Many scenarios can result in the need to tell if a DPF has been removed. A common scenario is where you have purchased a truck but are suspicious about the presence or absence of DPF since the seller may have failed to disclose its status. This could be the case if it’s fairly typical for people to delete the DPF (where you live) and then anxiously await their annual inspection, praying they’ll pass the emissions test.
Moreover, if you do your own repairs and have started with a small oil change but don’t want to ruin your vehicle, your choice of engine oil, to some extent, will depend on whether the DPF has been deleted or not. Thus, it helps to be aware of the DPF status in your vehicle to stay guided. Besides, it is not even legal not to have one.
How Can You Tell if a DPF Has Been Removed?
1. Check with a Piece of Cloth
To check for a DPF, grab a piece of cloth and place it on your exhaust pipe, then have someone rev the engine. If the cloth turns completely black, then there is no DPF. If the DPF is in good condition and the car has around 50k miles on the odometer, you could stick your finger in the exhaust pipe and it should come out clean. With a DPF delete, you will be able to hear your turbo whistle and see some black soot clouds when accelerating hard.
Meanwhile, track car oils, or oils used in cars without a DPF, have a high zinc content and could poison and clog a DPF. Similarly, cheap semi-synthetic oils that produce a lot of ash when burned could clog a DPF quicker, leading to more frequent regenerations and reducing the lifespan of the DPF.
There’s a chance you might not even need a cloth, as your exhaust might already appear quite sooty. You might notice black clouds during hard acceleration, but that could be due to the car being chip-tuned by the previous owner and it’s spitting oil.
2. Turbo Whistle and Diesel Smell
Another way to tell if a DPF has been removed could be the presence of a turbo whistle and a diesel smell. These are often more noticeable when the DPF has been removed.
3. Check the Service Menu
Some vehicles may have a particle filter option in the service menu on the iDrive. If this option is missing, it could suggest that the DPF has been removed.
4. Use Diagnostic Software
You can also use diagnostic software like Rheingold to check the pressure in the DPF at different RPMs. If the pressure is consistently zero, it could indicate that the DPF has been removed.
You could use a diagnostic tool like VCDS (VAG-COM Diagnostic System) to check the ash mass content or soot level. If the DPF has been deleted, the ash mass/soot level will be 0%.
5. Run a Physical Inspection
You can tell if a DPF has been removed through a physical inspection of the vehicle. This involves getting the vehicle in the air and removing the under trays to check if the DPF has been removed or gutted. You may require professional assistance for this or get the car up on a ramp to visually inspect the exhaust system.
The DPF, typically located in the exhaust system under the vehicle, resembles a small muffler or catalytic converter. If you notice a straight pipe instead of the DPF, it has likely been removed. However, some people hollow out the DPF casing and leave it in place, making it appear as if the DPF is still intact, so, supplement your visual inspection with other checks to verify.
6. DPF Light Behavior
According to experts, one of the signs of a DPF delete is the behavior of the DPF light on the dashboard. Some people have reported that even after DPF removal, the DPF light still comes on for a split second when the ignition is turned on. However, it should not come on while driving, indicating a need for regeneration, if the DPF has been properly removed.
7. Check for Regeneration
If you’ve never seen your car attempt a regeneration (a process where the DPF cleans itself by burning off the accumulated soot), it could be the sign you need to tell if a DPF has been removed.
8. Increased Noise
The DPF also serves as a silencer in the exhaust system. If it has been removed, there may be an increase in exhaust noise, particularly noticeable during hard acceleration. This change in noise level can be a strong indicator of a missing DPF.
9. Check Engine Light
Modern vehicles come equipped with sensors that monitor the DPF’s status. If the DPF has been removed, these sensors may detect an anomaly and trigger the check engine light. However, this light can also be activated by numerous other issues, so it is seen better to have the vehicle scanned for error codes to confirm the cause.
10. Decreased Fuel Consumption
The DPF regeneration process, where accumulated soot is burned off, can increase fuel consumption. If the DPF has been removed, you might notice a decrease in fuel consumption. However, many other factors can affect fuel consumption, so this sign should be considered along with others.
11. Emissions Test Failure
In many areas, vehicles are required to undergo regular emissions tests. A vehicle without a DPF will likely fail these tests due to the increased particulate emissions. That is not to say that people don’t sometimes manage to pass emissions with a deleted diesel.
12. Have a Mechanic Do the Checking
If you’re still uncertain, a professional mechanic or emissions specialist can inspect the vehicle with expertise and tools. That way, they can accurately tell if a DPF has been removed.
13. Question the Previous Owner About DPF Modifications
You might consider reaching out to the previous owner to inquire about any modifications if you’re not equipped to inspect the car yourself.
If you bought the car from a dealership, bring it back and ask them for clarification. If the DPF has been removed, they shouldn’t have allowed you to take the car in the first place.
Is DPF Removal Reversible?
Yes, DPF removal is reversible. If a DPF has been removed from a vehicle, it can be reinstalled or replaced. However, this should be done by a professional mechanic to ensure it’s installed correctly and functioning as it should. If the original DPF has been physically altered or damaged (for example, if it was hollowed out), it will need to be replaced with a new one. DPFs are vehicle-specific, so the replacement must be the correct model for the vehicle.
After the DPF is reinstalled, the vehicle’s computer system may need to be reset or reprogrammed to recognize the DPF and operate it correctly. This process should also be done by a professional.
If your car has been operated for a significant amount of time without a DPF, there may be other issues you need to address. For example, the engine may be running in a state of tune that is not compatible with a functioning DPF, or other parts of the emissions system may have been damaged or altered.
Meanwhile, here is what you can do if caught with DPF delete.
Does Removing DPF Use More Fuel?
The Diesel Particulate Filter (DPF) helps in an emission process by trapping the soot particles system from the exhaust gases. However, it also requires periodic cleaning through a process called regeneration, which can increase fuel consumption during that period. The regeneration process burns off the accumulated soot in the DPF.
There are two types of regeneration including:
- Passive
- Active
Passive regeneration occurs naturally when the vehicle is running at high speeds for long periods, like on a highway. Active regeneration, on the other hand, is initiated by the engine control unit (ECU) when the DPF gets too full and the vehicle has not had a chance to do a passive regeneration. During active regeneration, extra fuel is injected into the engine to increase the exhaust temperature and burn off the soot in the DPF.
So, when the DPF is functioning correctly, there can be a slight increase in fuel consumption during the active regeneration phase. However, this is generally offset by the periods of normal driving between regenerations. If the DPF is removed, the vehicle will no longer go through the regeneration process, which leads to a slight decrease in fuel consumption.
Ultimately, removing the DPF is generally illegal due to the increase in harmful emissions, and figures show that more than 1,000 diesel cars have been caught without pollution filters. It can even cause other issues such as damage to the engine and exhaust system, and reduces the resale value of your car. If you successfully tell that a DPF has been removed from your truck, notify the dealer about it; they should have disclosed it in the first place.
