DPF warning on a winter city circuit
A Euro VI city bus operates a 9 km loop with 22 stops in Skopje. In February, the driver notices the diesel particulate filter (DPF) warning lamp and a message 'exhaust filter regeneration required'. The bus has 38 passengers. The outside temperature is 2 °C, and the driver has been idling at the terminus for 20 minutes each hour to keep the cabin warm. The route never exceeds 40 km/h, and the bus makes frequent short trips. Fuel consumption has risen from 28 L/100 km to 34 L/100 km over two weeks. AdBlue level is 18%. The next scheduled service is in 600 km. The driver has 15 minutes of layover at the terminus. The operator's policy says regeneration should be done at highway speed for 20–30 minutes. The dashboard also shows a yellow engine symbol. The bus is due back at the depot in 3 hours.
1. Explain why the DPF warning and higher fuel consumption are linked, and what immediate risks exist if ignored.
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The DPF traps soot from the exhaust. It burns off stored soot only when exhaust temperature is high enough, which usually requires sustained higher-speed driving. This route is a 9 km loop at up to 40 km/h with 22 stops, plus 20 minutes of idling each hour at the terminus. That pattern keeps exhaust temperatures low and adds soot, so the filter accumulates more than it can burn off. Backpressure rises, the engine works harder, and fuel consumption increases from 28 to 34 L/100 km. Idling also burns fuel without moving the bus and increases local emissions. If ignored, the warning can progress to a red lamp, reduced engine power, a forced workshop regeneration, or a blocked filter that stops the bus with passengers on board. AdBlue at 18% is not the immediate cause, but it should be monitored. The yellow engine symbol suggests the fault is already stored.
2. What should the driver do on this shift, given the 15-minute layover and passenger load?
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The driver should not ignore the warning or simply continue the loop. A 15-minute layover is not enough for a 20–30 minute highway regeneration. The driver should inform dispatch immediately and ask for a serviceable replacement bus or a route that allows regeneration, such as a run at 60–80 km/h for the required time. If the operator authorizes a regeneration run, it must be done according to the manufacturer's instructions and not while passengers are on board unless the procedure permits it. The driver should stop idling for cabin heat: use the auxiliary heater if fitted, or limit idling to the minimum needed for defrosting and comfort. If the DPF lamp turns red or the engine derates, the driver must stop safely and not continue in service. The bus should go to the workshop within the 600 km service window if regeneration cannot be completed. Passengers should be kept informed of any delay.
3. List eco-driving techniques for this route that reduce fuel and emissions without compromising schedule.
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Eco-driving on this loop means smooth acceleration and early lift-off, anticipating red lights and stopped buses instead of braking late. Use the retarder or engine brake rather than harsh service braking. Keep tyre pressures at specification; soft tyres increase rolling resistance. Avoid unnecessary idling: at the terminus, switch off the engine if the auxiliary heater can maintain comfort, and restart only when needed. Use ECO mode if the bus has it, and avoid jack-rabbit starts. Reduce electrical load where possible, but do not compromise demisting or lighting. Keep the bus clean and remove unnecessary weight. Follow the timetable without racing: harsh acceleration to recover time burns more fuel. Report the DPF issue so maintenance can check the filter and injectors. These measures cut fuel and emissions, but they do not replace the required regeneration; they reduce the rate of soot build-up.