Diesel Particulate Filters
Diesel Particulate (DPF)
Detailed below is important information outlining the
function and features of the Diesel Particulate filter which all members of your
team need to be aware of.
Diesel particulate filters are becoming more commonplace on
diesel engines, particularly sizes 2.0L upwards. This is in order to reduce the
exhaust emissions as required by European legislation.
The prime reason for a DPF is to reduce particulate matter
entering the atmosphere. Particulate matter is found in the form of soot, which
is produced during diesel combustion. The DPF traps most of the soot which would
normally travel down the exhaust and into the atmosphere. The DPF can hold a
certain amount of soot, but not a huge quantity and therefore it needs to go
through a process called ‘regeneration’ in order to clear the soot loading. When
the soot goes through a ‘regeneration’ process it will be converted to a much
smaller amount of ash. The ash is non-removable. There are two types of
‘regeneration’, passive and active.
During long motorway journeys, passive regeneration will
occur. This needs no intervention from the engine control unit. Due to the
raised exhaust temperatures on a long journey (temperatures between 350 and
500°C), the procedure occurs slowly and continuously across the catalytic-coated
(with platinum) DPF. The catalytic-coated DPF is situated close to the Engine,
therefore the exhaust gas temperature is high enough (500°C) to ignite the soot
particles. Due to this soot is burned-off and is converted into a smaller amount
of ash.
Active ‘regeneration’ is when the ECU intervenes when the
soot loading in the DPF is calculated to be 45%. The procedure lasts for about 5
– 10 minutes. Specific measures are taken by the ECU to raise the engine exhaust
temperature to above 600°C, these include switching off the exhaust gas
recirculation and increasing the fuel injection period to include a small
injection after the main injection. The soot particles are oxidised at this
temperature.
Typically...
The ECU will trigger a regeneration process, if for some
reason this is aborted, ie. customer slows down, stops etc, the process will be
resumed when regeneration conditions are once again met, above 60km/h (38mph).
This will continue for 15 minutes.
If after 2 attempts of 15 minutes, a successful
regeneration has not been possible, the loading will increase. At 50% soot
loading, the ECU will continue to maintain maximum exhaust temperatures of 600°C
to 650°C to cause a regeneration process. The system will try to run a
regeneration process for 15 minutes. If unsuccessful, the system will repeat
this process for a further 15 minutes, if still unsuccessful, the DPF light on
the driver display panel will then be lit.
The owners handbook states, the DPF symbol lights up to
indicate that the diesel particulate filter has become obstructed with soot due
to frequent short trips. When the warning lamp comes on, the driver should drive
at a constant speed of at least 60 km/h for about 10 minutes. As a result of the
increase in temperature the soot in the filter will be burned off. If the DPF
symbol does not go out, the driver should contact an authorised Volkswagen
repairer and have the fault rectified.
At 55% soot loading the DPF light is lit on driver display
panel. At this point the customer should follow the advice in the handbook. If
they ignore this information and continue driving the vehicle until the soot
loading reaches 75% without successful regeneration, additional warning lamps
will light up. At this point the customer will also be complaining of lack of
power, etc.
At 75%, regeneration is still possible with the use of a
diagnostic scan tool. Only when the loading is above 95%, is it necessary to
replace the DPF unit.
Operating StatusSystem Response
45% DPF Load Level 1
Normal Regeneration
50% DPF Load Level 2
Regeneration at maximum exhaust temperatures
55% DPF Load DPF lamp
Regeneration from 60 km/h onwards
("See operating manual")
75% DPF Load DPF, SYS and MI lamp
Torque limitation, EGR deactivation,
Regeneration via scan tool only
95% DPF Load Replace the DPF Unit
Most warranty companies confirmed that if there is no fault
on the vehicle and DPF regeneration has been unsuccessful due to the customers
driving style and the customers failure to comply with the instructions in the
handbook, DPF replacement will not be paid for by warranty.
Common causes for complaint
• Frequent short journeys – Regeneration conditions are not
met.
Not recommended for sale in the Channel Islands and inner
city driving.
• Customers who continue to drive the vehicle with DPF
light on – Continued
driving with the DPF light on and without successful
regeneration results in
excessive soot loading of the DPF, to a point where it is
above 95% loaded.
At this point regeneration is not an option and replacement
of the DPF is
necessary.
• Faultcode: particle filter bank 1 malfunction – Common
fault code. This does
not only relate to the DPF itself, but the entire exhaust
gas handling system. This
can be caused by defective temperature sensors, pressure
sensors, additive
system components (if applicable), poor connections, wiring
issues, etc.
Important Information
• Before diagnosing a problem vehicle or attempting to
perform an emergency
regeneration, it is important to obtain a full diagnostic
log and read out relevant
measured value blocks. These MVB’s contain important
information on the
condition of the DPF system and are essential in diagnosing
the fault. When the
DPF light is illuminated, it does not necessarily mean that
the DPF requires
regeneration.
• If a problem vehicle arrives with the DPF light, the
engine management light and
the emissions light on. If during your diagnosis and
reading of relevant MVB’s,
you find that the soot loading exceeds 75% (but is still
below 95%), an
emergency regeneration procedure must be performed with a
scan tool.
Further to this, the customer needs to be educated. They
need to understand
why the lights have appeared on the dash panel. Their
attention needs to be
brought to the owners handbook instructions, so that they
are aware of what the
DPF light means and what to do when it appears. This should
prevent
unnecessary repeat visits for regeneration purposes.
We have also found that as the car gets older 30K+ miles, you will notice that the regeneration takes place more often.
ALWAYS, check your oil before any long journey, as DPF regeneration can use a fair bit of oil.
Some questions and answers that may help;
Question: The glow plug symbol is flashing. Why? What
should be done?
Answer: The DPF regeneration has not been completed during
normal driving and now DPF has reached its maximum saturation at which it can
still be regenerated. The limit value depends on variant and Model Year, but is
in the range of 105% - 125%.Possible causes for this are:
a.) Frequent short distance journeys, i.e. high soot
loading while at the same time regeneration of the DPF does not take place
because the conditions necessary were not fulfilled.
b.) Frequent interrupted regenerations, i.e. the engine was
switched off during regeneration. Applies to short journey drivers who have at
least fulfilled the conditions for triggering regeneration. If the glow plug
light flashes, the vehicle
a.) Engine running since start for longer than 2 minutes.
b.) Calculated saturation higher than 80%.
c.) Coolant temperature over 70°C for at least 2 minutes.
d.) No DPF-relevant faults stored in system.
e.) A defined vehicle speed threshold must have been
exceeded (e.g. for >80% loading, 100 km/h)
Question: Under what conditions is regeneration
interrupted/ended once it has started?
Answer: Normally when regeneration has been successfully
completed, or:
a.) After a maximum regeneration time (20 - 25 min.).
b.) If the engine is switched off or has stalled.
c.) If the engine is left idling for a long time (5 - 10
min.).
d.) If 1000°C is detected by the exhaust temperature
sensor.
e.) If during regeneration, a fault is detected on the
components relevant for combustion (injection/intake system).
If a regeneration is interrupted once started but before
it has been 50% completed, the glow plug lamp flashes on the next engine start
(cold or hot) and regeneration begins again once the operating conditions (see
3) have been fulfilled.
Question: How long does complete regeneration take? a.) In
the most favourable case? b.) In the least favourable case?
Answer: a.) Under constant conditions, i.e. the exhaust
temperature necessary for regeneration always lies above the required value, for
example during motorway/cross-country driving, the average regeneration time is
10 minutes.
b.) Vehicle conditions such as long down-hill descents,
frequent driving in the low-load range (city driving, idling) allow the exhaust
temperature to fall. If the conditions for triggering regeneration were
fulfilled, the active regeneration time can be extended up to 25 minutes
(depending on engine type). If complete regeneration is not possible within this
period, the regeneration will be interrupted.
Question: How does regeneration affect the oil life?
Answer: On each regeneration or attempted regeneration, a
certain diesel fuel amount is injected into the engine oil which reduces the oil
life. If the "INSP" light in the instrument cluster comes on, the engine oil is
exhausted and must be changed. Failure to do so could damage the engine.
MPG DPF regeneration will drastically effect fuel ecomomy. We have customers complaining of excesive fuel use with warning lights illuminated.
Euro 5 diesel cars... Fitted with Diesel particulate filters should stop being sold to customers who only do short town-city runs, the cost of filter replacement due to non completed regeneration is unfair. Customers just don't understand the process... If passive regeneration is possible when the car is stationary, i.e. part of the exhaust heats up to above 600 Celsius. I am just waiting for someone to get burned to death sitting in a traffic jam. I recently took the time to read a customers owners handbook supplied with a new car, very little mention of the DPF and definetly no safety warning about parking on dry grass fields with the engine running.
Page updated 28-05-18