For 2003, the Gen III PCM for trucks was upgraded with an even faster version of the Motorola 68000 chip. The same upgrade was rolled out on the car side in 2004 Vette and GTO. The flash memory was now doubled from 512 kilobytes to 1024 kilobytes, to help facilitate further expansion of control coding. Externally, the new PCM was identifiable by its 'green' connector (replacing the 'blue' connector found on '99-'02 PCMs). This PCM would remain basically unchanged through its remaining usage up to 2007. However, several service codes existed due to internal manufacturing or sourcing changes, such as Intel-brand flash memory or AMD-brand flash memory. This brand-swapping was fairly transparent to the user, but caused tuning and diagnostic tools to be re-designed to ensure compatibility. The service codes for '03-'07 include 12576106, 12586243, 12586242, 12583560, 12583561, and 12589463. These PCMs are interchangeable, with a complete re-flash of the appropriate operating system. Thanks to its fast processor and large memory, this PCM is considered the optimal choice for LS1 transplants.
By 2008, federal law requires all factory controllers to be controller area network (CAN) based. GM got a jump on the new architecture with the Gen IV LS2 and truck LH6 engines in 2005. The totally new engine control module (ECM), dubbed E40, still used a processor from the Motorola 68000 series, but a newer and faster version. Flash memory size remained 1 megabyte, the same as existing LS1 PCMs, but it was a newer generation of flash. The increases in performance were complemented with a radical reduction in size as well. Following the nature of electronics evolution, the new box was drastically smaller than its predecessor, and also featured highly compacted, smaller connectors. The E40 also only controls the engine. Transmission control was separated out to a new stand-alone controller, the transmission control module (TCM), named T42. Yet both new units combined were still much smaller than one combination LS1 controller. The new TCM is also a flash-based unit, featuring 1 megabyte of memory. This separation of PCM to ECM and TCM allowed for easier powertrain integration between the various platforms utilizing Gen IV powertrains. The E40 would only serve two years as a GM controller between '05 and '06.
...The new box was significantly slimmed down from the original '97-'98 boxes. A new removable aluminum access panel also appeared starting in 1999. The same box served through '07, but received a major internal upgrade in 2003. The 2003 PCM is shown, identifiable by its 'green' connector. | 
The only consistent externally visible difference between '99-'02 and '03-'07 units is the color of the second connector. Older units sport a 'red' connector and newer units feature a 'green' connector. Both units also have one 'blue' connector. The PCM terminal connectors are labeled, as shown. |
The guts of the LS1 controller look fairly typical for a modern electronic part. The flash memory chip is labeled "A" and the processor is labeled "B" in the shown photo. | |