This Guy Released a Diagnostic Interface for a Jaguar Almost Nobody Owns

Getting full diagnostics from a modern car is pretty easy — if you’re a dealership or shop willing to shell out the cash for the manufacturer-approved equipment. Getting those same diagnostics from an older car is tricky, because the equipment is often out of production and hard to find. Getting those diagnostics from an incredibly rare Jaguar XJ220 is nearly impossible. At least it was before Tom Radom released Port220.

The Jaguar XJ220 is a supercar produced from 1992 to 1994 and in that time, only 282 were made. Because they’re so rare, getting your hands on one takes a lot of money. Prices are currently well north of $500,000 and that is just the beginning of the costs. Keeping that sweet Jag in tip-top shape is going to require a skilled mechanic with the right parts and tools — tools that haven’t been made in three decades.

The diagnostic tool to speak to the car’s Zytek ZM2 ECU, in partiscular, is so hard to find that it borders on legend. It doesn’t appear that the Zytek ZM2 was used in any other production vehicles and so only a few diagnostic tools were made. Those tools are, essentially, proprietary serial interfaces providing a connection to specialty DOS-based software.

Running that software actually isn’t hard at all. You can pop it into an emulator on a modern computer. But without the serial interface, it is useless.

Radom was able to get his hands on an original interface (the SPD-1039) and a laptop from the period running that DOS software. He intended to reverse-engineer the interface, so other XJ220 owners would be able to connect to their ECUs. But that wasn’t easy. The SPD-1039 was factory potted, so the components weren’t accessible.

However, Radom was able to connect a logic analyzer and a DB9 bridge to the SPD-1039 to look at traffic in PulseView. That helped him uncover quirks of the interface, including a very unusual 10,473 baud rate and some kind of inversion. Combined with reverse-engineering work done by Colin Bourassa on the DOS software, such as uncovering the commands for requesting data and writing to memory, Radom deciphered the whole interface.

From there, he developed his own hardware to replace the SPD-1039. The most recent version uses an FT232RNL bridge and gets its power entirely from USB, and is quite straightforward. It even supports Android connections.

Now anyone can build a Port220 service module with the open source files released by Radom. With that and the instructions on the Port220 website, Jaguar XJ220 owners can finally maintain their cars again.