I have an 01 civic ex 5-speed. It's got the stock D17A2. The CEL recently came on the other week and the codes were a P0420 and P1457. Now the car won't go above 4,000 RPM in any gear and won't even rev past 4k either. Does anyone know what the problem might be. And also if you disconnect the battery terminal for a few minutes and clear the codes it will run fine and go above 4k til the cel will come back on and it will do the same thing.

 

Clogged cat. or an exhaust leak. The 4,000 RPM cutoff is called "Limp Mode".