L5P Custom Standalone Harness/Solution


DmaxSwap.com has worked to develop the cleanest solution for wiring your L5P Duramax drivetrain for simple operation with nothing more than power, ground, ignition and cranking signals. Our system includes a brand new OEM GM harness that has been modified by Standalone Harness to our specs and fully reloomed to OEM specifications. It also comes with a New ECM with custom calibration.

For TCM tuning we can unlock your T87 TCM and load a custom calibration or you can purchase a TCM from us with custom calibrations.

*Send in your good donor ECM and ECM/TCM harness for a $750 core credit.

** We do not offer this harness without ECM tuning as every setup is tested before it gets sent to you and requires our proprietary solutions.

***This custom standalone solution eliminates the Emissions controls for the L5P engine and is only meant for use on non-emissions controlled applications. It is the responsibility of the end user to adhere to local and federal regulations .



The Dmax Swap L5P standalone solution provides a simple and clean package to run the L5P Duramax engine and Allison 6 speed transmission (2017-2019) completely standalone in any application.  There is no Theft deterrent module, Body Control module or any other special modules required to make it run.  This system allows you to run the Engine and Transmission using the OEM control modules and sensors. Our custom ECM and TCM calibrations not only allow for standalone operation but also increased power up to 100hp over OEM calibrations and even more with further engine, turbo and fuel system upgrades. We can custom tune the engine and transmission for your unique build.

Important info about our harnesses…

Lead time on harness conversion is generally 4-5 weeks from the time it is received and checked in. At the time of check-in, the harness will be inspected and subject to additional charges (either mandatory or suggested) if there are any issues with wires, corrosion, pins or connectors.

We do not support Duramax integration into late model vehicles. This includes any integration with any factory gauges, factory body harnesses, etc. It doesn’t mean it can’t be done, just that we don’t support it. You will not retain control of the AC, tow haul or any other factory features that are controlled through the BCM.

Your harness is set up for standalone use only which in basic terms means the engine will run and the transmission will function. Due to the complexity of modern vehicles and their control systems, donor vehicle functions, conveniences or “nice to haves” are not offered or supported in any way as follows:

Tow-Haul Mode, Tap Shift, Electric Transfer Case Shifting, Axle Engagement, Duramax Idle Up, Fled Fuel, Starter Solenoid Control, Park-Neutral Starter Interrupt, Shift Interlock, AC Compressor Clutch Control, AC Req Idle-Up, AC Req Fan Control, Cruise Control, Vehicle Lighting, Donor Vehicle Gauge Clusters or any other donor vehicle features/conveniences.

You will be responsible for wiring your owner starter circuit with neutral safety and your own AC circuit if you are wanting AC. You can still leverage any of the factory AC components you’d like but it will be controlled separate from the harness. We recommend aftermarket HVAC, controls and dryer at least.

Gauges: We offer a 10% discount on any available Dakota Digital products with the purchase of our harness (contact us with specific product requests). The harness will retain the OBD port, so you can use that for your gauges or use some of the harness pigtails and add an oil pressure and coolant temp sensor to wire them directly. We recommend the latter if you’re planning to use the OBD continually for anything else because the signal isn’t always strong enough on an OBD splitter to run two devices. The CTS3 monitor can be used as a gauge cluster as well.

If you are interested in our standalone harness you can follow our ordering guide, purchase your harness modification a well as the ECM and TCM tunes and we can certainly get it running and driving properly for you.


Any attempts to make the above mentioned systems or features function are completely up to the customer and/or the installer.

Modifications will void any warranty or support, so it is crucial that you test start your setup with the harness prior to making any modifications. If you have not made modifications to the standalone harness, have proper tuning and are having issues with your test start, please see our diagnostics form.

Tuning Policy

Additional information

Weight 15 lbs
Dimensions 20 × 16 × 14 in
Harness Conversion

You will ship your donor, We supply donor

ECM Tune

You will ship your donor, We supply donor

TCM Unlock and Tuning

Send us your TCM, New TCM, No tune


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