P0099 Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

P0099 indicates intake air temperature sensor 2 is intermittent or erratic. The signal drops out, spikes, or changes too abruptly.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace unrelated intake parts without reproducing the IAT2 signal dropout or erratic movement.

Symptoms of P0099

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0099

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Graph IAT2 data while moving the intake harness, driving over vibration, warming the engine, and repeating freeze-frame conditions.
Inspect connector locking, terminal tension, water intrusion, sensor contamination, harness rub points, and intermittent ground or reference faults.
Compare sudden IAT2 changes with sensor 1, ambient temperature, boost events, and related airflow or pressure codes.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.