Fleet DPF Maintenance: A Plan for Van and Car Fleets

Most advice about diesel particulate filters is written for the driver: take it for a long run, don’t ignore the warning light. That is fine for one car. It falls apart when you run twenty vans on multi-drop routes and none of your drivers chooses where they go. Fleet DPF maintenance is a planning job, and it belongs with whoever books the vehicles off the road.

Why fleet DPF maintenance is a scheduling problem

A DPF traps soot and burns it off during regeneration. That only works when the exhaust gets hot enough for long enough. Short hops, stop-start town work and long spells of idling all cut regenerations short, so the filter loads up faster than it clears.

On a private car the fix is often a change of driving habit. On a fleet you can’t rebuild a delivery route around a filter. The vehicles that block most often are usually doing exactly the work you need them to do. So rather than asking drivers to change how they drive, the plan has to work around how the vehicles are actually used.

There is a second reason regenerations alone won’t keep a fleet clear. Soot burns, but ash doesn’t. DieselNet’s technical summary describes DPF ash as the incombustible material left behind following filter regeneration and soot oxidation, mostly from lubricant additives. It builds up mile after mile on every vehicle, however well it is driven. On a high-mileage van that has only ever been regenerated, a lot of what blocks the filter is ash.

Step 1: Group your vehicles by duty cycle

Not every vehicle needs the same attention. Start by sorting the fleet into a few groups based on what each one does day to day. This tells you where to look first.

Your first group is where most unplanned downtime comes from. If you only have time to watch some of the fleet closely, watch those vehicles.

Step 2: Decide what triggers a clean

A plan needs clear rules for when a vehicle gets booked in. Waiting for limp mode means the vehicle decides when it comes off the road, usually halfway through a job. These are the triggers we suggest fleets use:

• A DPF warning light that comes back. One light that clears after a good run is normal. A light that returns within days is not. Our guide to what each DPF warning stage means helps your team tell the two apart.
• Regenerations getting more frequent. If your telematics or a diagnostic check shows regens coming round far more often than they used to, the filter is losing capacity.
• Power or fuel complaints from the driver. Drivers notice before dashboards do. Make it easy for them to report it.
• High mileage on a filter that has never been cleaned. Ash load grows with use. A filter that has only ever been regenerated is a candidate for an inspection even before it causes a problem.
• A failed forced regeneration. If a regen at the workshop doesn’t bring the readings down, the filter needs cleaning off the vehicle.

Step 3: Keep a DPF record for every vehicle

The single most useful thing a fleet can do is write it down. A short record per vehicle turns guesswork into a pattern you can plan around. Over a few months it shows which vehicles, drivers and routes block filters fastest.

Heavy goods and bus operators already work this way. DVSA’s guide to maintaining roadworthiness says records of safety inspections must be kept for at least 15 months for those vehicles. It also notes that its general principles could equally apply to light goods vehicles below the operator licensing thresholds. Van and car fleets aren’t bound by that rule, but it is a sensible model to borrow. The same guide recommends a planner or wall chart showing inspection dates at least six months ahead, and DPF checks slot straight into that kind of plan.

Step 4: Book the clean when it suits you

Once a vehicle hits a trigger, the aim is to get it cleaned at a time you choose. That is where off-vehicle cleaning helps fleets. Your workshop or fitter takes the filter off, it comes to us, and we clean it in our machine at our Fenton workshop.

Dirty water draining from a filter during a clean in our current machine at the Fenton workshop.

There are three ways to get the work done:

Every filter is checked for cracks, a melted core or housing damage before cleaning, and tested before and after so you have readings for the vehicle’s record. Our fleet DPF cleaning service sets out how we fit the work around vehicles that need to stay earning.

If your fleet keeps a spare filter for its most common model, a removed unit can be cleaned while the spare is fitted. That turns a filter swap into a short workshop job rather than a day off the road.

Step 5: Fix the cause, not just the filter

If the same vehicle keeps coming back, the filter is usually telling you about something else. A sticking EGR valve, a faulty sensor, worn injectors or oil getting into the exhaust will all load a DPF faster than normal. Cleaning restores the filter, but it won’t stop the problem coming back.

Your records are what spot this. A vehicle whose cleans come round much sooner than similar vehicles on similar work needs a closer look upstream. Our guide to engine problems that keep blocking a DPF covers the usual suspects. Using the oil grade the manufacturer specifies matters too, because ash comes mainly from oil additives.

The DPF and the MOT

A blocked filter isn’t just a downtime problem. Since May 2018 the MOT has been stricter on diesels with a DPF. Under the MOT rule changes, a vehicle gets a major fault if the tester can see smoke of any colour coming from the exhaust, or finds evidence that the DPF has been tampered with.

For vans, our article on whether a blocked DPF can fail an MOT goes into more detail.

Frequently asked questions