How a Modder Discovered Secret 'Gran Turismo 4' Cheat Codes 18 Years After the Game Was Released

When a game is as as old as Gran Turismo 4 — which just celebrated its 18th birthday in February — you kind of assume everything there is to know about it has been unearthed already. That’s why the GT4 news that made the rounds on Twitter this past weekend came as such a surprise: A modder discovered cheat codes in the 2005 racing sim that nobody knew about before. Here’s how it happened, according to the individual who made it possible.

In case you missed it:

Before we get to that, some background on the cheats themselves. They’re fairly standard, but practically blow the game wide open. One gives you 10 million credits, while others let you earn “gold” on any license test or any race event automatically with a simple button sequence.

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The catch is that these codes only work after 365 in-game days have passed, which either requires hours of normal gameplay beforehand, or necessitates the player accelerate progression with tricks like buying aftermarket wheels or entering and exiting license tests.

The breakthrough happened today, rather than a decade ago, because it was only a few years back that a modder and data miner who goes by the name of Nenkai was able to parse out what’s been lurking within developer Polyphony Digital’s bespoke programming language. I spoke with Nenkai recently; here’s how the discovery came about, in his own words:

So GT4 (and all the games since then) runs a custom, compiled scripting language named Adhoc which needed to be fully reverse-engineered first to make any sense of what the game was doing. It sits on top of the PS2 code, to program the game more easily. So back in 2020, I figured it all out, and it kind of felt like opening pandora’s box, people including myself were disassembling the games and randomly looking at parts of it until some oddly specific numbers which happened to be button keycodes along with “command checks” were found, when piecing it all together debug menus were found, a special menu was also found for GT4.

And that was basically the end of it for a good while.

With myself making more tools for modding GT4 recently and TheAdmiester making use of them I thought I’d go on a project to reverse-engineer the entirety of the GT Mode script compiled code back into compilable source code to allow logic-based modding. With that going rather well I randomly noticed some more codes that I wasn’t aware of nor were documented anywhere, so I booted up [emulator] PCSX2 and attempted to activate one of them, and it didn’t work.

Nenkai then attempted to enable the codes with the use of a metaphorical second controller in the PCSX2 emulator, because that’s what GT4’s special menu requires. That didn’t work either, leading him to think they weren’t actually implemented. Until he noticed something:

The catch was a sneaky game day check. So I went ahead and edited my save with my save editor to advance days and tried again, and heard that noise. Later on I also tested with Tourist Trophy, which is almost just GT4 in disguise internally, and that worked as well.

Image: Sony Interactive Entertainment

That’s right: these cheats work in Polyphony’s motorcycle racer Tourist Trophy, too! If you’d like to try them yourself, here’s what you have to do, via The Cutting Room Floor. Again, 365 in-game days must have passed before they’ll work:

10,000,000 Credits (GT Mode Screen): Select, Left, Right, Right, Down, Up, Up, Left, Down, Up, Right, Left, Down, L1, R1, Select

Pass any license (License Selection Screen): Select, R1, Select, R1, Select, L2, L2, R2, R2, L1, Select, L1, Select

Gold any specific license test (License Test Selection Screen): Select, Select, R1, R2, L2, L2, Select, L1, R1, Select, R2, L1, Select

Gold any event (Event Course Selection Screen): Select, L1, Up, Up, Select, R1, Down, Down, Select, L2, Select, R2, Select

There is an extra code usable in the Mission Hall, which also adds 10,000,000 Credits. It is presumably implemented incorrectly and should instead allow completing any mission. The code is Select, R2, Select, R2, L1, L2, L2, Select, L1, R1, Select, R1, Select.

But why are they even in the game to begin with? We’ll never know without a confirmation from the devs, of course. As with many cheat codes, it’s possible they were originally used for internal testing. Perhaps they were placed behind a day check for the public release so that players wouldn’t be able to get everything right from the start.

Gran Turismo titles have never been known to have cheats — even back in the day when that sort of practice was more common — so you could imagine how valuable this knowledge would have been over at IGN or GameFAQs in 2005. Today, the impact is different, but at least you can save yourself a little bit of time during your next playthrough. No need to B-spec that pesky Nürburgring 24-hour race to nab the Formula Gran Turismo any longer.