Theory of Operation

WARNING: This page is about a different car, the 2011 RAM Pickup. However, it is still accessible from the selected car via links, so may be relevant.

The Mass Air Flow Sensor is a frequency based device. A constant voltage is applied to a heated wire. This wire is positioned in the air stream and is heated by the electrical current that the voltage produces. As air flows across it, it cools down. The heated wire or film is a positive temperature coefficient (ptc) resistor. This means that it's resistance drops when it's temperature drops. The drop in resistance allows more current to flow through it in order to maintain the programmed temperature. This current is changed to a frequency which is sent to the Powertrain Control Module (PCM) and interpreted as air flow. Adjustments for air temperature and humidity are taken into consideration since they also affect the temperature of the heated wire or film. This monitor fails if the MAF correction factor is beyond it's calilbrated range. The PCM will turn on the MIL lamp immediately after this monitor runs and fails. The PCM will turn off the MIL lamp when the diagnostic runs and passes in four consecutive drive cycles.