Can I DIY a standalone harness from a Gen IV E38 ECU for an LH6 5.3 swap, and how do VATS delete and speedo calibration work?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

VATS / anti-theft

• P01, P59, E38, E67: In the factory architecture the theft decision lives outside the PCM: the IPC/BCM decoder interprets the R-Code and transmits the approval to the PCM, so a swap with no BCM must have the check disabled in the PCM itself. (Directed Electronics)
• Per HP Tuners, a VATS disable is required when swapping the powertrain/engine from one vehicle into another so it starts and runs properly; it is not required when tuning a stock GM vehicle. (HP Tuners)
• E67; LSA, LS9; 6L80E/6L90E; 2009-2015: PSI states that all of its standalone harnesses (e.g., HAR-1098 for 2009-2015 LSA/LS9 with 6L80E/6L90E and E67 ECM) require PCM VATS removal, which PSI offers. (PSI Conversion)
• E38, E67; LS2, LS3, LS7, LSA, LS9, L96, LH6; 2005-2017: E38/E67 ECMs do not have a simple global VATS disable like the LS1 PCM; per EFILive's developer, VATS must be disabled by patching the OS to force the VATS check to always pass. (EFILive)
• E38, E67; LS2, LS3, LS7, LSA, LS9, L96, LH6; 2005-2017: In EFI Live the E38/E67 VATS-disable parameters are: G1210 (select Anti Theft system Type 2 or Type 3), B9903 (Disable VATS Patch, applying the OS software update that disables VATS), and the tune must then be written with a Full Flash. (EFILive)
• E38, E67; LS2, LS3, LS7, LSA, LS9; 2005-2017: EFI Live parameter G1220 defines the starter relay type with options Apply to Ground, Apply to 12V, and Not Used; 'Not Used' is for engine conversions where the ECM does not control the starter relay and must not be set on a factory vehicle. (EFILive)
• E38, E67, P01, P59: In EFI Live, a full flash programs both the PCM's operating system and calibration, while a calibration-only write skips the OS; a VATS patch lives in the OS, so a calibration write alone will not apply it. (EFILive)
• E78; Gen V V8 (Ecotec3); 2014-2019: For E78-class controllers there is no calibration-level VATS parameter at all; VATS removal is done as an ECM OS patch only, followed by a full flash. (EFILive)

Harness and power

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• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: Harness uses GM Delphi connectors and cross-linked 600 V wire. (PSI Conversion)

Confirm against the instructions for your exact parts before wiring. More: VATS / anti-theft in our tuning guide.