New to forum and want to thank all who participate. Having some confusion on locating o2 sensor for trouble code p0031 on 2000 mpv. From past posts it seems that the sensor i am supposed to replace is on the manifold. But it is only a 2 wire sensor. There is a sensor just before and just after the cat on the exaust pipe both of these have 4 wire. Is it the two wire sensor in the manifold or the 4 wire just before the cat on the pipe. Or neither? thanks for your help![:-]

 

The O2 sensor heater in the Right side exhaust manifold is the one that would set a P0031 code. The right side manifold is the one towards the rear of vehicle and not the one up front by the radiator. How many wires are coming out of the O2 sensor in the left side manifold by the radiator? Should be 4. There should also be 4 in the other sensor as well. I think perhaps someone has spliced in a very cheap universal O2 sensor that does not even have a heater and that is why you are getting the code that you are. If you will follow the wires from the sensor to the engine wire harness you will probably find that they are spliced into two wires that are Light green with red stripe and Brown with yellow stripe. Look around in that area for two other wires probably not connected to anything. One of them should be Yellow and the other Black with White stripe. These are the two wires that should be connected to the heater circuit of a 4 wire sensor.
The Sensor further down the exhaust pipe but before the converter is called the middle O2 sensor and would set an entirely different code.

 

Thanks!! After I removed it I found the other two wires!! It had 4 all along thnks for your help!! Code is off!!