VW Passat, Touareg, and Audi Q7 TDI DPF and Adblue FAQ

Introduction

This FAQ shows how the DPF diesel particulate filter works, DPF regeneration, and DPF clogging problems.  Adblue fluid and refill procedure, Adblue safety, and Adblue fluid storage are at the bottom.

For the TDI engine found in the Audi A3 TDI, VW Golf, and VW Jetta TDI, see the article specific to those engines in 1000q: 2.0L TDI engine DPF FAQ. The difference is that they don't use Adblue.

VW Touareg TDI, VW Passat TDI, and Audi Q7 TDI are shown but this FAQ can also apply to the BMW 335d, BMW X5 xDrive35d, Mercedes Benz GL, ML 320 or 350 BlueTec, E320 Bluetec, or any diesel car that has DPF or Adblue since they work the same. 

The reason the 2.0L TDI engine 2012+ VW Passat is included with the 3.0L engines is because they all use Adblue.

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Summary of the emissions system in Audi Q7 TDI and VW Touareg TDI, Passat TDI

There are four major components to the emissions system along with a bunch of sensors and an exhaust fluid tank.  The sensors are written into the engine management computer so if you delete the DPF or bypass the DPF with a DPF delete kit, it will set a check engine light and the car may not run correctly. The correct way to delete the DPF is to also change the computer programming.

The oxidation catalyst is basically the same catalytic converter that was found on older cars.  

Diesel Particulate Filters (DPF) catches particulates in the exhaust.  Particulates are most of the black soot that you may remember from older diesel trucks.  Because of the DPF and more advanced engine management, the tailpipe stays much cleaner than comparable cars.  To meet ever tightening emissions standards, they were first equipped in North America on the 2006 VW Touareg TDI V10.  Each cylinder bank got 1 DPF.  The only Touareg that didn't have one was the first year 2004 V10 engine.  The Touareg wasn't sold for model year 2005 so that VW could catch up to emissions regulations where they added the DPF for model year 2006.

The Adblue system pumps Adblue fluid to a special injector which sprays fluid into the exhaust stream where it's catalyzed in the last component, the NOx catalyst where it cleans up NOx emissions.  Because diesel engines run very lean (much more air than fuel) compared to gasoline engines, they can get better fuel economy.  However, the extra oxygen in the unburned air is also turned into NOx during combustion.  This system can cut NOx emissions by up to 80% which lets them be sold in all 50 states.  All Q7 and Touareg 2009 and later use these.  All North American Passat 2012 and later also uses these.

For more info on the 2009-2010 VW Touareg, see 1000q: 09-10 Touareg TDI buying guide.  For info on the new style 2011 Touareg, see 1000: 2011 Touareg TDI buying guide.  For info on the 2009-2011 Audi Q7 TDI, see 1000q: Audi Q7 buying guide.  For the 2012+ VW Passat, see 1000q: mk6 Passat TDI buying guide. Fitting the Adblue system in a smaller body is one of the delays in the Audi A4 TDI in the US and North America.

You must use only Ultra low sulfur diesel (ULSD)

The reason why older cars couldn't use a DPF is because the fuel in North America didn't meet the ULSD standards.  ULSD has 97% less sulfur in the fuel than the older fuel that you may still find for off road and industrial use and in Mexico.  The sulfur will quickly clog the DPF and cause damage to the catalysts.  Today, all pump fuel sold in the US and Canada is ULSD.  Even if the fuel pump doesn't have the sticker, the refineries have already switched over.  

The delay was partly because refineries didn't want to make fuel for cars that couldn't benefit from them and you couldn't sell cars that didn't have usable fuel.  Part of the problem with the early introduction of the DPF in Touareg is that not all fuel was ULSD in 2005 when the 2006 VW Touareg TDI started going on sale.  The other problem is that biodiesel may not work very well in Touareg or Q7 because of the emissions system operation and post combustion injection.

How the DPF filter works and how the Adblue fluid and NOx catalyst work

See this videos first.  The left video shows the emissions system.  Below right is another video showing the whole system and other stuff (Audi Q7 TDI shown but can also apply to Touareg and Passat).

The basic system routing is shown below. Below right is a closeup of the Adblue injector.  The oxidation catalyst is tucked close to the engine.

In the spliced pictured below you can see the DPF, NOx catalyst, and the Adblue fluid injector.  The lower left on this Touareg is the fuel tank.

audi q7 adblue system tankThe pictures above show a Touareg but the Audi Q7 TDI system is basically the same.  The Q7 has a dual Adblue tank and longer piping because of the longer body.  They might be tuned slightly differently for the different car weight/load but they use the same engine and the system already adjusts with engine load/rpm/etc., so I don't know for sure.  Below and right are thumbnail images of the Q7 system showing the dual tanks, click to enlarge.

The lines to the lower tank is why the Q7 needs to burp out a little air while filling it.  The upper tank is the active tank where you add fluid.  Excess fluid drips down to the lower tank.  The lower tank has a pump to move it back up to the active upper tank where the Adblue pump pressurizes the fluid for injection into the exhaust.
audi q7 tdi adblue tank

Whenever you add fluid to the Q7, you are supposed to do a sensor adaptation.  More details below.

Below is a thumbnail of the VW Passat TDI Adblue system. It serves the same function but has been adapted to fit the Passat.

The first step - the catalytic converter

The oxidation catalyst is used on older TDI as well.  It has to be close to the engine to heat up as fast as possible to a minimum working temperature of 250oC.  The energy is used with platinum and palladium catalysts to oxidize hydrocarbons and CO into water and CO2.  This is a pass-through filter, meaning that gasses and particulates travel through small tubes traveling the length of the filter.  If you hold it up to the light, you can see through it. 

The second step - the DPF

Unlike the first cat, the DPF filter is a blocked off filter.  Gasses can pass through the filter but particulates are trapped.  If you hold it up to the light, you can't see through it.  This is why the cars can pass the white handkerchief test.  They are made of silicon carbine with platinum and aluminum oxide catalysts.

As it filters particulates, the little tubes will fill up with soot and increase backpressure.  You want the lowest possible backpressure downstream of the turbo so DPF do decrease vehicle performance and efficiency.  Since they are federally required emissions devices and effectively remove lots of particulates, do not delete the DPF on your Touareg or Q7 TDI.   Below is an illustration showing typical DPF filter construction.

Active vs. passive DPF regeneration

Acceleration or heavier engine load burns more fuel which heats up the exhaust gas temperature (EGT).  When EGT are above 350oC, the DPF begins to passively self clean by oxidizing and burning out the trapped particulates.  When the car is coasting down or in short stop-go trips, EGT doesn't get hot enough and the filter can't burn out all the particulates.  This causes them to build up.

If the filter is loaded beyond 45% (or every 466-621 miles/750-1000 km), the backpressure sensors can tell that the filter is getting clogged and will tell the car's computer to start an active regeneration self clean cycle.  After the engine combusts all the fuel, the fuel injectors squirt some extra fuel into the engine cylinder which is instantly vaporized and travels to the first cat converter.  It oxidizes and raises EGT to around 600-650oC which provides the energy to clean out the DPF.  The big difference between the 3.0L DPF and 2.0L DPF found in Jetta/Golf/Audi A3 TDI is that the smaller engines use a DPF that is right against the engine and the first cat.  The 3.0L engine DPF is relatively far from the first catalytic converter.  It's not yet known 

During a regen cycle, the ECU raises boost slightly to make up for any difference in power and it may raise the idle rpm slightly.   If you interrupt an active regen cycle by shutting the engine off, it won't finish and should restart the next time regen conditions are met.

If the regen cycle is interrupted by shutting off the engine, previous cycles fail due to bad fuel, or soot loading reaches 50-55%, the car will to force a 15 minute regen cycle.  There is no dashboard light to show when the car is in active regen mode.  If it continues to be interrupted or fails, the DPF warning light on the dashboard (pictured right) will come on.  If that happens, drive at about 40 mph for at least 10 minutes in 4th or 5th gear at 2000RPM (Disclaimer: faster would be fine as long as you don't exceed the speed limit).

If your DPF light comes on (shown at top and below) and it's not clogged, the exhaust back pressure sensor or exhaust gas temperature sensor could be faulty.

At 75% loading, the glow plug light will also come on.  If it gets to this point, go to have the car serviced.  It's still possible to do a service regeneration, a manually started active DPF regen unless there is something wrong with the filter.

If clogging reaches 68 grams (3.0L engine) or 95%, you must remove the DPF from the car and manually clean it.  The reason it has to be manually cleaned is because all the oxidation will raise heat to the point where the filter can be damaged.  Clogging which is caused by your driving style or bad fuel is not covered by the car's warranty.  There is also a federal emissions warranty.  VW and Audi suggest inspection of the DPF at 120,000 miles.  Truck stops are used to cleaning DPF so I suggest cleaning vs. replacement.  The filters also contain precious metals.  Since it's right under the car, any repair shop should should be able to remove it but you can't drive the car without it.

DPF cleaning procedure and replacement interval

As stated before, I wouldn't buy a replacement DPF because of the cost.  I see no reason why the DPF cannot be removed and cleaned.  At worst, the metal housing might need to be cut open and rewelded to clean the core but I'm sure this would still be cheaper than buying a new one because of the precious metals.  This is also why catalytic converters are often stolen.  Cleaning is a common procedure for heavy duty trucks.  The min use of a heavy duty truck filter is 435,000 miles w/scheduled cleaning and maintenance according to the EPA.

The reason why the filters become clogged is because again, they are blocked off filters which trap particulates.  Pass through catalytic converters will let stuff pass through them.  DPF will trap all solids including things that weren't designed to be burned in the engine, like byproducts from low quality fuel, non combustibles from the normal burning of additives and tiny metal particles in the engine oil, or other.

Unlike the Jetta/Golf/Audi A3 TDI, the DPF in your Touareg or Q7 is right there and easy to reach.  In the other cars, the front subframe has to be lowered to remove it.

Volkswagen says that you're supposed to check the DPF at 120,000 miles for ash loading.  If it's OK, check it every 10,000 miles afterwards.  If it's replaced it's good for another 120,000 miles.  68 grams is the load limit for 3.0L engines.  Older 5.0L V10 Touareg had a scheduled replacement of every 120,000 miles.  Elsewhere it says to check the V10 DPFs at 60,000 miles and every 20,000 miles after that.

Audi says to check the DPF at 125,000 miles for ash loading.  If it has more than 68g of ash content it must be replaced.  Inspect it every 20,000 miles afterwards until it needs replacement.

How to check DPF filter clogging or loading on a Touareg TDI or Q7 TDI

Plug the VCDS cable into the OBD2 port and start the software.  You must have access to the dealership tools or the Ross tech VCDS tool (used to be called vag com).  Make sure the cable is plugged in all the way and the LED light is green.  Select the control modules and go to "Engine".  You'll see the screen below.  You want to look at values so click on "Meas. Blocks -08".

Set the first group to 100, the second to 101, and the third to 102 and you'll see the screen below.  The first number in group 100 is engine rpm.  I'm pretty certain the second is engine coolant temperature.  The third is a regen timer and the fourth is if the regen was aborted.  0=not aborted, 1= aborted.

In group 101, the fourth number is the regen status.  1= heating up.  10= regen in progress.  100= cooling down.

Group 102 number 1 is the temperature before the cat.  The second is the temperature before the DPF.

Continue reading on page 2 for

Adblue Fluid safety info

Adblue tank layout

and how to add Adblue fluid

 

If you have more questions or comments about Adblue or why a DPF delete or DPF bypass is illegal, feel free to ask in the myturbodiesel.com forums