DPF warning light switches on – what now? How to clean a diesel particulate filter

DPF warning light switches on – what now? How to clean a diesel particulate filter

Diesel cars were considered particularly environment-friendly for quite a long time. Low fuel consumption and the possibility of using bio-fuel gave diesel drivers a clear conscience. The self-igniter, however, turned out to be a dangerous emitter of health-damaging substances.

soot form DPFThe soot, an unavoidable by-product of diesel combustion, is the main problem. Soot is a residue of burnt fuel.

In older diesel cars without any exhaust filtering, the caked substance is blown into the environment. When inhaled, it is equally dangerous as cancerogenic substances such as nicotine and tar from cigarettes. Therefore, it became legally mandatory for car manufacturers to equip new diesel vehicles with an effective exhaust filtering system.

Effect is only temporary

catalytic converter constructionContrary to the catalytic converter of petrol cars, the diesel particulate filter is only partly a substance converter. The DPF is what its name says: it filters the soot particles from the exhaust. But no matter how large the filter is, at a certain point it can no longer maintain its filtering performance. The DPF is self-cleaning.

The soot is incinerated to ash by an artificially boosted exhaust temperature, resulting in a reduction of the volume remaining in the filter. However, a certain amount of ashes remains in the filter as a residue and eventually the diesel filter is filled up to capacity.

DPF warning lightThe self-cleaning program is at the end of its possibilities and the engine control signals an error, which is indicated by a control light in the dashboard.

This warning should not be ignored. When the DPF is completely clogged, there is a risk of serious engine damage. Before that happens, engine performance is obviously reduced and fuel consumption rises.

Repair is legally required

DPF at MOT inspectionA perfectly functioning DPF is essential for passing MOT inspection. If the inspection service finds a clogged filter, an MOT certificate will be refused. MOT or any regulatory board generally advises filter replacement. Depending on car model, this can turn out to be quite expensive. A new filter and its replacement costs 1100 EUR (± £972) at least, and possibly even more. However, there is an alternative.

Cleaning instead of buying a new filter

There are proven and certified methods of DPF cleaning, to make it as good as new. The possibilities are:

– cleaning by burning
– cleaning by rinsing

or a combination of both procedures.

burning DPF cleanIn order to burn it clean, the de-installed DPF is put in a burning oven, where it is heated until all remaining soot is burned to ashes. Subsequently, the filter is blown clean with pressurised air until all ashes are completely removed.
Rinsing DPF cleanRinsing is in fact blowing the filter clean with a watery cleaning solution. With this procedure, the filter is pressurised from both sides as well, which is necessary for adequately cleaning the DPF from ashes. Ashes accumulate in closed channels. If the filter is cleaned in only one direction, the ashes stay put, rendering the filter cleaning ineffective.

Branded products are inadequate

diy cleaning of DPFThis is the main problem of DIY solutions for filter cleaning. There are plenty of miracle solutions on the market, promising the perfect cleaning of the particulate filter. Unfortunately, also renowned companies which are actually principally known for their excellent lubricants, have joined this race.

They all advertise solutions for injecting in the thread hole of the lambda sensor in order to clean the filter. As stated previously: a full cleaning of a filter requires treatment from both sides. When installed, only one-sided cleaning is possible. Therefore, these DIY solutions are not really suitable for filter cleaning.

The problem is more serious

DPF cleaning detergentsThe available methods are only partly effective. The injection method has another problem: the cleaning detergent mixing with soot and ashes could form a rock-hard plug. In that case even the toughest cleaning methods such as burning it free at more than 1000 °C has no effect.

Filter damage is so serious that replacement by a new element is the only option – and this is unfortunate. A professional cleaning with certified effectivity is available starting at £180, which is 1/5 of the price of the cheapest new DPF.

DIY disassembly saves money

DIY disassembly of particulate filterThe disassembly of the DPF is not very difficult and you can save money by doing it yourself and sending it to a service provider. In the worst case a lambda or pressure sensor can break off. The service provider offers drilling and repairing the thread hole as additional service. This is always cheaper than buying a new particle filter.

thoroughly inspect the entire exhaust pipingWhen removing the DPF you should thoroughly inspect the entire exhaust piping. The filter unit is by far the most expensive exhaust system component. With the car jacked up anyway, it is the proper occasion for replacing all rusty or defective exhaust components.

Re-using a lambda sensor is a question of philosophy. A repaired DPF does not require a new lambda or pressure sensor. In any case, replacing the part on this occasion does no harm and it will establish a new starting point for the entire unit.

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Always look for the cause

Normally, a DPF lasts 150.000 km on condition of varying driving circumstances. Longer distances on the motorway of more than an hour should regularly occur. When driving a diesel only on short distances only, the required engine and exhaust temperatures for DPF self-cleaning are never reached.
the cause of defective DPFIf the DPF clogs sooner, the cause could be a serious engine defect. In this case, engine oil is penetrating into the combustion chamber and the particulate filter. Causes for this can be:

– defective turbocharger
– defective cylinder head gasket
– defective valve stem seal
– defective piston rings

There are procedures for investigating these defects. Before installing the new or repaired DPF, the engine should be checked for this kind of damage. Otherwise the new component will clog soon and the engine damage could possibly get worse. Filter replacement would be in vain.

Foto: studioloco, Alraun, A.A. Mariscal Troncoso, Sista Vongjintanaruks, Ody_Stocker / shutterstock.com

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