P0420 code usually pops up when your car detects that the catalytic system isn’t working as efficiently as it should. It’s basically the ECU saying something like “eh, this exhaust flow not normal lah.” Most of the time, this happens when the catalytic converter is getting old, slightly clogged, or when the exhaust setup has been modified and the readings no longer match factory specs. Instead of replacing parts, one popular approach among enthusiasts is doing a catalytic system off (DeCat style setup) through ECU or system adjustment. In simple terms, the catalytic monitoring is disabled or tuned out, so the system stops triggering P0420 even when the exhaust setup has already been upgraded. The main reason people go for this is performance. When the exhaust system is less restricted, the engine can breathe better and push out gases more freely. This usually translates into better throttle response, smoother power…
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