Table of Contents

Fitment: Check Before You Order

  • Trucks covered: 2011 to 2016 Silverado and Sierra 2500HD and 3500HD pickups with the 6.6L LML.
  • Not the same engine: The LMM (2007.5 to 2010) and L5P (2017 to 2023) use different hardware and tuning. Do not mix parts across generations.
  • Year-break warning: The turbo downpipe connection changed during the 2015 model year. Early trucks use a V-band clamp. 2015.5 and 2016 trucks use a 3-bolt flange. Some 2015 trucks sit on the line, so look at your downpipe before you order instead of relying on the model year alone.

Why LML Owners Look at Deleting

The LML carried the most complex emissions stack GM had put on a Duramax. The LMM before it ran a DPF and EGR. The LML added DEF and SCR on top of both, making it the first Duramax to need Diesel Exhaust Fluid. Three systems run at once, all supervised by the ECM.

Active regen sprays fuel into the exhaust to burn off soot, and owners notice the extra fuel use on long towing days. The bigger cost shows up at the shop. EGR cooler failures, DPF problems, DEF doser failures, and NOx sensor codes are all documented on this platform.

A delete removes the hardware behind those repairs. It does not make the truck bulletproof, and it does not touch the fuel system. We cover that gap below.

LML Emission System Overview

Knowing what you are removing explains why the kit has the parts it has.

EGR Cooler Failures

The EGR system routes exhaust gas back into the intake to lower combustion temperatures. The cooler uses engine coolant to pull that gas down to a usable temperature. The thin internal tubes take constant heat cycling, and they can crack, especially on trucks that tow often or run stop-and-go.

GM documents EGR cooler leaks as a cause of coolant loss on these engines. Pressure test the cooler before you buy parts. Our LML EGR cooler leak guide covers the test and the symptoms.

DPF and Regen Behavior

The DPF traps soot in a ceramic honeycomb. When it fills, the ECM starts an active regen. On the LML, a dedicated injector in the exhaust (the "9th injector") sprays fuel ahead of the oxidation catalyst, which pushes exhaust temperatures to roughly 1,000 to 1,300°F. A regen takes a while to finish, and the truck uses extra fuel the whole time.

One cheap check before you replace a DPF: watch your coolant temperature. A thermostat that lets the engine run cool can set its own code and can throw off regen behavior, so rule it out first.

If the codes keep coming back after that, read our guide to LML DPF codes and the 9th injector before you replace the filter.

DEF and SCR System

SCR is what separates the LML from earlier Duramax engines. DEF, a urea solution, is injected into the exhaust ahead of the SCR catalyst, where it reacts with NOx to form nitrogen and water. The system needs a DEF tank with heaters, heated lines, a pump, a doser, and NOx sensors on both sides of the catalyst.

Every one of those parts can fail. DEF freezes at 12°F, heaters and lines burn out, a leaking doser leaves crystallized deposits, and NOx sensors foul. When the system reports a fault and it is ignored, the truck eventually limits speed and power.

What a Complete LML Delete Kit Includes

A complete all-in-one diesel kit has to address all three systems and include matching calibration. Here is what to look for.

DPF Delete Pipe (4-Inch Fitment)

The delete pipe replaces the DPF and SCR canister assembly with a mandrel-bent stainless section. It removes the most restrictive part of the exhaust and is where most of the flow improvement comes from. Match the connection to your year:

  • 2011 to early 2015: V-band clamp at the turbo downpipe.
  • Late 2015 (2015.5) and 2016: 3-bolt flange.

Ordering the wrong connection is the most common mistake on an LML. A V-band pipe will not bolt to a 3-bolt truck without cutting and welding. Find the right DPF delete pipe for your exact year before you buy, and confirm the cab, bed, and exhaust routing on your truck.

EGR Block-Off Plates and Coolant Bypass

The LML EGR delete kit covers the EGR side of the job. It typically includes billet aluminum block-off plates for the EGR valve opening and cooler ports. You have two paths: remove the cooler entirely, or block off flow and leave the cooler in place. Full removal cleans up the engine bay and ends the coolant leak risk. Either way, the coolant circuit has to be completed correctly so the cooling system stays balanced and free of trapped air, which the ECM can misread as an overheating event.

DEF and SCR Delete Module

The DEF module handles the SCR hardware on the LML. Without matching calibration, the ECM will still set DEF faults and can derate the truck, so the module and the tune are a matched pair.

LML-Compatible Tuner

The tuner is the most important part of the kit. The LML uses a Bosch EDC17 ECM, which is sensitive to voltage drops during a flash and needs a device that communicates with both the engine ECM and the Allison TCM. A proper LML Duramax tuner is also where power and drivability come from, because the calibration, not the pipe, controls injection timing, pulse width, and boost. Our tuner comparison for LML and LMM trucks breaks down the options.

Many all-in-one kits ship with pre-loaded tunes at several power levels, so you can run a milder tune for daily driving and a stronger one for towing. Tuner and electrical items have stricter return terms, so read the product page before checkout.

What a Delete Does Not Fix: The CP4.2 Fuel Pump

The LML moved from the Bosch CP3 pump used on earlier Duramax engines to the CP4.2. The CP4.2 depends on fuel for lubrication, and U.S. ultra-low-sulfur diesel gives it less margin than European fuel. When a CP4.2 fails, it can send metal debris through the rails and into the injectors. A full repair can mean the pump, all eight injectors, both rails, the lines, and a fuel tank cleanout. Repair bills commonly run into five figures.

Deleting the DPF, EGR, and SCR does nothing to protect the CP4.2. If reliability is the goal, address the fuel system in the same build.

The usual fix is a CP3 conversion. S&S Diesel Motorsport makes a 50-state kit for the 2011 to 2016 LML that carries CARB Executive Order D-756 and needs no tuning changes. It is listed by S&S dealers at around $2,600 for the kit with pump, and it works on a truck with factory emissions equipment in place. Confirm current pricing and fitment with the seller.

LML vs L5P: Why the LML Is Easier to Tune

The LML's Bosch EDC17 has been mapped by the aftermarket for years. Flashing is straightforward through the OBD-II port, tuner hardware is mature, and community knowledge is deep. The L5P uses a more locked-down ECM, and early tuning often meant bench-flashing the module or buying an unlocked one, as covered in our 2017 to 2023 L5P overview. For LML owners that means more choices, lower entry cost, and easier support.

Allison 1000 Limits After Tuning

The Allison 1000 is one of the best factory transmissions in the segment, but it has a limit. Extra torque, heavy towing, and wheel hop put the most load on the C3 and C4 clutch packs. When they slip, fluid heats up fast, clamping pressure drops, and the TCM can set a P0700 and command limp mode.

A TCM tune that raises line pressure is the first line of defense. At higher power levels it is a stopgap, and sustained heavy use may call for a built converter, upgraded clutches, or reinforced internals. Budget for the driveline when you pick a tune level, and keep fluid and cooling in good shape.

Installation Notes

Difficulty and Time

A full LML delete (EGR, DPF pipe, DEF components, and tune) is a hard weekend job for an experienced owner with solid shop tools. Plan on a full day or more of wrenching. Use a lift or quality jack stands, let the exhaust cool completely, and wear eye and hand protection. If you are not comfortable under the truck, professional installation is the better call.

EGR Access

EGR access on the LML is tight. Full cooler removal means disconnecting coolant lines, pulling intake components, and unbolting the cooler from both the valve and the manifold. Drain and dispose of coolant properly. Our step-by-step LML EGR install guide walks through the job, and your kit includes model-specific instructions.

Tune Flash

Read and save your stock calibration file first, and follow your tuner's instructions for the order of work. Voltage drops are the main cause of failed flashes, so confirm your batteries are fully charged and switch off HVAC, lights, and the radio. The tuner talks to both the ECM and TCM, and a first flash typically takes 30 to 45 minutes.

What to Expect After the Install

Removing the DPF and SCR canisters lowers exhaust backpressure, which helps turbo spool and throttle response. The factory LML rating is 397 hp and 765 lb-ft. Any change from there comes from the calibration, and results vary with tune level, supporting parts, and fuel quality. We do not publish guaranteed horsepower or MPG figures, because they depend on your truck.

Towing is where owners notice the most change. Lower backpressure can bring exhaust temperatures down under load, and the truck no longer stops to run active regens. That removes a common source of mid-trip problems, but it does not remove the fuel pump or transmission risks above.

Legal and Compliance

Read this section before you order.

  • The Clean Air Act prohibits removing or disabling emissions controls on a vehicle certified for road use. It also prohibits selling and installing parts whose purpose is to defeat them.
  • EPA's enforcement position is that a certified road vehicle must stay in its certified configuration, even if it is used only for competition. The agency dropped explicit competition wording from its 2016 rule but has said it always held that authority, so do not count on a competition-only exemption.
  • Civil penalties apply per violation and are adjusted every year. A kit with several components can mean several violations on one truck, and enforcement reaches installers and sellers as well as owners. EPA made aftermarket defeat devices a national enforcement priority after estimating that more than 550,000 diesel pickups were tampered with between 2009 and 2020.
  • A deleted truck cannot meet state emissions inspection requirements. Inspections check OBD readiness monitors and, in many states, look for the factory DPF, SCR, and EGR hardware. That affects registration and resale.

EngineGo sells these products for off-road, race, or non-public-road use only. You are responsible for confirming federal, state, and local law before you buy or install. If you want to stay emissions-compliant, the CP3 conversion above and sensor, thermostat, or component repairs are the paths that keep the truck certified.

FAQs

Does an LML delete fix the CP4 fuel pump problem?

No. The delete removes emissions hardware. The CP4.2 is a separate weak point, and a failure can cost far more than the emissions repairs. Many LML owners plan a CP3 conversion alongside any other work.

Will this void my factory warranty?

The LML is 2011 to 2016, so it is past the factory powertrain warranty. Extended warranties and service contracts vary, and tampering can affect coverage. Read the terms of any active policy before you start.

Can I go back to stock after a delete?

Yes, if you keep all the factory hardware (DPF, EGR, DEF components) and your tuner can flash the original calibration back. Keep the removed parts and your stock file in a safe place.

What is the difference between 2011 to 2015 and 2015.5 to 2016 fitment?

The turbo downpipe connection changed during the 2015 model year. Early trucks use a V-band clamp. Late 2015 (2015.5) and 2016 trucks use a 3-bolt flange. Inspect your downpipe before ordering.

Do I need to delete the EGR if I only want the DPF pipe?

You can address each system on its own, but a partial setup without matching calibration can leave persistent fault codes or a derate. Review the full list of codes after a diesel delete and match the hardware to your tune before you buy.

Not sure which kit fits your truck? Check your year, cab, bed, and downpipe connection, then browse the 6.6L GM Duramax LML (2011 to 2016) collection and send us your truck details if you want fitment confirmed first. Free shipping applies within the continental U.S., and authorized returns are accepted within 45 days of receipt on items that qualify.