Ok, I really need some good advice and guidance here... I have an 02 Disco SD which recently was acting funny (rough idle, running in open loop, bad milage). I diagnosed it to the O2 sensors and changed them.

Only to see the reading on the UG show zeros afterwards. I assumed that it was wiring OR bad sensors. Most likely bad wiring, as all 4 sensors would not likely be bad. I swapped the front 2 sensors... still no change.

Frustrated I took it to the local LR mechanic, but they were not able to diagnose it, saying it is wiring and I need a new harness (most likely). I picked up the truck yesterday... the UG is now reading good on the Passenger side sensor AND the Driver side sensor is steady .445 (which I am guessing means it is bad, as it does not fluctuate) Both Rear sensors are showing .8 Also I am getting P-Codes of 0134, 0135.

When I was having issues and doing diagnosis, I had disconnected the sensors and ran the truck, the reading was steady .445... so I am assuming that the driver side is showing no connection.

The one worry I really have is - could it be the ECU? OR is it likely a bad batch of sensors and maybe wiring too? I know there is a lot of experience here and hope that maybe some guidance or advice would be available.

Thanks for helping

 

I would check for voltage on the heater circuit first. If there's no voltage there, the sensors won't get hot enough to work properly. The heater circuit wires are the ones that are the same color.
It's really hard to figure these things out without looking at the truck in person.

 

Ok, once I get off work today... I'll go see if I have the voltage. The heater cct wires are the same color you say? So at the each sensor is where you are referring? I have the RAVE manual and will try to follow the schematic. Just wondering where you would suggest checking for the voltage.

Thank you very much.

 

The heater wires are always the two that are the same color. Usually they're either black or white. The other two are a ground and a signal wire for the rich/lean reading. You can also back probe the signal wire while running the engine and it should have a wandering voltage from 0-1 volt if it's working. If the sensor is really stuck, shorted or open it will read a steady voltage. If it seems like it's working, but you're still not getting an accurate reading on the scan data, you can back probe the signal wire and touch one finger to battery positive and one finger to the probe and the voltage should max out on the scan data. It will go over one volt, then you know that the signal circuit is good all the way to the computer.

 

disc oh no, thank you for the help... I grabbed my tester and dug in this morning. Low and behold, guess what - the voltage pin from B1 S1 at the sensor was gone. So I think that is where I will start . A little frustrated, I took it to the mechanic and he told me to swap out the engine control harness - at least he didn't charge me anything. I am certain he didn't notice the missing pin, either way this should start me off and get things working again

Appreciate the helpful information and fault finding assistance. Cheers!

 

That's awesome! One pin will be WAY cheaper than replacing the entire harness.
Good luck! It sounds like you're well on your way!