The diesel particulate filter systems on these engines are poorly designed and prone to serious, ongoing problems. The diesel particulate filter (DPF) is a device designed to remove soot from the exhaust gas of the diesel engine. However, diesel particulate filters must be cleaned from time to time or they will block up.
Typical warning messages include: DPF light flashing or staying on and/or engine management light flashing or staying on.
When you first start the car these messages may display, which is okay as long as they go off again as soon as the engine starts. If the lights don’t go off, there’s a problem, quite possibly a big one. If the lights don’t go on at all, chances are, some bastard has disconnected something to hide the problem.
The particulate filter needs to be regularly cleaned or it will clog and stop working. The more clogged the filter becomes, the more difficult it is to clean.
The cleaning of the filter is known as ‘regeneration.’ Regeneration is simply a fancy name for burning off the soot from the filter. This soot gets burnt off due to the fact that exhaust systems (which exist to carry the leftover gases from the engine’s exploding fuel) naturally get very hot when you drive the car continuously for any length of time.
This ‘passive’ regeneration occurs continually, and will generally go unnoticed by the driver.
However, many drivers don’t go on long, uninterrupted high-speed journeys. In certain circumstances (e.g. after frequent short journeys or slow driving in congested areas), automatic regeneration may not occur. Therefore, the filter begins to clog.
When the engine computer (ECU) detects that the filter is more than 45% clogged, a second process starts, called ‘active regeneration’.
Active regeneration means that the ECU tells the injectors to squirt more fuel into the engine. Because diesel engines are controlled by the amount of fuel being injected, the injection of more fuel makes the engine run faster and hotter. The ECU keeps the engine running faster and hotter for about 5 – 10 minutes. This process will normally clean the filter.
However, if the process of active regeneration is interrupted (e.g., by finishing your trip before the process is complete), the filter may not be completely clean.
If unsuccessful, the ECU will try and repeat this process for a further 15 minutes. If the filter is still clogged, the DPF light on the driver display panel will then be lit.
If the owner is lucky, simply driving at a constant speed of at least 60 km/h for about 10 minutes will solve the problem.
If not, the vehicle’s dashboard will display messages indicating that there is an engine management fault and DPF fault. The engine will drop into ‘limp home’ mode, or, sometimes, break down entirely. At this point the vehicle will have to go to a garage to have the filter professionally cleaned, which won’t be cheap. Occasionally, the entire DPF filter will have to be replaced, which will be very expensive.
Please note that few of these problems were generally covered under warranty, because as far as Volkswagen is concerned, if your DPF system blocks up and fails, then you are the architect of your own misfortune.
Be aware, however, that Volkswagen’s DPF system doesn’t always work as claimed. Many owners complain that the DPF light will come on even when they have faithfully performed all their duties of driving the car at least 60 km/h for about 10 minutes. Or, these drivers often find that, although the DPF light may go out once they take a motorway trip, it will go back on again within a few days. This has made some drivers’ lives a misery.
These engines suffer from common problems caused by either minor component failure or poor maintenance. These problems include:
a) Fuel filters need regular replacement. These have an extremely fine internal mesh that clogs easily. If the filter clogs, the engine will start to lose power and/or misfire and/or drop into ‘limp home’ mode and/or cause the engine to break down entirely.
b) Engine electronics such as ECU, oxygen sensor, mass-airflow meter, exhaust pressure sensor, boost pressure sensor and camshaft position sensor often have a limited life. Typical symptoms are loss of power, erratic engine operation and poor fuel economy. Some vehicles will break down completely. These problems are really hard to diagnose without expert assistance.
c) The rear engine mount locating point breaks off. This locating point is a small, cast-iron ear with internal threads that the mount bolts into. The usual reason this location point breaks is either due to a vehicle collision or when a mechanic fails to properly tighten the three engine mounting bracket bolts during engine repairs, especially timing belt replacement. Without the rear mount, the engine, and therefore the car, is useless. There’s a repair kit that allows the block to be repaired without removal, but it does require that EGR cooler be removed and replaced in order to fit the repair kit.
http://www.dieselgeek.com/VW_cracked_engine_block_repair_bracket_s/1828.htm