A system can include an engine, an aftertreatment system with a particulate filter, and a controller. The controller is configured to compare a time value since a last delta pressure soot load estimate process to a predetermined time threshold. Responsive to the time value being greater than or equal to the predetermined time threshold, the controller decreases a flow threshold value to a lower flow threshold value. If the flow amount is greater than or equal to the lower flow threshold value, then the controller activates a delta pressure soot load estimation process. A combined soot load estimate is then calculated using a delta pressure soot load estimation of the delta pressure soot load estimate process responsive to the lower flow threshold value.