P0141 is for the heater of the secondary O2 sensor. Did you change the one in front? The one you need to check is in the cat, under the car.

Unplug the sensor, check the wire from the sensor. 2 of the wires are the same color (black?). Measure resistance between them, it should be 10 to 40 ohms. If that measurement is OK, then post back & we start checking other stuff.