DPF / EGR Solutions

What is a DPF?

A diesel particulate filter (DPF) removes diesel particulate matter, or soot, from the exhaust gas of a modern diesel engine.

Once a certain amount of soot has built up, the car starts a regeneration. It injects diesel (or, on some cars, another fluid) to raise the exhaust temperature high enough to burn the soot off, leaving a small ash deposit and a clean filter. This cycle repeats for the life of the DPF, which you can usually find in your handbook.

What causes DPF problems?

A DPF that is working properly causes only a slight increase in back pressure, which takes a little away from the engine's performance and fuel economy. The real problems start when the filter cannot regenerate as it should. Many things play a part, but these are the three we see most often:

• System faults. Because regeneration is a combustion process happening inside the exhaust, the ECU controls and monitors it closely. Any engine fault will stop the car from regenerating.
• How the car is driven. Regeneration only happens when certain conditions are met, such as a minimum road speed, engine temperature and length of drive. Cars driven daily on longer commutes give far fewer problems; cars used mainly for short journeys give the most. It is worth bearing in mind when deciding which solution is right for you.
• DPF ageing. On most vehicles the DPF is a service item. The service schedule may say how often it should be checked and when it is expected to need replacing. Cleaning or forcing a regeneration on a filter that is overdue for replacement may not work.

What are my solutions to a DPF problem?

We work through the options in order, starting with finding out exactly why the filter is not regenerating. Fixing a blocked DPF without fixing the reason it blocked only means it will block again.

1. Advanced diagnostics
2. Forced regeneration
3. Chemical cleaning

1. Advanced diagnostics

We believe diagnostics are the key to a successful DPF repair. That means the data from the vehicle, but talking to you is just as important. During advanced diagnostics we look at:

• Engine fault codes (DTCs). These tell us why the DPF is giving problems. They may pinpoint the fault straight away, or show where further diagnostics are needed.
• Live engine data. We read the live data being fed back to the engine ECU on our diagnostic equipment. Everything has to read correctly for the DPF to work fully.
• Your everyday driving. We ask what a normal week of driving looks like for the car. This often matters most of all: if a car is not regularly driven over longer distances, it simply will not regenerate properly.

2. Forced regeneration

If the DPF has not regenerated by itself and the soot level is high, a forced regeneration is the first step. We use diagnostic equipment to make the car run a regeneration cycle, either while driving or stationary.

We recommend this after advanced diagnostics, so we know the DPF will keep regenerating on its own once it has been cleared. That will only be the case if:

• No engine faults are present and all sensor live data is reading within the expected range.
• Longer journeys make up most of the vehicle's regular driving.

Examples of where a forced regeneration works:

• A faulty sensor stopped the DPF regenerating, and the sensor has now been replaced.
• The DPF was not regenerating because the car was not being driven far enough, but a change in circumstances means it will now be driven on regular longer journeys.
• A component failure caused the DPF problem and has now been fixed, for example an exhaust gasket leak, an injector or a turbocharger.

3. Chemical cleaning

If the soot level is high and a forced regeneration cannot be completed, chemical cleaning is the next step. We remove the sensors from the DPF and spray cleaning fluid into the filter using specialist equipment.

Because it works on the same basis as a forced regeneration, the same rules apply. We recommend it after advanced diagnostics, and it will only keep the DPF working if:

• No engine faults are present and all sensor live data is reading within the expected range.
• Longer journeys make up most of the vehicle's regular driving.

Examples of where chemical cleaning works:

• A faulty sensor stopped the DPF regenerating, and the sensor has now been replaced.
• The DPF was not regenerating because the car was not being driven far enough, but a change in circumstances means it will now be driven on regular longer journeys.
• A component failure caused the DPF problem and has now been fixed, for example an exhaust gasket leak, an injector or a turbocharger.

When neither will work

If a fault is still present, if the car will carry on doing mostly short journeys, or if the filter is overdue for replacement, a forced regeneration or clean is unlikely to last. In that case we will explain why and talk you through the options before any work is done.

What is an EGR valve?

Exhaust gas recirculation (EGR) feeds part of the engine's exhaust gas back into the engine. The EGR valve controls how much gas goes through this process.

EGR systems exist only to reduce emissions, often at the expense of engine life and reliability. Unlike a DPF, the EGR process has downsides even when it is working correctly:

• Engine wear. Carbon-rich exhaust gas fed back into the cylinders lets carbon particles wash past the piston rings into the oil. That makes the oil more abrasive and more acidic, which shortens engine life.
• Less power. Exhaust gas has a higher specific heat than air, so it lowers the combustion temperature in the cylinders and reduces the power made on each combustion cycle.
• Harder work for the DPF. The lower combustion temperature slightly reduces nitrogen oxide (NOx) emissions, but NOx is the main thing that burns off soot caught in the DPF. As a result, diesel (or another fluid) has to be used to clean the DPF actively.
• Sticky deposits. The intake system is otherwise dry, but EGR brings soot, unburnt fuel and oil into it. This mixes with cold air and oil vapour and can build up as a sticky tar in the intake manifold and valves. It can also cause problems with the EGR valve itself, manifold flaps, anti-shudder valves and similar parts.

What causes EGR problems?

The way the EGR works means it fouls with soot from the exhaust. Most of the problems we see come from that sticky tar jamming the mechanical parts of the valve or damaging the electronics of modern electronic EGR valves. It is worse on cars that do short, stop-start journeys, or that do not use the whole rev range on each drive.

What are my solutions to an EGR problem?

As with a DPF, we start with advanced diagnostics to confirm the exact fault in the EGR system, using fault codes, live data and a conversation about how the car is driven.

Depending on what we find, an EGR valve can be cleaned or replaced. Be aware that no amount of diagnostics beforehand can promise how long either will last: if the car keeps doing the kind of driving that clogged the valve, the deposits will build up again. We will explain what we have found and what to expect before any work is done.

Disclaimer

Removing or disabling emissions equipment, such as a DPF, EGR valve or AdBlue (SCR) system, on a vehicle used on public roads is illegal in the UK and in most other countries, and the vehicle will fail its MOT. The same applies to raising exhaust noise above the legal limit.

We only carry out removal work, or supply parts for it, on vehicles used off-road, in competition or for export. The customer is responsible for making sure the vehicle complies with the law wherever it is used, and we cannot accept responsibility for a vehicle driven on public roads with emissions equipment removed. We cannot road test a vehicle after this work.

For road cars in Northern Ireland and beyond, our focus is on diagnosis, cleaning and repair. If you have any questions, ask us before work begins.