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UNDERSTANDING THE DPF SYSTEM

Emissions requirements for new vehicles require Particulate Filters to be fitted to the exhaust of diesel vehicles since the ‘Euro 5’ standards were enforced in 2009. Prior to this many vehicles also have a DPF fitted in anticipation of the change to regulations. This ‘Euro 5’ and beyond standards aim to deliver reductions of >80% in soot (diesel particulates). However, these filtration systems are not without problems causing DPF warning lights, engine limp mode safety activation, reduced efficiency/mpg and poor engine performance.


The diesel particulate filter is mounted as part of the exhaust system. In order for the filter to operate correctly, it must regularly run a regeneration process to burn off the continuously accumulating soot. This process is completed by precisely regulating an increased temperature of the exhaust gas passing through the filter which then burns away the carbon deposits. To do so a sensor transmits data to an engine control unit that then calculates the precise requirement for post-injection fuel to increase the temperature during the regeneration phase. As with any filter, the DPF must be regularly emptied otherwise, over a period of time, it will start to clog up and will eventually become partially blocked. Passive regeneration of the DPF can only occur at fast speeds on a motorway or A-road so with all the local driving and short journeys for many vehicles this process cannot occur often enough eventually leading to clogging of the DPF.

HOW DOES THE DPF REGENERATION PROCESS WORK?

Passive regeneration:

The DPF system is designed in such a way that when the engine is consistently running at approximately 2,500 rpms or more (e.g. on a motorway or fast A-road) the exhaust gas temperatures exceed 350°C soot particles are constantly being burned off without any engine management intervention.

Active Regeneration:

Where the vehicle is predominantly used for urban mileage the exhaust gas temperatures fail to get hot enough passive regeneration is no longer achieved. Therefore soot particles are no longer being burned off so start to accumulate inside the filter. This leads to clogging of the filter and when a threshold is reached the engine’s control unit (ECU) triggers the active regeneration at its next opportunity. The amount of soot accumulated inside the DPF is calculated by the ECU based on:- ‘Driver profile’ – whereby the ECU records the pattern of exhaust gas and oxygen temperature sensor readings and then calculate the degree of saturation, and DPF flow resistance’ – whereby the ECU records signals from sensor regarding flow, temperature and pressure and then calculates of the degree of saturation.

The pressure is measured at both the inlet and outlet of the DPF and the degree of saturation inside the filter is measured by the pressure sensor calculating the difference between the two readings. As the filter becomes clogged the voltage transmitted by the pressure sensor to the ECU rises. At a manufacture set voltage reading the ECU will proceed to raise the temperature of exhaust gas to approximately 600°C thus actively starting the regeneration process. The ECU instructs this increase in temperature by:

  • Regulating air flow through the Electronic Throttle Control (ETC).
  • Switching the Exhaust Gas Regeneration (EGR) valve so that it recycling exhaust gases thus increasing engine combustion temperature.
  • Enforcing a post-injection following the principal injection in order to increase the combustion temperature.
  • Enforcing a second post-injection which leads to unburnt fuel evaporating inside the combustion chamber. The unburnt hydrocarbons are oxidised by vapour inside the catalyst converter. During this stage temperatures inside the DPF can reach 620°C.
  • The sensor signal, upstream of the DPF, supplies the ECU data to determine the quantity of fuel to be injected during the second post-injection.
  • Forced regeneration:

    When the DPF system has exceeded a set level of saturation it becomes impossible for the vehicle to perform a passive or active regeneration. A mechanic may at this stage attempt what is known as a forced regeneration using a computer to instruct the DPF system to heat up (similar to the active regeneration process) and burn off the excess soot. Depending on the vehicle this will either be done whilst driving or possibly stationary with the engine running and the ecu controlling the RPMS.


    Unfortunately all too often forced regenerations will fail or only be beneficial for a short period of time. Why? Simply because either the saturation is too high or the operator has not diagnosed and repaired the fault causing the DPF system to fail the process.


    If a forced regeneration fails its common practice you’ll be told by a mechanic that a new DPF is required and at huge expense. In most instances this advice, even when it’s from the manufacturer dealers, is inaccurate!


    What it more than likely means is the mechanic has reached the limit of their understanding of a very complicated system and therefore assumes the DPF has completely failed. Or in the instance of it being a manufacturer dealer giving such advice, they are simply a business looking to make a profit. In our experience, this diagnosis is rarely correct. For most replacing the DPF will only resolve the problem short-term, with the fault still present it’s only a matter of time before the new expensive DPF also becomes saturated.

    If your vehicle has a DPF issue, or has even failed a DPF regeneration by a professional, and therefore requires professional intervention to diagnose and resolve the problem there is no better alternative than a skilled UKCC technician.

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    Modern Reviews Tabs | UKCC Auto Techs
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    Over 50,000 Satisfied UK Customers Since 2016

    What Our Customers Say

    Latest from all platforms
    10
    Posted 6 October 2026

    High Standard of work

    Just to say Matts work was to a high standard. He arrived early, focused on the task and did a great job. He completed all tasks required and ran a thorough check afterwards. Very reassuring! A genuine technician and people person. I have no concerns recommending Matt and his company.

    Verified reviewer
    Job location: KT22 Checkatrade
    ★★★★★

    Booked Winston in today for a swirl flap bypass , one of the most genuine mechanics I've met . After his diagnosis, explained about the split intercooler pipe ( somthing my local garage could not discover ) and best to fix that first before proceeding with swirl flaps . Best £90 ive ever spent . I may need him again after fix of intercooler pipe for the bypass , but a big thank you for your honesty .

    RH
    Ryan Hague Sep 25, 2026
    Trustpilot

    Excellent service

    I was really impressed with the information Jason provided me with. Nice to come across an honest company who put customers first! Highly recommend.

    10
    Posted 8 November 2025

    Job well done

    Thank you Matt, Arrived bang on time carried out arranged work to my Audi and a bit more and some great advice .

    Verified reviewer
    Job location: RH10 Checkatrade
    ★★★★★

    Very professional job done by Matt. First day the car didn’t delete for some software issue but he promptly came over to re-do the job to make sure everything worked properly next day.

    AM
    Alan Moore Sep 22, 2026
    Trustpilot

    I had Technician Cristian Nicolaie come…

    I had Technician Cristian Nicolaie come to my home on Friday morning to diagnose and clean my DPF filter and remove carbon build-up from the engine. From the moment Cristian arrived, he was polite, friendly and professional. He asked me a few questions about the car, explained what he was going to do and talked me through the possible cause of the problem. He also gave me some really useful advice on how to help prevent the problem from happening again. Cristian carried out the work professionally and got the car back to normal. The diagnostic test afterwards showed that everything was working as it should. What made this even more important to me was that I was due to go away that day and had to tow my caravan. After speaking with Cristian, he gave me complete confidence that the car was going to be okay — and he certainly didn’t disappoint. I towed my caravan with no problems at all, and the car performed perfectly. I live in the BS15 area, and I would have absolutely no hesitation in recommending Cristian Nicolaie to anyone experiencing problems with their car. If the other technicians within the company have the same level of professionalism, knowledge and customer service as Cristian, then I would happily recommend the company as well.

    ★★★★★
    10/10
    Read all reviews →
    10
    Posted 6 October 2026

    High Standard of work

    Just to say Matts work was to a high standard. He arrived early, focused on the task and did a great job. He completed all tasks required and ran a thorough check afterwards. Very reassuring! A genuine technician and people person. I have no concerns recommending Matt and his company.

    Verified reviewer
    Job location: KT22 Checkatrade
    10
    Posted 8 November 2025

    Job well done

    Thank you Matt, Arrived bang on time carried out arranged work to my Audi and a bit more and some great advice .

    Verified reviewer
    Job location: RH10 Checkatrade
    10
    Posted 14 August 2025

    Full Carbon Clean and remap

    I had the pleasure of meeting Matt today. He was on time, gave great advice, honest feedback, great sense of humour - everything you would want from your technician. Never makes you feel stupid. Explained how the remap works. I'm only disappointed he didn't take a picture of my car for his portfolio.

    Verified reviewer
    Job location: SL9 Checkatrade
    10
    Posted 9 June 2025

    Cleaned DPF and engine very sufficient. Very happy with the service highly recommended.

    Cleaned DPF and engine very sufficient. Very happy with the service highly recommended.

    Verified reviewer
    Job location: RH12 Checkatrade
    10
    Posted 9 June 2025

    Egr issue resolved on my Audi in Kent

    Very good and efficient

    Verified reviewer
    Job location: ME1 Checkatrade
    10
    Posted 20 May 2025

    DPF and egr clean and reset

    Great advice from Cristian the technician who advised and then did the job very well thank you very much.

    Verified reviewer
    Job location: NP44 Checkatrade
    ★ ★ ★ ★ ★
    4.5/5
    Read all reviews →
    RH
    Ryan Hague Sep 25, 2026
    Trustpilot

    Excellent service

    I was really impressed with the information Jason provided me with. Nice to come across an honest company who put customers first! Highly recommend.

    AM
    Alan Moore Sep 22, 2026
    Trustpilot

    I had Technician Cristian Nicolaie come…

    I had Technician Cristian Nicolaie come to my home on Friday morning to diagnose and clean my DPF filter and remove carbon build-up from the engine. From the moment Cristian arrived, he was polite, friendly and professional. He asked me a few questions about the car, explained what he was going to do and talked me through the possible cause of the problem. He also gave me some really useful advice on how to help prevent the problem from happening again. Cristian carried out the work professionally and got the car back to normal. The diagnostic test afterwards showed that everything was working as it should. What made this even more important to me was that I was due to go away that day and had to tow my caravan. After speaking with Cristian, he gave me complete confidence that the car was going to be okay — and he certainly didn’t disappoint. I towed my caravan with no problems at all, and the car performed perfectly. I live in the BS15 area, and I would have absolutely no hesitation in recommending Cristian Nicolaie to anyone experiencing problems with their car. If the other technicians within the company have the same level of professionalism, knowledge and customer service as Cristian, then I would happily recommend the company as well.

    MS
    MR SHANE SMITH Sep 6, 2026
    Trustpilot

    Ukcc auto techs Christian attended my…

    Ukcc auto techs Christian attended my property to diagnose my van which had dpf issues and a ad blue problem. Christian was very informative explaining what was happening with my van. Christian then proceeded to clean the dpf and the ad blue fault was very professional explaining the process at all times. I would recommend Christian to anyone who has problems with there dpf or any ad blue faults thanks again Shane

    AG
    Ariane Grimshaw Aug 21, 2026
    Trustpilot

    Extremely happy with the service…

    Extremely happy with the service Cristian provided - he was knowledgeable, professional and efficient. Would highly recommend!

    KI
    Kirsty Aug 20, 2026
    Trustpilot

    I had a stage 3 clean done today

    I had a stage 3 clean done today. The gentleman was very polite and knowledgeable. Very good service. Would recommend to others.

    RR
    robert righton Aug 20, 2026
    Trustpilot

    Christian DPF repair

    Christian arrived as planned and was very helpful in explaining the diagnostics and what was needed Repair work carried out promptly I had a further issue later in day and Christian met me in evening to sort that issue also at no extra cost Highly recommend him and will be using him again if needed Rob

    ★★★★★
    4.4/5
    Read all reviews →
    ★★★★★

    Booked Winston in today for a swirl flap bypass , one of the most genuine mechanics I've met . After his diagnosis, explained about the split intercooler pipe ( somthing my local garage could not discover ) and best to fix that first before proceeding with swirl flaps . Best £90 ive ever spent . I may need him again after fix of intercooler pipe for the bypass , but a big thank you for your honesty .

    ★★★★★

    Very professional job done by Matt. First day the car didn’t delete for some software issue but he promptly came over to re-do the job to make sure everything worked properly next day.

    ★★★★★

    Thank you for the 5-star rating, Thomas! We’re delighted you had a great experience and appreciate your support. We look forward to welcoming you back soon.

    ★★★★★

    best work ...

    ★★★★★

    Thank you Christian being so prompt in coming to fix and diagnose the problem I have with my vehicle , service was very prompt with excellent knowledge behind him . I would definitely recommend Christian 100% . Will definitely recommend and use him again . Thankyou for your help

    ★★★★★

    Perfect job thank you so much

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