So this seems to be a common issue, 2004 discovery SE7. P0130 stored and P0150 Pending, CEL on, Gas mileage is horrendous. all 4 sensors replaced 2 years ago.

1. Cleaned MAF and checked with multimeter. Results: Functioning properly.
2. Smoke tested truck with tube and cheap cigar. and checked around for any hoses that were disconnected or broke. Results: No leaks or broken hoses that I see.
3. Dropped off at Pikes Peak Rover here in Colorado Springs and paid for and hour of diag. Results: codes cleared and confirmed the front 2 pre cat sensors were only code to return. nothing else showing problems. Told I had a really clean truck and that it was worth keeping on the road. Cool.
4. Checked harness with multimeter. Results: Both connectors showing .44 volts with ignition in the on position.
3. Pulled o2 and heated it with torch while connected to multimeter. Results: No voltage...dead.
4. Did search on Land rover enthusiast forums. Cleaned connectors with CRC contact cleaner, cleaned that harness plug by the fender. Results: no improvement.
5. Confirmed that sensors were replaced with OE MHK100930 and MHK100920. It appears they were and these are OE Bosch. Confirmed with land rover dealership in Denver that Bosch MHK100930 and MHK100920 is correct part for my truck.

Here is where im at. Im just going to replace the 2 fronts with new OE bosch MHK100930 and if they dont work or get killed ill return them. Doubt its the issue. I will also check the ECU or replace it as i see a 2004 discovery ECU is cheaper than an o2 sensor. After all my searching on forums I find that there are people with this problem who never post a resolution or update and thats frustrating. Iv read through a ton of posts about o2 related issues and nobody confirmed if the advice or fixes worked and thats what made me want to work through this on here. Am i missing something here? is my ECU idea going too far? Has anybody actually solved their o2 issues who could point me in the right direction?

 

I’ve been through this before. Walker sensors seem to be better. Also the connectors themselves can get contaminants in them. Make sure your spray them out with electrical cleaner and protectant before adding the new ones in. Then reset the Ecu and drive again.

 

I am having the same issue with my new to me 2004. I hate to throw parts at it, so time to test the sensors I guess. Who has the best prices on the Walker ones?

Codes I am getting are:
P0154 Oxygen Circuit No Activity Detected (Bank 2 Sensor 1)
P0134 Oxygen Circuit No Activity Detected (Bank 1 Sensor 1)
P0135 Oxygen Sensor Heater Bank 1 Senso 1
P0155 Oxygen Sensor Heater Circuit Bank 2 Sensor1

And I think a previous owner or car dealership or someone has been into the cluster as even with all of these codes my CEL isn't on. Possibly a removed bulb?

 

It's easiest if you have a known good sensor you can work with. You need a tool that can chart analog sensor voltages real time. Start with the engine cold and watch the voltages. Cold it should start off at least .5 volts, maybe higher. If they trend down after that and bottom out the problem is not the sensors, the engine is actually lean. If you really want to test you can open a propane torch without lighting it and put it near one of the vacuum lines, pull the line off and let the vacuum suck in the propane. Voltage should go up over 1 with that test. You are purposefully feeding it too much fuel.

 

BTW, I did have a bad ECU once where the oxygen sensor drivers quit working. Confirmed with space ECU. Good idea to have a spare around. You can buy a good spare used set off ebay and re-sell it later if you don't need it.

 

Bench test the replacement sensors you get before installing them to confirm they are working (with a torch and a multimeter). I, and others, have had Bosch sensors that are bad out of the box, although the probability seems low that you would've had two of them bad out of the box at the same time.

 

one thing to check if your rig is running rough etc and throwing codes is to check your fuel purge valve, if its sticking open its letting in air throwing everything out of wack, i had this issue

 

I actually had these same codes thrown as well as a page of others. My local indie cleared my codes and everything went away and hasn't returned but the 2 I have now. When I went to pick my disco up the light was off and then came back on not even minutes after I left the parking lot. There's definitely an issue with intermittent codes on these things. That was actually a major relief.

 

You don't really need to do all that stuff. Look at the STFT and LTFTs on a scanner. Look at the oxy sensor voltage on a scanner. Look at whether the ECU switches to closed loop with a scanner. Both front sensors could die at the same time, but it is unlikely. The ecu will also fault the oxygen sensors if the engine has a big vacuum leak. It will add up to 25% fuel at idle, if it doesn't see the oxygen sensor voltage change it will decide that the sensors must be faulty, when in reality a vacuum leak has stopped the ECU from being able to fuel it into stoich. Also check with and without the MAF plugged in. Without the MAF plugged in the ECU it will run Alpha-n with the factory map and trim with the 02s. So if it runs and trims in closed loop with less than 7% with the MAF unplugged, the MAF is bad. Poking around with a multimeter won't do much good.

 

@RoverMasterTech I check my LTFT and STFT, regularly can you provide some direction on what a good range is for both ? The suggestion to check is given all the time but no guide lines of what is "normal"