Circuit Description

The Powertrain Control Module (PCM) uses the following information to calculate an expected airflow rate:

• The throttle position
• The barometric pressure (BARO)
• The manifold absolute pressure (MAP)
• The intake air temperature (IAT)
• The mass air flow (MAF)
• The engine speed (RPM)

If the PCM detects the airflow rate is more than expected, DTC P0121 sets.