Home > News > 4" DPF & CAT Delete Pipe Install: 2017-2023 Duramax L5P DIY Guide
4" DPF & CAT Delete Pipe Install: 2017-2023 Duramax L5P DIY Guide
The L5P Duramax is the most locked-down diesel GM ever built — and also the most powerful. From the factory it makes 445 hp and 910 lb-ft, but the E41-encrypted ECM, the cascading NOx sensor network, and a triple-layer emissions canister wedged under the cab work together to hold it back. The fix starts with a delete tune, and the most popular first hardware step is swapping the factory DPF/DOC/SCR brick for a straight mid-section pipe.
This guide walks through exactly what the 4" DPF & CAT Delete Race Pipe does, what it doesn’t do, what you need before you touch a wrench, and how to install it without creating twice the work for yourself.
What You’re Removing: The L5P Emissions Stack
Every 2017–2023 Silverado and Sierra 2500HD/3500HD with the 6.6L L5P leaves the factory with a full modern emissions stack bolted under the cab:
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DOC (Diesel Oxidation Catalyst): First-stage treatment that oxidizes unburned hydrocarbons and CO. Sits closest to the turbo, directly downstream of the downpipe.
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DPF (Diesel Particulate Filter): A dense ceramic honeycomb that traps soot particles. Requires active regeneration cycles — the ECM injects raw fuel into the exhaust stroke to burn the filter clean, which kills fuel economy, heat-soaks the turbo, and dilutes engine oil with unburned diesel.
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SCR (Selective Catalytic Reduction): Uses DEF (Diesel Exhaust Fluid) injected into the exhaust stream to break down NOx. Monitored by multiple NOx sensors and a DEF quality sensor. DEF tank heaters fail, DEF injectors crystallize, and DEF pumps seize — any one of these triggers a 55-mph limp-mode countdown on your dash with no override.
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EGR (Exhaust Gas Recirculation): Recirculates hot, sooty exhaust gas back into the intake to lower combustion temperatures. Over time this bakes carbon onto the intake valves, clogs the intake manifold, and when the EGR cooler cracks, coolant pours into the cylinders.
On a high-mileage L5P, the DPF ceramic substrate permanently loads with unburnable ash. No amount of active regen clears ash — the filter is done, and a replacement DPF from GM runs thousands.
Why the L5P Is Different from Every Other Duramax
GM introduced the L5P in 2017 with something no previous Duramax had: E41 ECM encryption. The E41 protocol locks the calibration file behind a security layer that standard handheld tuners cannot read or write. Plug a generic OBD2 device into an L5P and it sees a brick wall.
To flash a delete tune on a 2017–2023 L5P, you need one of two professional-grade platforms:
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EFILive FlashScan V2 with AutoCal V3: A licensed L5P operating system package that unlocks the ECM, reads the factory calibration, modifies emissions tables, and flashes the delete tune.
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HP Tuners MPVI3 with L5P credits: HP Tuners added L5P support with the MPVI3 interface and the appropriate credit pack. Same deal — professional hardware, licensed software, requires a tuner who knows how to build the calibration.
Budget $800–$1,200 for the tuner and tune portion. This is not optional. Installing hardware without a delete tune sends the L5P into limp mode — cascading DTCs from missing NOx sensors, DEF quality faults, and DPF pressure differential errors will lock the truck down.
What This Pipe Does — and What It Doesn’t Do
The TruckTok 4" DPF & CAT Delete Race Pipe (DP-0295, $290) is a mid-section replacement pipe — not a full exhaust system.
The three sections:
- Pipe #1 (downpipe section): Bolts to the turbine outlet flange at the turbo via a 4-bolt flange. Replaces the factory downpipe and the DOC/SCR canister assembly behind the turbo. Includes a transmission hanger bracket.
- Pipe #2 (mid-section): Connects Pipe #1 to Pipe #3 via slip-fit connections. Carries a hanger that slides into the factory rubber isolator.
- Pipe #3 (rear section): Connects to your factory rear tailpipe or muffler section at the back. Also has a hanger.
What it replaces:
- The factory DOC, DPF, and SCR canister assembly mounted under the cab
- The restrictive exhaust path through ceramic filtration media
What it connects to:
- Inlet side → bolts to the factory downpipe flange at the front
- Outlet side → bolts to your stock rear tailpipe section at the back
What it does NOT include:
- A downpipe (this is downstream of the factory turbo downpipe)
- A rear tailpipe or muffler section (reuses your factory rear exhaust)
- An EGR delete kit (separate assembly, separate job)
- A tuner or tuning credits (required separately)
This is the most popular first hardware purchase for an L5P delete because it removes the heaviest, most failure-prone piece of the system — the DPF brick — along with the restrictive factory downpipe, all in a single bolt-on kit.
Fitment note: Fits 2017–2023 6.6L Silverado & Sierra 2500HD/3500HD in all cab and bed configurations. Does not fit Cab & Chassis commercial models (3500/4500/5500).
Before You Touch a Wrench: The Tune Comes First
One additional note from a 2021 owner who tuned first, then deleted in stages: after the tune is flashed, the DEF system will automatically purge itself — the truck literally blows white DEF vapor out the exhaust for about a day while it dumps the entire DEF tank. By the time you’re ready to pull the DPF, the DEF tank is already empty and the system has disabled itself. The tune is doing its job before you ever pick up a wrench.
For 2017–2023 (E41) trucks, the sequence is:
- Purchase your tuner device (EFILive or HP Tuners) and tuning package
- Work with your remote tuner to unlock the ECM, read the factory calibration, and receive the custom delete tune file
- Flash the delete tune to the truck via the OBD2 port — this disables DPF regen logic, DEF/SCR sensor faults, and EGR control tables
- Key the truck on and verify no immediate fault codes
- Now you can start removing hardware
If you’re doing this job in stages over a weekend, here’s a time-saving fact confirmed by multiple installers: once the delete tune is flashed, the truck can be started and moved with the exhaust partially or fully removed. It’ll be loud and the open downpipe will sound like a tractor, but it’s mechanically safe for short moves — in and out of the garage, onto ramps, repositioning in the driveway. Just don’t drive it on the street without the pipe connected — open exhaust dumping under the cab is a fire hazard.
The tune is the foundation. The hardware is the finishing touch. Get the sequence backwards and you add days of unnecessary work.
Tools and Materials
The pipe itself bolts in with basic hand tools, but getting the factory exhaust out is where the real work lives. Based on multiple L5P installs documented on video, here’s what you’ll need:
| Tool | Why |
|---|---|
| 15mm socket + ratchet | Downpipe flange bolts, exhaust clamp hardware |
| 13mm socket (deep and standard) | Various sensor bracket bolts, hanger hardware |
| 10mm socket | Heat shield bolts on exhaust components |
| 3/8" ratchet + extensions | Tight access around the firewall and transmission tunnel |
| Sawzall with extra-long blades (12") + spare blades | The factory DPF/DOC canister is double-walled and heavy. Cutting it into sections is the only reliable way to get it out without lifting the cab. |
| Angle grinder with cutoff wheel | Backup for places the sawzall can’t reach, especially the DOC section near the turbo |
| Floor jack | Jack the cab up slightly on the passenger side to clear the DOC behind the turbo. |
| Jack stands | Support the truck securely. You’re working under a heavy truck in tight quarters. |
| Penetrating oil (PB Blaster or similar) | Factory exhaust bolts and hanger hardware on a truck with miles will be rusted solid. Spray every bolt and flange the night before you plan to work. |
| Pry bar | Separating exhaust hangers from rubber isolators. |
| Safety glasses + gloves + ear protection | Cutting double-wall stainless with a sawzall at close range under the truck |
Step-by-Step Installation
Follow these steps to install your new TruckTok 4" DPF & CAT Delete Race Pipe:
Step 1: Disconnect All Sensors from the Exhaust
Before any cutting or unbolting, disconnect every sensor plugged into the DPF/DOC/SCR assembly:
- EGT sensors (temperature probes at multiple points along the exhaust)
- NOx sensors (upstream and downstream of the SCR)
- DEF injector connector and DEF fluid line
- DPF pressure differential sensor lines
- Any O2 or particulate matter sensors specific to your model year
Tie the loose connectors up to the frame with zip ties so they don’t hang or drag during the next steps. You’ll be installing CAN BUS termination plugs on these connectors later.
Remove all sensors from the exhaust pipe.
Loosen the flange securing the drain pipe and DPF/exhaust pipe assembly.
Step 2: Drop the Factory DPF/DOC/SCR Assembly
This is the most physically demanding part of the job. The factory emissions canister is heavy, awkwardly shaped, and wedged between the transmission and the frame rail on the passenger side.
Method that works (confirmed by multiple installers):
- Remove the transmission crossmember. This opens up the tunnel and gives you the vertical clearance needed to maneuver the canister out. Support the transmission with a floor jack before unbolting the crossmember.
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Remove the exhaust hanger bracket mounted to the passenger side of the transmission. This bracket traps the DOC upstream and prevents it from sliding rearward.
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Jack the cab up slightly on the passenger side. A floor jack under the cab mount, lift just enough to gain an extra inch or two of clearance between the firewall and the turbo — this is what lets the DOC section slip out.
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Cut the exhaust in two to three places. The factory assembly is double-walled stainless steel and will not come out in one piece without removing the cab. Use a sawzall with a 12-inch blade:
- First cut: behind the SCR canister, near the rear flange
- Second cut: at the weld seam between the DPF and DOC sections
- If needed, a third cut: the DOC section near the turbo outlet
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Remove each section individually. The rear section usually slides out first. The DOC section requires the most finesse — the jacked cab and removed crossmember together give you just enough room to work it free.
PRO TIP: Cover everything below the cut zone with a welding blanket or heavy cardboard before running the sawzall. Hot metal chips will embed themselves in anything nearby — fuel lines, wiring, your arms.
Step 3: Remove the Factory Downpipe and Inspect Flanges
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Remove the hanger bracket attached to the transmission — this bracket secures the factory downpipe and blocks the DOC from sliding rearward.
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Unbolt the 4-bolt flange that connects the factory downpipe to the turbine straight pipe. Use a 15mm socket. Save the OEM nuts — they’ll be reused with Pipe #1.
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Cut the factory downpipe inlet to free it from the tight space near the turbo. A sawzall cut here lets you drop the downpipe without pulling the turbo.
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Clean the turbine outlet flange face with a wire brush. Check for rust, warping, or damage — Pipe #1’s 4-bolt flange bolts directly to this surface.
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Inspect the rear tailpipe inlet where Pipe #3 will connect. Same process — wire brush, check for flatness and corrosion.
Step 4: Install the 3-Piece Race Pipe
The DP-0295 kit assembles in three sections, front to rear:
Install Pipe #1 (downpipe section):
- Position Pipe #1 so its 4-bolt flange lines up with the turbine straight pipe outlet at the turbo.
- Reuse the OEM nuts you saved from Step 3. Hand-tighten all four bolts — leave them loose so Pipe #1 can shift during alignment.
- Bolt the transmission hanger bracket back into place to secure Pipe #1’s position.
Install Pipe #2 (mid-section):
- Slide the sloped end of Pipe #2 into the tail end of Pipe #1. The slip-fit connection should seat fully.
- Slide the hanger on Pipe #2 into the factory rubber isolator mount.
- Leave the clamp loose — you’ll tighten everything in sequence in Step 5.
Install Pipe #3 (rear section):
- Measure the gap between Pipe #2’s outlet and the factory tailpipe inlet. Pipe #3 may need to be cut from its sloped end to match the exact distance — measure twice before cutting.
- Slide Pipe #3 into position and seat both slip-fit connections.
Final fitment check: Walk the entire system front to rear. Verify:
- Pipe #1 clears the firewall and transmission tunnel
- Pipe #2’s hanger sits in the rubber isolator without binding
- Pipe #3 aligns with the factory tailpipe inlet
- No section contacts the frame rails, crossmembers, or transmission housing
Step 5: Tighten the System From Front to Rear
- Start at Pipe #1: Torque the 4-bolt turbo flange in a crisscross pattern. OEM torque spec for these flange bolts is typically 30–35 ft-lbs — verify with your tuner or kit instructions.
- Tighten the V-band or slip-fit clamp between Pipe #1 and Pipe #2. Get it snug — these clamps hold under exhaust pressure and vibration and need to be mechanically tight, not just hand-tight.
- Tighten the clamp between Pipe #2 and Pipe #3.
- Check all clamps for even gap around the pipe circumference. A clamp that’s tight on one side but loose on the other will leak.
- Reinstall the transmission crossmember and torque the crossmember bolts to factory spec.
- Lower the cab if you jacked it up. Remove the floor jack.
Step 6: Install CAN BUS Termination Plugs
This step is unique to the L5P platform and is not optional on 2017–2023 trucks. The J1939 CAN BUS network uses termination resistors at each end of the data line. When you unplug the NOx sensors, DEF quality sensor, and other emissions-related modules, you break the network termination — which triggers persistent ghost fault codes that won’t clear with a scan tool.
Note: connector styles changed between model years — 2017–2019 L5Ps use a 4-piece plug set with a different pin layout than the 2020–2023 trucks. Make sure you order the correct year range kit.
- NOx sensors (upstream and downstream)
- DEF tank level/quality sensor
- DEF injector connector
- EGT probes (typically 4–5 on an L5P)
- PM (particulate matter) sensor if equipped
- Throttle valve connector (this stays permanently unplugged after a delete tune — do not reconnect it)
Once all plugs are installed, use your tuner’s code-clearing function to remove any legacy DTCs. A brief check-engine light on first startup after flashing is normal — the ECM is re-learning the sensor network state.
Step 7: Verify No Leaks, No Codes
- Start the engine and let it idle. Listen for exhaust leaks at the turbo flange and at each slip-fit clamp junction — a sharp ticking or puffing sound means a clamp isn’t tight or a flange gasket isn’t seated.
- Watch for check-engine lights. A persistent light means a sensor wasn’t properly terminated or a code wasn’t cleared during the tune flash.
- Take the truck for a 20–30 minute test drive. Vary load — light cruising, moderate acceleration, a brief highway pull. Monitor EGTs, boost, and any return of fault codes through your tuner’s live data display.
- After the drive, let the truck cool completely, then re-check torque on the turbo flange bolts and all slip-fit clamps. Thermal cycling from the first hot run settles the hardware — a re-torque after the first heat cycle prevents leaks that show up days later.
Companion Upgrades That Make the Delete Complete
The DPF delete pipe removes the single heaviest restriction in the exhaust. But a full delete addresses all three emissions systems — exhaust, EGR, and crankcase ventilation. Here is what to pair with your race pipe for a complete build:
EGR Delete Kit
Deleting the DPF without deleting the EGR leaves hot, dry soot recirculating into your intake — cleaner than the EGR+carbon slurry a stock truck produces, but still not ideal. The EGR cooler on the L5P is also a known failure point: when the internal welds crack, coolant dumps directly into the cylinders. A hydro-locked L5P is a rebuild, not a repair.
TCM Transmission Tuning
The factory Allison 6-speed and 10-speed TCMs are calibrated for stock torque levels. Once you delete the DPF, remove exhaust backpressure, and flash a performance tune, the transmission’s clutch packs are dealing with significantly more low-end torque. The factory TCM calibration will slip under the new load.
TruckTok’s L5P TCM Tuning Package includes the TCM unlock, 4 HP Tuners credits, and a custom calibration that increases line pressure, optimizes shift points, and improves torque converter lockup — exactly what the Allison needs to hold the additional power.
CCV Reroute Kit
The factory CCV (Crankcase Ventilation) system dumps sticky oil mist into the intake tract, where it coats turbo compressor blades and pools in the intercooler. A CCV reroute kit replaces the factory CCV plumbing with a vent-to-atmosphere setup — billet aluminum block-off plate on the intake side, heavy-duty silicone hose routing crankcase vapor away from the intake. On a CP4 truck that sludge is a ticking time bomb. This reroute kit is cheap insurance.
Performance Notes
Numbers below reflect a full delete+tune build — pipe, EGR delete, and custom ECM calibration together:
| Metric | Stock L5P | Full Delete + Tune |
|---|---|---|
| Horsepower | 445 hp (factory rated) | 500–550 hp at the wheels |
| Torque | 910 lb-ft (factory rated) | 1,000–1,100+ lb-ft |
| Fuel economy (highway) | 14–17 MPG | 17–21 MPG |
| EGT under heavy tow | Elevated, ECM-managed | 150–200°F cooler |
| Turbo spool | Restricted by DPF backpressure | Noticeably faster |
The horsepower and torque gains come from the delete tune removing factory torque limits and advancing injection timing. The pipe removes the physical DPF/SCR restriction so the engine can actually flow that power to the tailpipe. The fuel economy gains come primarily from eliminating active regeneration — every regen cycle burns diesel for zero forward motion.
Conclusion
At TruckTok, we’re committed to providing top-notch products and support. If you run into any issues during installation, don’t hesitate to reach out:
The TruckTok 4" DPF & CAT Delete Race Pipe is the ultimate performance upgrade for your 2017-2023 Duramax L5P. Whether you’re hitting the track or tackling off-road adventures, this pipe delivers unmatched flow and power.
Click here to order yours now! Upgrade Your Duramax Today!
Disclaimer: This product is for off-road and racing use only. Installation on vehicles driven on public highways may violate federal, state, or local laws. TruckTok is not responsible for any legal issues arising from improper use. Always comply with local regulations.
Frequently Asked Questions
Q1: Is deleting the DPF on an L5P street legal?
No. Removing or disabling emissions equipment on a vehicle driven on public roads violates the Clean Air Act. This product is sold for off-road, competition, and closed-course use exclusively. Penalties can include fines up to $5,000 for individuals.
Q2: Can I install this pipe without a tune?
Absolutely not. The L5P ECM monitors every sensor in the emissions system continuously. Removing the DPF, DOC, and SCR without a delete tune will trigger cascading DTCs, limp mode, and a DEF countdown you cannot clear. The tune disables DPF regeneration logic, DEF/SCR sensor monitoring, and EGR control — it must be flashed before you start the engine after deleting hardware.
Q3: Does this pipe replace the entire exhaust system?
No. DP-0295 is a downpipe-back system — three sections that replace the factory downpipe, DOC, DPF, and SCR from the turbo outlet to the tailpipe connection. Your factory rear tailpipe and muffler section remain in place and connect to Pipe #3’s outlet. If you want a full turbo-back system including the rear exhaust, you need a separate rear tailpipe section in addition to this kit.
Q4: Do I need CAN BUS plugs for a 2017–2023 L5P?
Yes. The J1939 network on the L5P requires proper termination. Leaving NOx sensor, DEF quality sensor, and EGT probe connectors open after deleting will produce persistent ghost codes. CAN BUS termination plugs with the correct 120-ohm resistor fix the network and let the ECM run cleanly after the tune.
Q5: What is the total cost of an L5P delete?
Hardware: the DPF/CAT delete pipe ($290) plus an EGR delete kit ($200–$400) and CAN BUS plugs ($100–$150) totals roughly $600–$850. Tuning: the tuner device, credits, and custom calibration run $800–$1,200. A complete DIY build lands around $1,500–$2,100 in parts and tuning. Professional installation labor (6–10 hours) adds $600–$1,500 at typical diesel shop rates.
Q6: How long does the physical pipe install take?
For a first-time DIYer with a jack, stands, and a sawzall: budget 4–6 hours. The factory exhaust extraction is the bottleneck — cutting the canister into manageable sections and clearing the DOC from behind the turbo takes patience. If you have a lift and experience, this is a 2–3 hour job.
Q7: Will a dealer know the truck was deleted if I return it to stock?
Yes. The ECM stores a flash counter that increments every time the calibration is written. Even if you re-flash the factory tune and reinstall all factory hardware, the flash counter shows the ECM was modified. GM dealers can and do check this for warranty claims.
Q8: What happens to the exposed wiring connectors under the truck?
You must seal every disconnected connector. CAN BUS termination plugs serve this purpose for network-connected sensors, but any connector not using a CAN plug should be sealed with a weatherproof cap or a tuner harness plug kit. Leaving connectors open to road salt, mud, and water corrodes the pins and eventually shorts the wiring — and those harness sections are expensive to replace.