TDI DPF FAQ, repair, cleaning, and pictures
Diesel particulate filter DPF FAQ - page 2 Continued from page 1, with DPF layout and design
For the VW Touareg TDI, Porsche Cayenne diesel, Audi Q7 TDI, Passat TDI, and Chevy Cruze diesel, see 1000q: DPF with Adblue FAQ page 1. There are substantial differences from the non-adblue emissions system.
Passive or active DPF regeneration symptoms and conditions
The passive regeneration occurs with no action taken by the car's computer. It occurs with higher sustained engine loads like freeway driving or fast acceleration onto the highway when exhaust gasses are hotter. These types of loads will produce exhaust gas temperatures (EGT) of about 350-500oC which thoroughly heat up and burn the DPF. If the car has only short stop-go trips, the exhaust doesn't have a chance to have a good passive burn off and will have more active regens or clog.
"Self Study Program 826803" has a good description of the processes involved, and which sensors are critical to management of the DPF regeneration.
The active regeneration "self clean" is conducted based on specified programming logic in the ECU. two models are maintained, and the first one to get to the trigger causes the active regeneration to run at the earliest opportunity. one model generates calculated soot, the other a value for measured soot. to back up these models, a distance of 466-621 miles (750-1000 kilometers), will cause the active regeneration. EGR is shut off and the fuel injectors squirt a little fuel into the engine cylinders after combustion (post combustion injection) that travels to the oxidation catalytic converter and oxidizes to raise EGT to around 600-650oC. The gasses travel to the DPF and burn up the trapped particulates. In this way, the soot is converted to mostly carbon dioxide and water, both clear gasses, which then get past the DPF and out the tail pipe. the minor parts of the collected soot which cannot be converted remains as ash in the filter.
During an active regen the car's computer also temporarily increases turbo boost about 2-4 psi to make up for any lost power. Idle engine rpm also goes up around 200 rpm on the 2.0L engine. A cycle lasts about 10 minutes and if you shut the engine off in the middle of an active DPF regen cycle, you'll hear the radiator fans in the front of the car running fast (even after the car is shut off) and you may smell a burning rubber type odor. It will resume once you exceed 38 mph after the next engine start (and the exhaust is warm enough).
about every third to fifth DPF regeneration cycle, the elevated temperatures continue for up to 20 minutes. this is to regenerate the SOx cat, and also gets the DPF extra clean.
If you interrupt it by shutting the engine off, the active regen cycle won't finish. There is normally no light or indicator to show when the car is doing an active DPF cycle. If the cycle was interrupted by engine shut off, it'll try again.
If either one of the soot level estimates maintaned in the engine computers reach 24 grams, the DPF warning light on the dashboard (pictured right) will be seen. 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). This is explained in the owners manual.
At 75% loading (40 grams of soot), the glow plug light and check engine will also come on. If you see the warning, go to have the car service or go to the dealer so they can explain the warning lights to you. It's still possible to do a service regeneration, a manually started active DPF regen.
In the 2.0L engine, the automatic active regen is blocked by the car's computer once DPF loading reaches 40 grams. The service regen must be manually initiated using the procedure below. .
If clogging reaches 95% (45 grams) it must be manually removed and cleaned since all that combustion could damage or melt the filter due to extreme heat and pose a fire risk. There's a chance the repair would not be covered by the car warranty (maybe the federal emissions warranty) if you ignored the warning light or if the clogging is caused by your driving style.
the computer uses two ways to estimate these soot levels, and pays attention to the highest one. it is possible to lie to the computers, and reset values, but to do so you should at least make sure one of the methods is lower than 45 grams of soot. any such tricking is at your own risk. the method is the same one used to reset the computers after installing a new or cleaned DPF.
Using biodiesel up to B100 with a 2009 or newer VW Jetta TDI, Golf TDI, or Audi A3 TDI
The newer common rail TDI engines (CRD) in VW Jetta TDI or other models with DPF will run as well on biodiesel as older TDI engines ran fine on biodiesel. However, using biodiesel has three main problems. During the post injection combustion, it can collect in the cylinder instead of vaporizing and raising the EGT to heat up the DPF, preventing normal active DPF regenerations. By not vaporizing, biodiesel works its way into the engine oil much more than diesel. Because biodiesel has a higher distillation and boiling point, once it's in the oil, it accumulates and dilutes the engine oil.
There's always greater engine oil dilution during a post combustion injection cycle but regular diesel can evaporate more easily than biodiesel out of the engine oil. Once it evaporates, it's recycled into the air intake by the crankcase ventilation system and consumed by the engine. Biodiesel accumulates because it doesn't evaporate as easily. At a 2008 biodiesel conference, a VW representative said the engine could tolerate up to 50% fuel mix in the oil but no more. (source) This level could be exceeded after 10,000 miles with just B5. B10 would definitely exceed this level.
Some possible solutions are to delete the DPF on your VW or Audi TDI or install a DPF bypass kit. The engine tuning must also be adjusted to account for the removal of post combustion injection of fuel and DPF removal. It might be possible to tune the post combustion injection to have bio produce the same results as regular diesel.
The future of DPF systems might substitute an extra injector in the exhaust to inject the post combustion fuel downstream of the engine instead of right in the engine cylinder. This type of system is required if the DPF is downstream of the Adblue or NOx catalyst. Modern systems which don't use post combustion injection at the engine use this type of injection. In fact, when TDI was first introduced to North America, the VW Passat TDI used a low pressure injector in the exhaust to burn up fuel in the catalyst. It was discontinued because it didn't work very well, see 1000q: VW Passat 5th injector for details. Technology has improved since 1994-1995 so it's possible this type of system might return. The main obstacle is additional complexity and cost vs. an extra squirt at the existing fuel injectors.
Trace metals in the biodiesel from processing can also accumulate and foul SCR catalysts. On Adblue equipped cars like the Touareg or Q7 TDI, (see below for a detailed system description), most contaminants will be trapped by the upstream DPF. The level of trace metals are also so small that the SCR should be more tolerant of contamination and last the "real" lifetime of the car, or over 400,000 miles.
For more basic information about biodiesel and VW, see 1000q: intro to biodiesel.
How to check DPF filter status on a VW TDI or Audi TDI (this section could use an update)
Plug the VCDS cable into the OBD2 port and start the software. The Ross tech VCDS tool or dealer tool is required to view this info. Click on "Engine" and you'll see the screen below.
Click on "Meas. Blocks" and select group 075. The 3rd number block is the particle filter load. You can also see the soot load in the screenshots below.
Manually starting an active DPF regen cycle (not an emergency DPF regeneration)
Shown below is the procedure to manually start an active DPF regeneration. This is not required under normal circumstances. Use VCDS to enter the engine module as shown earlier. Click on "Security Access" and enter the security code 12233. Go back to the screen below and click on "Long Adaptation".
Click "Up" or enter 13 in "Channel" to get to channel 13 - DPF Regeneration. The value for active regen is 0 for off. Enter 1 in the "New value" box highlighted below and click "Save". This will start the active regen. The test conditions are: the vehicle must be driven between 80-120 kilometers per hour and no shutting off the ignition.
The screenshots below show calculated and measured soot loading in the DPF before and after the last active regen. The right screen shows 0km since last regen because it just finished. Note - 2010 and later appear to have changed their electronics and as of this writing, VCDS software shows milliliters loading as 0 and never moves. Soot load calculated and measured also show 0. 2010 TDI don't have label files yet and because the values never move, I don't believe it shows any actual values in this screen.
Forcing an emergency DPF regeneration (at up to 95% clogging)
As stated earlier, do not attempt an emergency regen if loading is above 95%. For the 2.0L engine this is 45 grams. Enter the engine module as shown before. Ross tech VCDS shows the following procedure but it didn't work for me.
Enter "Coding II" instead of adaptation. Enable regeneration by entering 21295 and hit "do it". Go back to the engine module and enter "Meas. Blocks". Select both groups 070 and 075. Block 3 of group 70 is the timer. In group 75, block 1 is EGT before turbo, block 2 is EGT before DPF, block 3 is particle filter load, and block 4 is EGT after DPF. During the test, keep driving between 20-37 mph and keep engine RPM around 1500-2500.
DPF service interval and end of life from ash loading clogging
I would personally just keeping driving it until active or driver initiated regens don't work anymore or become so frequent that it bugs you into replacing or cleaning the DPF. Engine power will also feel low once the DPF is clogged. Since the DPF is a filter, as it becomes clogged the exhaust backpressure will increase to the point of the engine also losing efficiency. VW and Audi's recommendation is to replace the DPF once it's clogged but it's a common procedure to remove and clean the filters used with heavy duty trucks. As discussed earlier, several vendors provide cleaning services for VW/AUDI TDI 2.0 liter engines. cleaners report that the DPF light will be lit, despite low soot values, when the DPF needs to be cleaned or replaced. this is reported to happen somewhere from 240ml of ash and up. For the 2010 models and later, rebuilt DPFs are on the market for around $1000 or less, which may be a more attractive path than waiting for the filter to be cleaned. cleaning is around half the cost of a rebuilt DPF.
If you decide to remove the system due to clogging, you should pick up noticeable mpg gain if you delete it due to the increased effiency of the engine. Don't throw the deleted DPF out because it has precious metals inside. Below are the suggested service intervals for Volkswagen and Audi DPF systems.
VW: you're supposed to check it at 120,000 miles and check ash loading. If it's OK, check it every 10,000 miles afterwards. there is no identified method for these checks, except to pay attention to the soot and ash values, and make sure all the sensors are operating.
Remember there is a difference between soot which is collected, and converted to gasses, and the ash which remains and eventually will clog the filter. soot builds up to need active regenerations in a time span within several hundred miles, and the ash will build up over several hundred thousand miles.
it is critical to keep the sensors operating, to avoid expensive replacement before it is required. any check engine light needs to be followed up as soon as possible. without the sensors, the computer will be blind and will not perform the regenerations needed to convert soot to gasses, and the DPF will clog up well before its time.
Audi: check the DPF at 125,000 miles for ash loading. If it has more than 45 grams of ash it must be replaced. Inspect it every 20,000 miles afterwards until it needs replacement. Since the A3 TDI uses the same engine as the VWs, I don't know why the inspection isn't at 120k then every 10k afterwards like theirs.
Nitrogen oxide (NOx) catalytic converter (2.0 liter engines on VW Golf TDI, Jetta, and Audi A3)
This reduces NOx and sulfur, the stinky part of the exhaust. The amount of NOx generated and the effectiveness of the NOx converter is what separates Adblue systems found in the 3.0L TDI engine vs. the non Adblue systems. The smaller engines don't use Adblue because the NOx cat converter can handle the emissions generated and use an exhaust valve and EGR system for sufficient reduction. The larger engines use Adblue as a reducing agent to reduce all the NOx. The NOx catalyst is placed last so that the high EGT from the DPF has a chance to cool down a little. Unlike the DPF, it's a pass through converter and not a filter.
The engine converter acts in 2 modes: DeNOx and DeSOx. DeNOx captures NOx during cooler operation and burns it off during hotter operation. To burn it off, the air intake throttle and the exhaust valve partially close to reduce the amount of O2 available and to provide sufficient backpressure to the low pressure EGR. When the O2 sensor detects a rise in the reduction agents (HC, CO, and H2), the NOx are burned off and it returns to capturing NOx. You can view some data on the NOx converter in channel 18 of long adaptation using the procedure shown above. Details of the 3.0L catalyst are shown below since they use Adblue.
As a side note, the exhaust valve (shown below) is an electric motor and spring. the spring pushes back against the electric motor. Because the spring is on the outside of the shaft, it's possible road salts could rust the spring and cause problems over the life of the car. NOTE: In March 2013, VW issued an extended warranty on this part and has a new part number. See this thread in the forum for details.
DeSOx mode removes sulfur buildup which slowly deactivates the DeNOx mode by burning it away at about 620oC and is done at the end of a DPF regen. It's calculated from fuel consumption so non ULSD can result in excess sulfur in this component. The H2S converter reacts H2S formed during DeSOx mode completely into SO2. H2S is a colorless poison gas with a rotten egg odor. Don't remove the H2S converter. SO2 has a sulfur smell like a match which was just lit and can irritate the nose and eyes. Although the exhaust meets all emissions standards, don't inhale the exhaust gasses!
The H2S converter is visible in the picture below.
How to delete and bypass the DPF system in a Volkswagen Golf, Jetta, or JSW TDI
First, make sure to check and comply with any applicable emissions regulations regarding the DPF system and modifying the exhaust. See the TOS Agreement for the full legal disclaimer. It is a violation of the US clean air act, and similar Canadian laws to modify automotive emissions systems and drive on public highways. States and provinces also have laws against modifications, but enforcement is focused on high pollution and high population areas. Deleting the system will increase power and efficiency but you may not pass vehicle inspections without this system. Vendors and tuners will specify than any such modification are for off road use only. You can immediately tell if a TDI has a DPF or not because without the DPF, the tailpipe will have soot on the inside. (some DPFs will crack and also leak soot. this clogs the EGR system over time and indicates the DPF has to be replaced. With a good DPF, even after high miles, the inside of the tailpipe is clean. This means it makes even less particulates than almost all gasoline cars.
If you proceed to remove the DPF, you need an engine tune. Now that you've read the previous sections about how the system works, you can see the car will not run as intended without the system in place. The check engine light will immediately come on but the car will still run. One person who removed the system before getting the engine tuned reported that the bumper reflector light above the exhaust melted when the car tried to do a DPF regen without the system in place. The service manual says that the front subframe has to be lowered for clearance but according to ToeBall "Just undo the passenger side CV from the trans. Manual says the subframe needs to come out, it doesn't. You'll have to rotate the DPF as it comes out and pry up on the heat shield on the floorboard but it'll come out. I've already done two this way."
Here is my DIY article on DPF removal in the wiki-FAQ.
Here are some thumbnail pictures (click to enlarge) from ToeBall's downpipe and exhaust replacement. For more on DPF delete, see this thread in the forum. and this thread