04/12/2014
What To Do If Your DPF Is Blocked
In today’s world of ever-tightening emissions regulations, Diesel Particulate Filters (DPFs) have become commonplace to help keep those dirty diesels rolling off the production line. Without them, many diesel engines would have been retired in the light of Euro 5 & 6 emissions standards. DPFs may well be great for the environment, but the cost of DPF regenerations, repairs, and replacement can run up eye-watering bills – a lesson many of us have learnt first-hand! So, what can you do to keep your DPF filter trouble-free and your wallet intact? Here’s our comprehensive guide to keeping your DPF clean and trouble-free.
Understanding the Diesel Particulate Filter (DPF)
A Diesel Particulate Filter (DPF) is an exhaust after-treatment device designed to remove particulate matter (soot) from the exhaust gases of a diesel engine. It works by trapping the soot in a filter structure. Over time, this trapped soot can build up and potentially block the filter. To combat this, the engine's management system initiates a process called 'regeneration'.
DPF Regeneration Explained
Regeneration is the process of burning off the trapped soot within the DPF, converting it into a small amount of ash. There are two main types of regeneration:
- Passive Regeneration: This occurs automatically during normal driving when exhaust gas temperatures are high enough (typically above 250-300°C). This often happens during longer journeys at consistent speeds.
- Active Regeneration: This is initiated by the engine control unit (ECU) when it detects that the DPF is becoming too full of soot. The ECU injects a small amount of fuel into the exhaust system to raise the exhaust gas temperature, burning off the trapped soot. This often happens during driving, but may require specific conditions to be met.
Common Causes of a Blocked DPF
Several factors can contribute to a blocked DPF, often related to driving style and vehicle maintenance:
- Short, Frequent Journeys: Urban driving with frequent stops and starts, and low speeds, often prevents the exhaust system from reaching the temperatures required for passive or active regeneration. This leads to soot accumulation.
- Incorrect Engine Oil: Using engine oil that is not approved by the manufacturer, particularly oil with high levels of sulphated ash, can clog the DPF.
- Faulty EGR Valve: A malfunctioning Exhaust Gas Recirculation (EGR) valve can lead to increased soot production, overwhelming the DPF.
- Ignored Warning Lights: Failure to address DPF warning lights promptly can lead to more severe blockages.
- Engine Misfires or Turbo Issues: Problems with the engine's combustion or turbocharger can lead to excessive soot being produced.
Your Top Tips for a Trouble-Free DPF
Drive Faster (Sometimes!)
Contrary to popular belief, driving faster could actually save you money in the long run. DPF regenerations can only occur when certain conditions are met, such as sustained speed, RPM, and engine temperature. Unless all these conditions are met, the DPF regeneration process will not start, and you’ll be one step closer to a costly dealer regeneration. Do your homework; find out how fast you need to drive, for how long, and at what RPM. Your dealer might not want to give you this information, so we’d recommend reaching out to the online community and owners’ clubs for this. A good rule of thumb is to aim for a sustained period of driving at motorway speeds (e.g., 50-70 mph) for at least 20-30 minutes, ideally once a month, if your typical journeys are short.
Use the Right Oil
Choosing the right oil for your car is vital to ensuring your engine produces as little diesel particulate matter as possible. Always try and use the manufacturer-approved engine oil. Most manufacturers specify a low SAPS (Sulphated Ash, Phosphorus, and Sulphur) oil, which is specifically designed to be low in sulphated ash. This is a by-product of diesel combustion that causes the DPF “mesh” to become blocked over time. Using the correct oil is a proactive step that significantly reduces the risk of premature DPF clogging.
SAPS Levels Explained:
Oil Type Sulphated Ash Content Suitability for DPFs Standard/High SAPS High Not Recommended Mid SAPS Medium May be suitable, check manufacturer guidance Low SAPS (e.g., ACEA C3, C4) Low Recommended Get Your EGR Valve Checked
Over time, EGR valves can become blocked with the soot and carbon they are designed to recirculate. This, in turn, can cause the device to stick open or open for longer than it should, increasing the amount of particulates, soot, and carbon fed back into the engine. A faulty EGR valve should illuminate the engine warning light, but if you have experienced DPF issues in the past, we’d suggest having it looked at before any further costly DPF regenerations. Cleaning or replacing a faulty EGR valve can often resolve related DPF problems and improve overall engine performance.
Keep Out of Town (When Possible)
The start-stop nature of urban driving is one of the biggest reasons many drivers experience DPF issues. Short distances, low speeds, and the stop-start nature of driving in built-up areas can make it near impossible to replicate the conditions needed for an active or passive DPF regeneration. Try and mix in some faster, less congested roads to maximise the chance of a regeneration (as mentioned in tip 1). If your daily commute consists solely of short trips, consider incorporating a longer, faster drive into your routine, perhaps on a weekend.
Buy the Right Car!
My rather unpleasant and expensive experience with the DPF in my 2.0dci Nissan Qashqai seemed to hit a chord with my fellow “Urban Proof” owners. Qashqai owners’ clubs were rife with the very same issue again and again, suggesting that some marques are more susceptible to DPF issues than others. Before you start looking for your next oil burner, we’d suggest doing some digging and asking in many online owners’ clubs and forums for their experiences. Taking into account your driving habits, it may well be better to opt for another model or even the petrol-powered alternative if your driving is predominantly short trips.
Get Clued Up!
OK, I know I said top five, but if you’ve found this page, then you’ve already either experienced issues or are having DPF issues. You’re in good hands, so why not check out our other DPF resources and get clued up? We’d suggest you take a look at the following pages for more in-depth information.
What to Do If Your DPF Is Already Blocked
If your DPF warning light has illuminated, or you’re experiencing symptoms like reduced engine power, increased fuel consumption, or a burning smell, your DPF may be blocked. Here’s what you should do:
1. Check for Warning Lights
Most modern cars will display a specific DPF warning light on the dashboard. If this light comes on, consult your owner’s manual. It will usually advise you to drive at a steady speed (around 40-50 mph) for about 10-15 minutes to encourage a regeneration. Do not ignore this light!
2. Attempt a Forced Regeneration (If Safe)
If the warning light appears, and it’s safe to do so, try to find a suitable stretch of road to drive at a consistent speed. If the light persists after this, or if it flashes, you may need a professional to perform a forced regeneration using diagnostic equipment.
3. Consider a Professional DPF Clean
If driving or a forced regeneration doesn’t clear the blockage, a professional DPF cleaning service might be the solution. These services often use specialised cleaning fluids and equipment to remove stubborn soot and ash deposits without removing the DPF from the vehicle. This is generally less expensive than a full replacement.
4. Professional Diagnosis and Repair
If cleaning doesn't work, or if there are underlying issues (like a faulty sensor, EGR valve, or injector), a qualified mechanic will need to diagnose the problem. They can check the DPF's backpressure, sensor readings, and the overall health of the exhaust system.
5. DPF Replacement (Last Resort)
In cases of severe blockage or damage, the DPF may need to be replaced. This is typically the most expensive option. It's crucial to ensure the replacement DPF is compatible with your vehicle and meets emissions standards. After replacement, it’s vital to address the root cause of the blockage to prevent premature failure of the new unit.
DPF Cleaner Additives
You might see various DPF cleaner additives available on the market. These are typically poured into the fuel tank and are designed to help reduce the combustion temperature of soot, making it easier for the DPF to regenerate. While some users report positive results, their effectiveness can vary, and they are generally considered a preventative measure or a mild aid rather than a solution for a heavily blocked DPF. Always choose a reputable brand and follow the instructions carefully.
Frequently Asked Questions (FAQs)
Q1: How do I know if my DPF is blocked?
Common symptoms include a DPF warning light on the dashboard, a noticeable loss of engine power, increased fuel consumption, and sometimes a burning smell from the exhaust. You might also notice the engine running rougher than usual.
Q2: Can I drive with a blocked DPF?
Driving with a blocked DPF is not recommended. It can lead to significant damage to the engine and exhaust system, potentially resulting in very expensive repairs. The engine’s performance will also be severely compromised.
Q3: How much does it cost to fix a blocked DPF?
Costs vary widely. A professional DPF clean might range from £150-£300. A forced regeneration by a mechanic could be less. However, DPF replacement can cost anywhere from £500 to £2,000 or more, depending on the vehicle make and model.
Q4: Will removing the DPF solve the problem?
While removing the DPF might seem like a solution to avoid future costs, it is illegal in most countries and can lead to hefty fines and your vehicle failing its MOT or emissions test. It also has environmental consequences.
Q5: How often should I drive on the motorway to help my DPF?
If your typical driving is short urban trips, aim for a longer drive (at least 20-30 minutes) at motorway speeds (50-70 mph) at least once a month. This provides the best chance for a passive or active regeneration to occur.
Your Feedback Matters
We’d love to hear your tips for keeping your DPF in check. Feel free to leave a comment below and share your experiences!
If you want to read more articles similar to Blocked DPF? Your Essential Guide, you can visit the Maintenance category.