Function Explanation (DTC Detection Outline)

• The PCM performs diagnosis of the EGR system by comparing the target EGR volume with the actual.
• The PCM monitors the flow volume during EGR implementation.
• The PCM calculates the difference between the target EGR flow volume and the actual EGR flow volume during EGR implementation. If the monitored, actual flow volume is lower than the specification for the target flow volume, the PCM determines that there is inadequate flow volume.
• The PCM performs diagnosis when each of the preconditions during drive cycle is met. If a malfunction is detected, the malfunction detection counter begins counting up. The value of the malfunction detection counter is maintained while the preconditions are not being met. If the cumulative value of the malfunction detection counter exceeds the threshold during the first drive cycle, a malfunction is determined and a pending code is stored.
• If the calculated value of the malfunction detection counter during one drive cycle exceeds the threshold, the PCM determines a malfunction, stores a DTC and turns on the check engine light.

Fig 1: Flow Volume During EGR Implementation Cycle Graph

Courtesy of MAZDA MOTORS CORP.