Obd 2 code PO133 Hyundai Accent?

P0133 is a trouble code for o2 sensor, what it means is 02 sensor slow response bank1, sensor 1 (before cat) should be located before the flex pipe. What causes this code is that there are many reasons, one could be a faulty sensor, a bad exhaust leak or minor usually happens if the leak is before the sensor depending on which leak is greater. vacuum leak can cause this code due to not enough oxygen entering the exhaust manifold. check with the dealer or local garage, it is very hard to actually state which problem is causing this code.

Mine was coming on due to a massive exhaust leak, when fixed the code disappeared.