Diagnostic trouble code P0141 in your 2000 Ford Windstar indicates that the PCM detects an abnormal reading from the heater in the downstream heated oxygen sensor for bank No. 1. It may be an internal malfunction in the sensor -- in which case you'd replace the HO2S -- or it may be a wiring problem. The code most likely is not caused by a malfunctioning catalytic converter.
Check the wiring harness for the sensor. Make sure the harness isn't lying against the exhaust pipe, melted and shorted. Also check to see if the harness has water in it. Unplug the connector and make sure the contacts are not corroded. Sometimes just unplugging the connector and plugging it back in is enough to give the connector a fresh bite and good contact. Clear the DTCs using a scan tool or by disconnecting the negative battery cable for at least five minutes to see if the code returns.
With the ignition key on but the engine off, you should have 12V on the red and yellow wire going to the HO2S. If 12V is not present, you might have a blown fuse in the power distribution box. The PDB is in the engine compartment, between the battery and the fender. The blue 15A fuse in slot No. 19 provides voltage to the HO2S, but it also serves several other components. If the fuse is blown, you'll have several DTCs present along with the P0141. If the voltage is less than 12V, check the Windstar's battery and start chasing a low-voltage problem. If you do need to change the HO2S, apply light coat of anti-seize compound to the threads -- don't get any on the tip -- and tighten it to 34 foot-pounds.
