They way they work is to react with oxygen. Post cat the oxygen supply is pretty stable and minimal from the canalization process. Frankly I never really worry about rear sensors unless a I have a code for a cat failing. At which point its either a bad cat or a bad sensor. If replacing the downstream sensor does not clear the code, time for a new cat. If you are getting a cat code and hav a sensor that is al over the place, including a new one, then it could be a bad cat of exhaust leak upstream which is pulling in excess air (excess oxygen).

 

Just went through a very similar experience. Had two dead Bosch O2’s right out of the boxes from Amazon. Ordered 2 Walker O2’s from Rock Auto and sent the Bosch ones back to Amazon. Night and day difference. Disco is running great now.

Here’s my post about my experience. Hope it helps!

https://landroverforums.com/forum/di...s-bosch-98410/

 

Not sure which system motronic has...

NOTE: On early OBD II systems, the post catalytic converter O2 sensor has no effect on fuel control. The post catalytic O2 sensor was originally responsible for only monitoring catalytic converter efficiency. On most systems, the post converter O2 sensor signal should never mimic or follow the pre-cat O2 signal. That would indicate a defective or low oxygen storage capability at the converter . On early OBD II systems, the post-cat O2 sensor should show little or no voltage fluctuations on a scope waveform, since all the mixture fluctuations are being absorbed by the catalytic converter.

Stating around model year 1999, a new type of converter came on the market, called “Low Oxygen Storage Converter” or LOC. With an LOC, the pre and post O2 sensors cycle at the same rate. These converters are tested by measuring the lag-time between the two signals. A further development of this system is that the post converter signal is also used for A/F correction, but to a less extent.

o2-sensor-testing

 

Weird that the downstream NTK's are half the cost of the upstream on Amaon

 

So i ordered walkers and rewired the connector, i cleared my heater code, however I’m. Still getting P0134. On live data I’m getting 0 volts on that sensor but my bank two sensor is working fine. Switch the sensors and same thing. I want to check the wiring to the ECU. How would i do that (what color wires and what readings should i be getting on a multimeter? ALSO i have a spare ECU (no BCU) and my local stealership will reprogram the VIN or so they say.. would that be an option?

 

Also i have bad valve cover gaskets and I think a Vacuum leak as well... would that trigger the o2 codes?

 

Any update on this?