sets when that signal jumps around, drops out or does not match how air temperature really changes. It usually points to a poor connection or a failing sensor rather than serious engine damage.

Symptoms

  • Check Engine light on
  • Worse fuel economy
  • Hesitation or sluggish throttle response
  • Rough or unstable idle
  • Harder starting in very hot or cold weather

Possible causes

  1. Corroded, loose or damaged IAT sensor 2 connector
  2. Open, chafed or shorted wiring to the sensor
  3. Failed intake air temperature sensor 2
  4. Dirty air filter or cracked intake duct skewing readings
  5. Faulty mass air flow (MAF) sensor, if the IAT sensor is built into it
  6. Rarely, a PCM fault

How to diagnose

  1. Read freeze-frame data and check for other codes on the IAT, MAF or intake pressure sensors
  2. Watch live data: IAT 2 should change smoothly and match ambient temperature on a cold engine
  3. Inspect the connector and harness for moisture, corrosion, chafing or bent pins
  4. Wiggle the harness and connector with the engine running and watch for signal spikes
  5. Measure sensor resistance and compare it with the manufacturer's temperature chart
  6. Test the signal and ground wires back to the PCM for opens and shorts, and check the reference voltage
  7. Inspect the air filter and intake ducts for cracks or air leaks
  8. Clear the code after repair and confirm it does not return

Common fixes

  • Clean the connector terminals or replace the connector
  • Repair or replace damaged wiring
  • Replace intake air temperature sensor 2
  • Replace the MAF sensor if it is the source of the fault
  • Replace a dirty air filter or cracked intake duct

Questions and answers

What does P0099 mean?

It means the signal from the second intake air temperature sensor is intermittent or erratic. The PCM cannot trust the air temperature data.

Can I drive with P0099?

Usually yes, though you may notice worse fuel economy and weaker performance. Get it checked soon.

How do I fix P0099?

Start by inspecting the sensor connector and wiring, then test the sensor itself. Cleaning the contacts or replacing the sensor often solves it.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.