If you've been wondering how to delete def system on 6.7 cummins, chances are you're tired of your truck constantly yelling at you about exhaust fluid levels or threatening to go into limp mode. It's a common frustration. The 6.7 Cummins is a workhorse—arguably one of the best diesel engines ever made—but the emissions equipment tacked onto it since 2007.5 and 2013 (when DEF became standard) can feel like a leash on a greyhound.
Let's be real for a second: most guys aren't looking to delete their trucks just to blow smoke or be a nuisance. They do it because they want their truck to actually start in the morning without a "Service Exhaust System" message popping up. They want better fuel economy, and they want the engine to last 500,000 miles without choking on its own soot.
Why people choose to delete
Before we get into the nuts and bolts, it's worth looking at why this is such a popular move. The DEF (Diesel Exhaust Fluid) system, along with the DPF (Diesel Particulate Filter) and EGR (Exhaust Gas Recirculation), are designed to lower tailpipe emissions. On paper, it's great. In the real world, it's a lot of moving parts that fail.
The EGR valve pumps hot, dirty soot back into your intake. Imagine if you had to run a marathon while breathing through a straw that was occasionally dipped in charcoal dust. That's what your Cummins is doing. Eventually, that soot builds up, the sensors get wonky, and suddenly your $70,000 truck won't go over 5 miles per hour because the computer is "unhappy." Deleting the system removes those failure points.
What you'll need to get started
You can't just crawl under there with a hacksaw and call it a day. If you do that, the truck's ECM (Engine Control Module) will freak out and stay in limp mode forever. You need a two-pronged approach: software and hardware.
First, you need a tuner. This is the most important part of knowing how to delete def system on 6.7 cummins. The tuner "reflashes" the truck's brain to tell it that the sensors are no longer there and that it doesn't need to perform a "regen" cycle anymore. Popular options usually include things like the EZ LYNK, MM3, or older RaceME tuners.
Second, you need the delete pipe. This replaces the massive, heavy canisters under your truck (the DPF and the SCR catalyst). You can go with a full 4-inch or 5-inch turbo-back exhaust, or just a "test pipe" that replaces the specific emissions sections.
Step 1: The Tuning (Do this first!)
The golden rule of deleting a 6.7 Cummins is to install the tune before you touch a single bolt on the exhaust. Why? Because if for some reason your tuner doesn't work or the file is corrupted, you still have a running truck. If you rip the exhaust off first and the tuner fails, you're stuck with a very loud, non-running lawn ornament.
Plug your tuner into the OBDII port under the dash. Follow the prompts to "read" the vehicle and then "write" the new delete-capable tune. This process usually takes about 10 to 20 minutes. Once it's done, the truck's computer will no longer be looking for DEF fluid levels or exhaust pressure readings.
Step 2: Removing the DPF and SCR
Now comes the muscle work. You're going to want to get under the truck and start soaking every bolt you see in penetrating oil. Exhaust bolts are notorious for rusting solid thanks to all that heat.
There are several sensors plugged into the DPF (the big boxy part of the exhaust). You'll need to unplug the EGT (Exhaust Gas Temperature) sensors and the NOx sensors. You don't necessarily need to save them, but it's a good idea to be careful just in case you ever have to put the stock stuff back on—which, depending on where you live, might be a reality during inspection time.
Once the sensors are out of the way, unbolt the flanges. You might need a buddy to help you here. That factory DPF/SCR assembly is surprisingly heavy—usually over 80 pounds. Once it's out, you can bolt in your new straight pipe. Make sure your hangers are secure and nothing is rubbing against the frame or transmission.
Step 3: Dealing with the DEF Tank
Once the exhaust is done, the DEF tank itself is basically just dead weight. Some guys choose to leave it there because it's a pain to remove, but if you want to save some weight and clean up the look of the underside, you can drop the tank.
Just remember to unplug the pump and heater wires and zip-tie them up high out of the way. You should also cap off the lines so dirt and moisture don't get into the electrical connectors. Since the tuner has deactivated the system, you won't get any lights on the dash for doing this.
Step 4: The EGR Delete (Optional but Recommended)
While we're talking about how to delete def system on 6.7 cummins, we have to mention the EGR. The DEF system deals with the tailpipe, but the EGR deals with the engine's intake.
Most "full deletes" include an EGR block-off kit. This involves removing the EGR cooler—that long silver cylinder on the passenger side of the engine—and installing plates to block the exhaust manifold and the intake. This keeps your engine oil cleaner for longer and prevents that nasty soot from gunking up your valves. It also clears up a ton of space in the engine bay, making it way easier to work on the truck later.
What to expect after the delete
The first thing you'll notice is the sound. The 6.7 Cummins sounds incredible when it can actually breathe. You'll get that classic deep rumble and a lot more turbo whistle.
Performance-wise, the truck will feel "snappier." Without the DPF restricting the exhaust flow, the turbo can spool up much faster. Most guys see an immediate jump in fuel economy—usually 2 to 4 miles per gallon, depending on how heavy your right foot is.
But it's not all sunshine and rainbows. You need to be aware that your truck will now smell like a diesel. That "clean air" scent is gone, replaced by the traditional smell of a semi-truck. Also, if you've gone with a high-horsepower tune, you might see some black smoke if you floor it.
A quick word on the "Legal Stuff"
I'd be remiss if I didn't mention that deleting a truck is technically for "off-road use only" in the eyes of the law. The EPA has been cracking down on tuning companies and shops that perform these modifications. If you live in a state with strict emissions testing (like California or parts of Colorado), you won't pass an inspection with a deleted truck.
Always keep your stock parts. Don't sell them for scrap immediately. If you ever sell the truck to a dealership or move to a "strict" county, you might need to spend a weekend bolting all that heavy stuff back on.
Final Thoughts
Learning how to delete def system on 6.7 cummins is a bit of a rite of passage for many Dodge owners. It's about taking back control of a machine you spent a lot of money on. It's a straightforward process if you have the right tools and a bit of patience, but the most important thing is doing your research on the tuner you choose. The software is what makes the hardware work.
Once it's done, you've got a truck that's more reliable, more powerful, and significantly more fun to drive. Just be prepared for your neighbors to hear you coming a little more clearly than they did before!