43 is kind of a catch-all code. If the O2 sensor, MAP sensor, TPS, or whatever is disconnected or totally screwed up, they have their own codes. But if they all together don't add up to an operating condition that makes sense to the ECU, it throws code 43.
Say for example your fuel pressure is wrong. The ECU would have to increase or decrease injector duration in order to keep your O2 sensor happy. Then it would throw code 43 because the ECU really has no way of knowing what your fuel pressure is. So there's lots of troubleshooting for this code, it can be many things.