Table of Contents

How the L5P Aftertreatment System Works

GM's L5P aftertreatment stack runs several stages in series, and the DPF is one of them. The filter is a dense honeycomb substrate that traps soot. As it loads, exhaust backpressure climbs and the engine has to work harder to push exhaust out.

How regeneration actually happens

The L5P does not use in-cylinder post-injection to regenerate its DPF. It uses a dedicated hydrocarbon injector, often called the 9th injector, mounted in the exhaust downstream of the turbo and ahead of the oxidation catalyst. During an active regeneration, the ECM commands that injector to spray diesel directly into the exhaust stream, which raises exhaust temperature and burns off the trapped soot.

This matters because in-cylinder post-injection was how older platforms raised exhaust temperature, and that method can wash fuel past the piston rings into the oil. The L5P's exhaust-side injector keeps regeneration fuel out of the cylinders. That is why oil dilution is not the reason to delete a DPF on this truck.

What actually causes DPF problems

A DPF that keeps clogging is usually a symptom, not the root cause. Before you buy hardware, have a shop check:

  • Drive cycle. Short trips and heavy idling interrupt regenerations. A filter that never finishes a regen keeps building soot.
  • The 9th injector. It lives in the exhaust stream and can foul with soot. If it cannot deliver fuel, regeneration cannot reach the temperature it needs. GM uses code P20CB for the aftertreatment fuel injector circuit.
  • Sensors. The pressure and temperature sensors that report soot load can fail and send bad data.

If one of those is the real problem, a delete pipe removes the symptom and leaves the cause in place.

Pipe Options: 4-Inch vs 5-Inch

  4-inch 5-inch
Common use Daily drivers, tow rigs, work trucks Higher-power builds
Exhaust note Moderate Louder
Availability Listed for 2017 to 2019 and 2020 and newer Listed for 2017 to 2019

For most trucks, 4-inch is the practical choice. Step up to 5-inch only if your build justifies it and the size is listed for your year.

EngineGo also lists a 3.5-inch downpipe for 2017 to 2023 trucks. Check the L5P Duramax delete pipes collection for what is currently listed for your year.

Fitment: 2017 to 2019 vs 2020 and Newer

EngineGo lists L5P exhaust parts by these ranges:

  • 2017 to 2019: 4-inch and 5-inch downpipe-back systems, plus 3.5-inch downpipes.
  • 2020 and newer: 4-inch downpipe-back systems.
  • 2017 to 2023: combined EGR, DPF, and DOC delete kits.

The model ranges differ because the exhaust packaging changed and because tuning access differs. Confirm both the pipe and the tune are listed for your exact year before you order.

Delete Pipe or Full Kit?

  Delete pipe only Full kit
Covers The DPF section The DPF section plus EGR hardware
You still need A matching tune A matching tune, unless the listing includes one

A standalone pipe is only the hardware that replaces the filter. It does not include tuning and does not touch the EGR system. If your truck is already tuned and the EGR side is handled, the pipe alone can be the right call. If you are starting from a stock truck, compare the L5P Duramax delete kit listings so the parts match.

The Tune Is the Part You Cannot Skip

The L5P ECM watches the DPF through pressure and temperature inputs. Remove the filter without a matching calibration and the ECM sees hardware that is not there, sets codes, and commands regenerations that cannot finish. The truck can drop into reduced power.

EngineGo lists L5P tuning by build range, and the ranges do not all line up with the exhaust ranges. For 2017 to 2019 trucks, EngineGo's all-in-one listings pair the hardware with a Mini Maxx tuner. For 2020 and newer trucks, EngineGo lists an EGR and DPF kit with an EZ LYNK tuner. For 2024, contact us before ordering to confirm what is available. Our L5P tuner comparison walks through the platforms.

Line up the tune before installation day so you are not stuck with hardware you cannot calibrate.

Installation Notes

This is a job for someone comfortable under a heavy truck. Use a lift or rated jack stands.

  • Let the exhaust cool completely before you touch it.
  • Never work under a truck held by a jack alone.
  • Wear gloves and eye protection.
  • Support the aftertreatment assembly before you unbolt it. It is heavy.
  • Confirm clearance from the frame, fuel lines, and brake lines before you tighten everything.

If a factory bolt fights you, work slowly. Check each product page for the tools and hardware your kit requires. For the full walkthrough, see our L5P DPF delete guide.

Before You Buy Checklist

  • Confirm your model year, cab, and bed configuration.
  • Decide between 4-inch and 5-inch, and confirm the size is listed for your year.
  • Check what is in the box, including clamps and hardware.
  • Line up a matching tune before installation day.
  • Decide whether you need the pipe alone or a full kit.
  • Confirm your intended use is off-road, race, or non-public-road where permitted.

FAQs

Can I install an L5P DPF delete pipe without a tune?

No. The ECM will see the missing filter, set codes, and can reduce power. The pipe and a matching tune go together.

Will a delete pipe fit both 2017 to 2019 and 2020 and newer trucks?

Fitment differs by year, so confirm the pipe and the tune are both listed for your exact year.

Does an L5P DPF delete fix oil dilution?

Oil dilution is not the L5P's regeneration problem. The L5P sprays regeneration fuel into the exhaust through the 9th injector rather than into the cylinders, so it does not wash fuel past the rings the way older in-cylinder post-injection did. If your oil level is rising, have the fuel system checked.

Delete pipe or full kit?

Buy the pipe alone only if your truck is already tuned and the EGR side is handled. Otherwise a full kit keeps the parts matched.

Do I need to send my truck details before ordering?

It helps, especially if your truck is modified or sits between ranges. Send your year, model, engine, cab, bed, current exhaust setup, and prior modifications to cs@enginego.com.

Shipping and Returns

Most orders are processed the same or next business day, excluding Sundays, unless otherwise stated. Most packages are delivered within 3 to 5 business days after leaving the warehouse, depending on package size, location, and carrier conditions.

Returns are accepted within 45 calendar days of delivery on unused, uninstalled parts in original condition with all included hardware. Installed, modified, or damaged parts may not be returnable. Electronic parts and tuners may have stricter return limits, and kits that include a tuner may differ. Return shipping may be the customer's responsibility on returns for buyer's reasons. Contact us for an RMA before shipping anything back.

Next Step

Send us your year, cab, bed, and whether the truck is a dedicated off-road build. We will confirm which L5P pipe and tune fit before you order.