Oxygen sensor

Hi everyone, I'm new here. I have a 2000 Hyundai Accent, supposedly a 1.5L.
A few days ago, I had to replace the exhaust manifold, but the mechanic couldn't find one for the same engine. He only found one without a catalytic converter and installed that one. However, it's throwing error codes for the oxygen sensors, and the car won't go above 3000 RPM because it feels like the engine is stalling and choking. The strange thing is that the oxygen sensors are supposed to have a 12-volt power supply, but when I measure the voltage, it's showing a super high 22 volts (it wasn't like that before). I don't know if it's damaged the computer. I was wondering if anyone could get me the workshop manual for a 2000 Hyundai Accent. Thanks in advance.

Hi, the lambda sensor has 4 wires: 2 white, 1 black, and 1 gray. The sensor isn't powered by electricity; it's a current generator that operates based on the oxygen level in the exhaust pipe. However, it does have a 12V power supply for the heating element connected to the two white wires, as the other two are signal wires. It's possible they're connected incorrectly, and the sensor failure could be due to a faulty catalytic converter, but it won't limit your power. In my opinion, the sensor isn't connected correctly. The ECU prioritizes the first sensor; the one after the catalytic converter is used to check if the catalytic converter itself is working properly. Also, when measuring voltage with a multimeter, test it on the battery's negative terminal, not on the sensor's wires. Regards.