Table of Contents

The LML Emissions System

The LML was the first Duramax to combine a diesel particulate filter with selective catalytic reduction and DEF. A stock exhaust runs these parts in order:

  • DOC (diesel oxidation catalyst): oxidizes hydrocarbons and helps bring exhaust temperature up during regeneration.
  • DPF (diesel particulate filter): traps soot, which is burned off during regeneration.
  • SCR (selective catalytic reduction): injects DEF to convert NOx. Monitored by NOx sensors upstream and downstream.
  • EGR (exhaust gas recirculation): routes cooled exhaust back into the intake.

How the LML Regenerates

The LML uses a hydrocarbon injector, often called the 9th injector, mounted in the turbo downpipe ahead of the DOC. During an active regeneration, the ECM commands that injector to spray diesel directly into the exhaust stream. The fuel reacts with the DOC to raise exhaust temperature and burn off the soot in the DPF.

This is not in-cylinder post-injection. Older Duramax engines (2007.5 to 2010 LMM) raised exhaust temperature by injecting fuel late in the combustion cycle, which could wash past the rings and dilute the engine oil. The LML's downpipe injector keeps that fuel out of the cylinders. If you are looking for an oil dilution fix, the LML does not have that problem in the first place.

If Your Truck Keeps Throwing DPF Codes, Diagnose First

Persistent DPF codes on an LML often trace back to the parts that support regeneration, not the filter itself. GM published a service bulletin (MC-10112228-9999) covering P0420, P24A0, and P2463 on 2011 to 2015 Silverado and Sierra 6.6L trucks and 2010 to 2015 Express and Savana vans with the LML and LGH engines. It directs technicians through the diagnostics and, where the results point there, to the Q57 indirect exhaust aftertreatment fuel injector.

Two things to have checked before you buy any parts:

  • Coolant temperature. Regeneration depends on the engine reaching operating temperature. A thermostat that sticks partly open can keep the engine cool enough that the ECM never runs a full regeneration, and the dash gauge often does not show it. Have a shop read the actual coolant and oil temperature with a scan tool.
  • The 9th injector. It lives in the exhaust stream, and the nozzle can coke up with carbon. A fouled injector cannot atomize fuel well enough for the DOC to build the heat regeneration needs. GM's bulletin path covers this part.

A diesel shop with GM diagnostics can check both. Fixing a thermostat or a fouled injector is far cheaper than replacing hardware, and it resolves the code for a lot of trucks.

Code Description
P0420 Catalyst system efficiency below threshold
P2463 Diesel particulate filter restriction, soot accumulation
P24A0 Closed loop DPF regeneration control at limit, temperature too low

Fitment: The 2015.5 Split

Check your truck's build date before you order anything.

The LML exhaust changed partway through the 2016 model year. Two different turbo downpipes were used:

  • 2011 to 2015: downpipe attaches at the turbo with a V-band clamp.
  • 2015.5 to 2016: downpipe attaches with a three-bolt flange.

Some 2015 trucks sit on the line, so look at your downpipe instead of relying on the model year alone. EngineGo lists separate LML kits for 2011 to 2015 and 2015.5 to 2016 for this reason. Order the wrong one and the pipe will not bolt to your turbo.

Important: Confirm your build date, cab configuration, and bed length before ordering. Message us with your VIN if you are not sure which side of the split your truck falls on.

What a DPF Delete Setup Needs

A DPF delete is not one part. The pipe, the 9th injector fix, the DEF side, and the tune all have to match.

Delete pipe

The pipe replaces the DOC and DPF section of the exhaust.

  • 4-inch: the common choice for daily-driven trucks with mild tuning. Quieter, and easier to fit.
  • 5-inch: for higher-power and heavy-tow builds where flow matters most.

See the LML Duramax delete pipe options to match a diameter to your build.

The 9th injector has to be dealt with

This is the step that separates a clean install from a dangerous one. When the DOC and DPF assembly comes out, the fuel line that fed the downpipe injector is left open. It is fed from the high-pressure fuel system, so if it is not capped or removed properly, it will discharge diesel into the engine bay.

Cap or remove that line according to the kit instructions before you start the engine. Then run the engine and check the fitting with a light for any sign of a leak.

DEF and SCR delete: the tune has to match

The LML injects DEF ahead of the SCR catalyst and watches the result with NOx sensors on both sides. If the DEF and SCR hardware is removed or disabled without a matching calibration, the ECM keeps setting DEF and NOx sensor faults and can derate the truck. The hardware and the tune are a matched pair, so buy them together and confirm the tune covers your model year. See the DEF delete kit options for your truck. Like the DPF work, DEF and SCR delete parts are intended only for off-road, race, or non-public-road use where permitted.

Tuning

The ECM has to be recalibrated so it does not command regenerations for hardware that is no longer there. Hardware without a matching tune will set codes and can put the truck into reduced power.

Choose a LML Duramax tuner that lists your model year, and confirm the 2015.5 to 2016 split is covered if that is your truck.

If you want everything in one order, an all-in-one LML Duramax delete kit bundles the pipe, the supporting hardware, and tuning support for these trucks.

Before You Add Power: The CP4.2 Question

The LML uses a Bosch CP4.2 high-pressure fuel pump with no factory lift pump, and it relies on the fuel itself for lubrication. A pump failure can send metal through the rails, lines, and injectors, and that risk exists whether or not you touch the emissions hardware. Read the CP4.2 fuel pump breakdown before you raise power, and talk to a diesel shop about a lift pump or CP3 conversion.

Installation Difficulty

A delete pipe swap is a job for someone comfortable working under a truck on jack stands or a lift. Plan for a full day.

  • Let the exhaust cool completely before you start.
  • Use rated jack stands or a lift. Never work under a truck held up by a jack.
  • Wear eye protection and gloves.
  • Have a second person for lifting the factory DOC and DPF assembly out. It is heavy and awkward.
  • Check each product page for the tools and parts your specific kit requires.

If you are not confident about the fuel line work on the 9th injector, have a shop do that part.

LML Delete Tuner Options: EFILive vs EZ LYNK

If you are shopping for an LML tuner with delete support, ask us which tuners we currently stock and support for the LML, and confirm coverage for your exact model year. Two names come up most often on this platform:

  • EFILive has long been the deep-control option for the LML ECM and TCM, and it is what many diesel shops use.
  • EZ LYNK is the handheld, cloud-based option. It is easier to use, and it works through an app rather than a laptop.

Two things to know before you pick a platform:

  1. US availability differs by platform and changes over time. Some tuning software has removed or restricted emissions-related parameters for US customers. What is available today may not be what was available a few years ago. Ask us what we can supply for your truck right now rather than relying on older forum posts.
  2. A cloud tuner leaves a record. Tuning that runs through an app and an online account creates a trail connecting your device and your truck. That is worth understanding before you choose a platform.

Do not assume any tuner will do the job just because it worked on an older Duramax.

FAQs

Is an LML DPF delete legal?

Not for on-road use. Removing or disabling emissions equipment on a vehicle used on public roads violates the federal Clean Air Act and many state laws. An off-road use disclaimer does not change how an EPA-certified vehicle is treated under federal law, and federal civil enforcement applies. Check federal, state, and local rules for your situation before buying or installing anything.

Do I need a tuner with my LML DPF delete?

Yes. The ECM has to be recalibrated so it does not command regenerations or flag hardware that is no longer installed. Running the hardware without a matching tune sets codes and can trigger reduced power.

Which pipe fits my truck?

It depends on your build date. 2011 to 2015 trucks use a V-band clamp at the turbo downpipe. 2015.5 to 2016 trucks use a three-bolt flange. Check your build date and order the matching kit.

Does a DPF delete fix oil dilution on an LML?

It is not the same issue it was on the LMM. The LML sprays regeneration fuel into the exhaust through the 9th injector rather than into the cylinders, so it does not dilute the oil the way in-cylinder post-injection did. If your oil level is rising, have the fuel system checked.

Should I delete the EGR too?

Many owners pair the DPF and DEF work with an EGR delete. See the LML EGR delete kit for the matching components. The same legal limits apply.

How much does an LML delete add in power?

Power depends on the tune, the fuel system, and the supporting parts, and we do not publish gains we cannot back up with a dyno sheet from your setup. Talk to us about what the tune you are considering is rated for.

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 VIN, build date, cab configuration, and bed length, and we will confirm which LML kit fits your truck before you order. Then check fitment and shop the LML Duramax delete kit collection.