Degraded Aftertreatment Systems Costing Fleets $30 per Truck Daily in Wasted Fuel

A mixed-class fleet analysis by Questar revealed that mechanically degraded aftertreatment systems are costing fleets as much as $30 per vehicle per day in excess fuel consumption, according to findings published in the white paper The Hidden Fuel Cost of Mechanical Degradation. Clogged diesel particulate filters create exhaust backpressure that forces engines to work harder and burn more fuel to expel combustion gases. Degraded selective catalytic reduction systems trigger frequent active regeneration cycles that waste additional fuel while burning off soot. Questar's analysis found that excess fuel burned in vehicles operating with these degraded systems averaged $27 per vehicle per day, with some vehicles wasting as much as $25 to $30 daily. In one case, a fleet vehicle showed 0.13 gallons per hour wasted during idling, representing over 10% waste. Questar's AI-driven platform continuously collects vehicle data from telematics signals and diagnostic trouble codes, running machine learning models to produce health scores for major vehicle systems. The platform's autonomous research agent examined thousands of vehicle-days and hundreds of sensor parameters to build predictive models of fuel consumption. By comparing predicted consumption against actual consumption and accounting for driving conditions and vehicle type, the analysis quantified how aftertreatment system degradation directly correlates to increased fuel burn. For fleet managers, the findings underscore the financial importance of keeping aftertreatment systems maintained. Persistent trouble codes tied to these systems signal not just compliance and maintenance costs, but measurable daily losses in fuel economy across the entire operation.