Blocked DPF symptoms – The early warning signs

(Last Updated On: May 3, 2023)

A blocked DPF can be a diesel driver’s worst nightmare. Not only is a DPF very expensive to rectify, and it renders the car utterly useless if it needs repair.
Arming yourself with the knowledge of blocked DPF symptoms and what it does is excellent preventative maintenance. It’s also good general knowledge as we can assure you if you know someone with a diesel car, I’m sure they’ve heard of the elusive problems with a DPF.

DPF stands for Diesel particulate filter, a component in the vehicle’s exhaust system. Not only can a blocked DPF be incredibly expensive to repair, but a car with a blocked DPF also will not drive or start if it becomes too much. This article will explain more in detail and what you should look out for.

What does a DPF do?

A DPF is essentially a trap for capturing soot. Soot is a by-product of burning diesel in an engine. The DPFs job is to capture and store the soot until the DPF becomes hot enough that it burns the soot in a process called regeneration. All that then remains is ash which is absorbed back into the filter.

This process stops the big black clouds of diesel smoke you see coming out of older vehicles under acceleration. It also removes the diesel particulate matter from the exhaust gasses, which are harmful to the environment.

What are the blocked DPF symptoms?

The first symptom that generally appears when a DPF is starting to block is a warning indicator that the DPF needs regeneration. Don’t panic; this is something you do yourself. No special skills are required!

DPF regeneration is automatic when a vehicle is on the motorway traveling above 40+mph (64+ kph) for more than 30 minutes. There are no buttons to press or procedures to follow; just drive!

Take this as loose advice because all diesel vehicles have their own way of regenerating the Diesel Particulate Filter. They are all pretty similar in that they involve driving for a while.

Other blocked DPF symptoms to look for are:

-illuminated DPF warning light that won’t go away following regeneration.
-Vehicle has gone into limp mode – it won’t accelerate past 20mph ish and stutters under acceleration.
-Holding back under acceleration.
-an excess amount of smoke coming from the exhaust.
Strong smell of diesel in the cabin.
-Stop/Start function not operating.
-Increased fuel consumption.
-Struggle to start the engine.

A blocked DPF can have many different symptoms, and they aren’t limited to one fault in particular. Some of the faults above could be confused with another severe issue with the vehicle. So it’s not safe to assume that just because your car has one of the symptoms, the DPF is to blame.

If you discover any of the issues on the list, it is wise to get a professional mechanic to check them out. They will be able to confirm where the fault lies. Especially if a regeneration run hasn’t cured the problem.

Why does a DPF become blocked?

A DPF is no different from any other filter in that it can become blocked. The unfortunate thing here is that a DPF cannot be casually swapped out like an oil or air filter.

As we already discussed, the DPFs job is to catch and store soot to burn off. However, the soot is never burnt away if a DPF does not reach regeneration temperatures. This causes a store of soot to get bigger, which will cause the DPF light to illuminate. Regeneration doesn’t usually happen until the exhaust gas temperatures reach 600 degrees Celsius (1112 degrees Fahrenheit).

The most significant cause of a DPF becoming blocked is many short stop-and-start journeys. A quick trip to drop the kids off at school doesn’t get the vehicle to the correct operating temperatures.

How do you prevent a DPF from blocking

Preventative measures are the best form of protection against a blocked DPF and actually almost all other components in a vehicle just like an EGR valve. As you will later read a blocked DPF is not a cheap fix. However, a few quick cheap ways to prevent a blockage.

  1. Purchase a DPF fuel cleaner to be poured into the diesel tank. As you drive, this will help clean the DPF more efficiently. It only needs to be done now and again; depending on how much you drive, refer to the bottle of cleaner for further instructions.
  2. A long drive for 20 – 30 minutes weekly allows the vehicle to get entirely up to temperature and get the DPF burning off the soot. It will work even better if a DPF cleaner is poured into the fuel.

How do you fix a blocked DPF?

There are 3 ways to fix a blocked DPF:

  1. the home remedy of a regeneration drive, but if the blockage is too significant, it will be too late for this to work.
  2. A DPF cleaning service. Which involves removing the DPF, flushing, and cleaning the internals with chemicals.
  3. Replace the DPF. However, be prepared for an expensive repair bill.

Sometimes the only cure will be to replace the Diesel particulate filter. Unfortunately, that comes with owning a diesel car with components that can fail at any moment.

exhaust replacement

Can you drive with a blocked DPF?

Driving with a blocked DPF could cause costly terminal damage to the engine and other ancillaries. Aside from the fact that the vehicle will not operate correctly or barely drive once completely blocked. The car could go into limp mode or shut down completely, which would be very dangerous in the wrong situation.

Do you need a DPF?

Yes, you do need a DPF. In theory, you can remove a DPF the same way you can remove the catalytic converter from a petrol vehicle; however, this is illegal. Not only does it alter the car’s performance, but the vehicle also requires supporting modifications to suit, which will damage the car if not done correctly.

Suppose that it is illegal does not put you off removing the DPF. Firstly, the car insurance companies could decide not to pay if you were involved in an accident, as the vehicle is no longer road worthy.
Secondly, your vehicle will not pass an annual inspection such as an MOT and invalidate any warranty with the manufacturer.

Frequently asked questions

Can you remove your DPF? Yes, but it is illegal.
Can you fix a DPF yourself? Driving above 40mph for 30 minutes will perform regeneration in most vehicles.
How long does it take for a DPF to block? There is no set time frame as everybody’s driving style is different. However, many short journeys over a few months could trigger the warning indicator.

Bottom line

A DPF on a car is not something to be ignored and can result in a costly fix if ignored. A DPF can be cared for by driving for 30 minutes at above 40 mph every other week. They aren’t designed to fail; they require little love and attention, that is all. Now you know the blocked DPF symptoms and how to prevent an issue. If you put some of these practices in place regularly, you will be very unlucky if you have to worry about a DPF repair bill.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

2 thoughts on “Blocked DPF symptoms – The early warning signs”

  1. My Honda Civic 1.6 Dtec had to have it‘s DPF removed and sent away for a professional cleaning,I hope this does the trick,after 248,000 kilometers ,do you think U will get lucky?

    • Thanks for your comment. Having the DPF professionally cleaned is very successful. If it has lasted 248,000 kilometers its done well, let’s hope you get another 248,000!


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