I have a 95 VDP with a problem even my mechanic is stumped. There is no voltage on the downstream O2 sensor. Changing out the sensor and the normal switching returns. CEL is extinguished. After sitting overnight when retested there is no voltage again and the ECU doesn't see the sensor turning on the CEL. Otherwise the car runs fine, starts quickly, accelerates normally. It has 112K miles. I have changed both upstream sensors, fuel filter, and EGR valve. Mechanic found the downstream sensors cross connected and corrected that. CEL went out but returned in less than 15 miles. The rich condition uses more fuel, reducing my MPG from 18 in normal commuting to 15. Anyone seen an issue like this? Have you solved it successfully? Thanks...go Hawks...

 

Although I nver actually proved it myself, it used to be a common rumor for the X300 that cross connecting the sensors could lock up the control system in some way, requiring a "lambda re-orientation" by WDS or IDS software. When you say "no voltage", do you refer toi the heater or sensor circuit? How are you reading the voltage? In fact, if you disconnect a sensor, I believe the ECU input circuit on an X300 will read about 4.5 volts to
ground due to the way the sense circuit works for a titania lambda sensor as used on these cars.

It is really not very hard to find a loss of voltage if you know what you are looking for. If you are actually reading 0 volts to ground on the sense circuit with both a meter and with the OBD scanner, you almost certainly have a wire or sensor shorted to ground.

I would also have a look at the ecu connector pins for water and corrosion. It is in the RH front kickpanel.