About Component Monitors

There are several components that will affect vehicle emissions if they malfunction. If one of these components malfunctions the Malfunction Indicator Lamp (Check Engine) will illuminate.

Some of the component monitors are checking for proper operation of the part. Electrically operated components now have input (rationality) and output (functionality) checks. Previously, a component like the MAP sensor was checked by the PCM for an open or shorted circuit. If one of these conditions occurred, a DTC was set. Now there is a check to ensure that the component is in fact working. This is done by watching for a sensor change over a given time period. In the case of the MAP sensor, if the reading does change after idling for 2 seconds a DTC will be set.