Introduction
Whilst CRD Performance will accept bookings from customers who just want their Diesel Particulate Filter problems resolved or Filters removed and their vehicles computer software re-programmed, we strongly recommend they read all the following sections. These informative sections below will help you decide whether to book your vehicle in for a full diagnostic check and correct repair, or just a low cost short term remedy if you want to keep costs to a minimum.
If you’d prefer to book your vehicle in for DPF removal or related repairs but without reading all the sections then at least read the DPF Failure-Repair Procedure section before contacting us, this will save us all valuable time in trying to explain what’s involved.
Repair Procedure
1. Book your vehicle in with us either by phone or at reception and explain to us any concerns you have which you think may be related to a DPF problem or diesel running fault.
2. If we think we may be able to help we’ll advise you leave your vehicle with us for the day at the next mutually agreeable time and date. Your only commitment with us at this point will be to just 1 hour’s diagnostic labour charge currently set @ £65.00 + vat (£78.00).
3. CRD Performance will carry out an initial appraisal of the DPF and engine management system using various pieces of test equipment, including a Scan Tool, boost gauge and sometimes Rolling Road to help identify any areas of concern. This appraisal will not repair your vehicle but it will give us an insight into any faults present or pending and help us advise you of what further tests or repairs are needed next. We will also inspect the external condition of the DPF and remaining exhaust system should we suspect that DPF removal might be necessary.
4. Any fault codes read using a scan tool will be recorded and then erased prior to the vehicle being taken on a road test. If any fault codes return that we suspect may be responsible for preventing the management system from regenerating the DPF then we’ll discuss these with you.
5. Following our appraisal we will contact you to discuss our findings and depending on if you intend keeping the vehicle or disposing of it shortly we’ll advise the best way forward.
Repair Options
We advise customers not to decide straight away to have the DPF removed and their vehicles ECU reprogrammed to ignore the missing DPF. If they really insist then we’ll do as they ask but only if they are prepared to accept any consequences. On some vehicles this may be OK whilst on some others this may bring on the engine management light or deliver restricted power. Even we can’t be sure since two identical makes and models of similar ages may have different manufacturer’s software versions in their ECU’s.
The correct repair method is always to identify why the DPF has become blocked and then consider if the best option to suit the customer is to remove the DPF and reprogramme the ECU or rectify the initial cause. It is also recommended that if the DPF is to be removed an attempt is made to regenerate first and to empty the ECU’s fill counters to minimise the risk of any running problems following removal.
As worst case scenarios consider this, a Vauxhall Vectra 3.0 V6 CDTI was booked into our workshop with a suspected blocked DPF.
The vehicle was correctly diagnosed as having a blocked DPF; this was confirmed using a Scan Tool to read the stored fault codes and to monitor excessive pre-DPF back pressure. The fault code was erased but didn’t return during its road test even though the engine was obviously lacking in power and drove awful.
In this situation removing the DPF and reprogramming the ECU would have prevented the engine management light from coming back on for DPF faults and would have restored some of the engines lost power.
On further investigation the fault was confirmed to be a blocked DPF but luckily for the customer we diagnosed and rectified the underlying cause. Whilst attempting a forced regeneration using a Scan Tool and our own 3D Re-map box we observed that any additional fuel injected into the DPF wasn’t being burned due to a shortage of air. The remedy involved removing the intake manifold and thoroughly cleaning the swirl flaps and leaking EGR valve and also topping up the engine oil level before the ECU would allow a forced regeneration. Following a 15 minute run on our rolling road the engines normal power was restored and without the need to remove the DPF.
The point here being that having your DPF removed and ECU reprogrammed in a similar situation could leave you several hundreds of pounds out of pocket with some “E-Bay re-mapper” who doesn’t really understand DPF systems. The DPF that’s now been removed could have been regenerated but instead you’re left with an engine in limp mode that lacks power, the EML light’s on but now without the DPF present now smokes heavily under acceleration.
About DPFs
Diesel particulate filters have been voluntarily used by only a few vehicle manufacturers for several years now but only since about 2009 it has been compulsory for all vehicles to be fitted with them to help achieve strict new Euro 5 emissions. These filters can often be confused with the catalytic convertor or silencer box as they look similar and are usually incorporated as part of the exhaust front pipe near to the engine.
Their purpose is to trap diesel particulate matter or soot as it’s normally called, all diesel engines smoke under hard acceleration, especially when cold, due to the entire diesel not being burnt. Even with the major advances in high pressure common rail diesel systems not all of the diesel combusts and this can be seen as black smoke coming from the vehicles tailpipe where a DPF hasn’t been fitted. If you follow a diesel vehicle that’s accelerating and you don’t see any smoke it’s more than likely fitted with a DPF or had its fuel turned down.
Sooner or later, depending mainly on driving style or conditions, these filters will become restricted or blocked but vehicle manufacturers have taken steps to help prevent this from happening. Periodically these filters need to be cleaned or emptied but without removing them from the vehicle, this process is often referred to as DPF Regeneration.
The engine management system monitors the DPF’S soot fill percentage, often referred to as the fill counter and decides when regeneration is necessary. As well as monitoring the DPF’S back pressure to indicate a partially blocked filter some ECU’s are programmed to carry out regeneration based on mileage covered or hours driven.
DPF Regeneration
Regeneration is the term used to describe cleaning the DPF, during this process the “wet and sooty” particulate matter is subjected to further combustion inside the DPF itself. Surface temperatures inside DPF can exceed 600 Degrees Celsius at which point the soot turns into a hot white ash which is then harmlessly emitted from the tailpipe.
There are 3 ways these DPF’s can be regenerated, these are passively, actively or forced.
Passive regeneration.
This type of regeneration takes place automatically but only if the vehicle is used often and for medium to long journeys, what also helps is if the vehicle is driven hard where the DPF benefits from plenty of hot exhaust gas flow. Brisk driving helps generate higher exhaust gas temperatures with the added benefit of forcing the ash waste out of the exhaust system.
Active regeneration.
If the engine management system detects that the vehicle isn’t being used in a manner to allow passive regeneration and detects a higher than normal DPF exhaust back pressure reading it should initiate active regeneration. This function occurs automatically but only when certain conditions are met. During active regeneration diesel is injected into the engine on the exhaust stroke which allows it to pass unburned through the open exhaust valves and into the DPF where it combusts with the excess abundance of unused oxygen. During this forced regeneration temperatures in the core of the DPF will exceed 600 Degrees Celsius, active regeneration normally occurs whilst the vehicle is being driven at steady motorway cruising speeds and may last around 30 minutes before the cycle is complete. The problem is however, how the engine management system knows how long the vehicle is going to be driven at steady motorway cruising speeds, the answer is that it doesn’t, this in itself can lead to problems.
It is not unusual to sometimes see a diesel vehicle being driven at speed during regeneration with excessive smoke being emitted from the tailpipe or for the owner to observe a dramatic increase in the instantaneous MPG during this process. Sometimes when a vehicle is stopped and re-started whilst interrupting the DPF regeneration excess smoke can be seen from the tailpipe. Some, but not all vehicles will alert the driver with a dash warning light if the DPF regeneration cycle is taking place or, more importantly, has not been completed for whatever reason, should this occur the driver must refer to the owner’s manual.
Forced Regeneration.
If both passive and active regeneration attempts have failed to empty the DPF fill counter and with the exhaust back pressure high, the only option left is to carry out a forced DPF regeneration. This process involves using a diagnostic Scan Tool connected to the vehicles 16 pin OBD (on board diagnostic) socket which instructs the vehicles management system to regenerate the DPF, this sometimes takes place with the vehicle stationary in the workshop. In most instances this procedure can only selected and implemented if there are no stored error codes in the ECU, if error codes are present it’s more than likely that these have prevented active regeneration taking place and may be the root cause of the DPF problem.
Provided everything is in order the regeneration can begin and in a similar way that active regeneration is performed unburned diesel is injected through the engine and into the DPF, during regeneration the engine speed can sometimes be raised above 3000rpm. As before, the diesel combusts with the oxygen and raises the inner DPF core temperature to in excess of 600 degrees Celsius which turns any soot residues into hot white ash. This procedure can last anything up to an hour and must be carried out in a well ventilated area also ensuring there isn’t anything under the vehicle that might catch fire from the extreme heat generated from the DPF.
This forced regeneration is far more effective than both the passive or active method as the vehicle is most often stationary and the DPF reaches much higher temperatures due to less air cooling beneath the vehicle.
Failed Regeneration.
Sometimes regeneration fails to recover a blocked DPF either because the material inside the unit has melted or disintegrated or it’s just too badly blocked.
Successful regeneration.
If regeneration has worked there are now two options to consider, either to leave the DPF in place or have it removed, the correct decision must take into account the vehicles intended use and driving style. If the vehicle is to be used for short, stop start journeys, with few frequent long distance runs then you’re better off with the DPF removed. If you intend driving the vehicle hard and making frequent long journeys then you may be as well leaving the DPF in place and saving the correct removal cost. It may be that you’ve recently purchased the vehicle and the previous owners driving style was responsible for blocking the filter whereas yours might not.
DPF Removal
Removing these filters can be a labour intense job as some particulate filters are part of the exhaust manifold or front pipe assembly, these are often fitted as close to the engine as possible to help maintain a high temperature and to assist fast warm up. V6 and V8 engine vehicles are often even more difficult to work on due to steering racks, sub frames and turbochargers etc. getting in the way and restricting access to exhaust manifold nuts or bolts. Older vehicles present even more problems due to corrosion or seizure, making it necessary for the garage to use in extreme cases oxy-acetylene burning equipment.
After removing the DPF it will be necessary to either fabricate or purchase a replacement by-pass pipe ensuring that any exhaust pressure and temperature sensor take off points are retained. With the DPF now removed the engine management system may still look to see that these sensors are present and if not connected the ECU might detect an error, switch the engine management light on and enter limp mode making the vehicle almost undriveable.
Software Upgrade
If the Diesel Particulate Filter is physically removed from the exhaust system and the ECU not re-mapped to accept the changes then sooner or later the engine management system could go into limp mode, (LOS) limited operating strategy. When in limp mode the vehicle may have restricted power and if it’s an auto it might even default into a high gear to restrict acceleration.
Whilst monitoring pre, and on some vehicles post DPF differential pressures the vehicles’ management system monitors the current state of the DPF’s and detects if one or more are present.
Software DPF removal involves reprogramming the vehicle’s ECU to ignore any abnormally high or low readings from either the pre or post DPF differential pressure sensors. As previously mentioned, it is still necessary for all DPF pressure sensors to be present and working, software changes can only be made to open up pressure parameters, preventing regeneration, not to ignore the sensors altogether.
Failure Causes
UNDER CONSTRUCTION
Failure Prevention
UNDER CONSTRUCTION
Questions & Answers
UNDER CONSTRUCTION