Flash-Based Factory PCMs - Tech - In A Flash

Exposed: Flash-Based Factory PCMs

Brian Reese Apr 1, 2007 0 Comment(s)

In 1984, while we all marveled at the news of General Motors' stunning new Tuned Port Injection debuting on '85 Vettes, a far more important automotive technological breakthrough was taking place at Toshiba. Okay, so it wasn't exclusively or intentionally an 'automotive' technology, but the 1984 invention of 'Flash Memory' by Toshiba's Dr. Fujio Masuoka made more of an automotive impact than we'd have ever expected. Besides becoming the memory of choice for digital cameras, USB thumb drives, and computer BIOS, flash memory also became the first choice for automotive control computers. Before flash arrived, automotive computers relied primarily on erasable programmable read-only memory microchips, aka EPROMs or just 'chips' for short. EPROMs generally worked fine as memory devices, but ultimately reached demise from two key disadvantages: high cost and poor serviceability. The cost of the quartz-laden chip itself was expensive, and making it easily removable for service made the computer more expensive as well. Reprogramming an EPROM is a laboratory-like process involving chip removal, UV-light erasure, and chip 'burning.' In other words, dealership reprogramming was out of the question; service or updated programming meant chip replacement. When the flash memory technology reached commercialization, it was a sure bet to replace the EPROM. Flash-based memory was comparatively inexpensive, and reprogramming was a rudimentary process that could now be done through the assembly line diagnostic link (ALDL) connector.

Ten years after Masuoka invented flash memory it arrived in the all-new, on-board diagnostic (OBD-I) 1994 LT1 F-body powertrain control module (PCM). The spiffy new controller featured 128 kilobytes of flash memory and two 16-bit Motorola 6800 series processors. It actually used two separate computer boards, each with its own processor and flash memory, which many thought were independent for engine and transmission control, but GM referred to them as the Event and Time processors. The controller would remain unchanged through 1995 and was recognized with the service code 16188051. The '94-'95 LT1 Corvettes used essentially the same PCM, but with one additional microchip to begin OBD-II-like communications. The Vette controller used service code 16181333.

In 1996, the mandated arrival of second-generation on-board diagnostics (OBD-II) was the notable news. The LT1 PCM for '96 was similar in architecture to its predecessor, but featured a faster 6800 series processor and a doubling of one memory chip's size-for a total combined flash memory of 192 kilobytes. The service code for '96 was 16214399. The 1997 module was practically a carryover and is interchangeable with 1996 modules, but it hailed under a new service code of 16242921. The 1996 LT4 Corvettes also featured a relaxed knock module, which enabled more aggressive spark advance. Thanks to its plug-and-play interchange-ability, this removable knock module, identified by GM Part Number 16214681, became a transplant favorite for LT1-based '96 and '97 cars. Besides the knock module difference, the difference between LT1 and LT4 controllers was limited to the calibration.




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