Speed Density

On models equipped with MAP and MAT sensors, the speed density is used to compute the airflow rate. Manifold pressure and temperature are used to calculate the airflow rate to the ECM. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes.

The ECM sends a volt signal to the MAP sensor. Manifold pressure changes result in resistance changes of MAP sensor. By monitoring MAP sensor output voltage, the ECM determines manifold pressure. If MAP sensor fails, the ECM will apply a fixed MAP value and use the TPS to control fuel.