My CEL popped back up this morning travelling at ~20 mph on my way into work going uphill. I haven't had an opportunity to pull the codes yet, but I'd assume its probably the P0420 again...

I had these codes popping up and replacing the O2 sensors fixed them. Same symptoms, highway drives used to trigger the CEL. I didn't actually replace the passenger sensor 1 since that one requires removal of the drive shaft. The sensors are relatively cheap. I'd start there.

Replacing one O2 at a time is not a good idea. Always replace in pairs.

I will add that replacing the driveshaft was the easy part when I did mine. But I only disconnected it at the transfer box. Next time I will 100% remove it, because even with it moved my big hands got REALLY torn up. Also I think next time I will try from the top. With teh engine beauty cover removed, you can easily get to the O2. I think with the right tools going out the top may work. I went from the top to thread my in by hand and connect it.

That doesn't make sense... the front driveshaft is on the driver's side (US).

I won't dispute that 02 sensors are relatively cheap and easy and should be replaced in pairs. But I'm trying to follow the data on this one before throwing parts at it. Data shows that the condition indicated by the code exists, and the sensor in question is active and working. Rather than indicating a relatively steady ~0.45V (ideal) or ~0.6V (observed Bank 2) indicating a stable post-cat mixture, the bank 1 post-cat sensor is clearly tracking what the upstream sensors are doing. As I understand it that is the criteria for P0420. From another post here: "For these faults to throw, it needs to see the downstream O2 reading switching faster than it should, with relation to the upstream."

I haven't had a chance to work on it any more, but I do have another trip Friday. Hoping a full data log from cold to highway will show when and how the condition observed above starts to occur (assuming it repeats). I did find out that the catalyst temp PIDs do not appear to be supported on the LR3 engine management.

jagmandan,

Do you happen to know what the readings need to be in order to determine you have failed O2 sensors? Is this something you can do with the iCarsoft LR2 tool or do you need a GAP tool (or similar)? My local LR rep recommended getting the O2 readings before immediately moving onto replacing the cat.

I'm not really an expert, just reading everything I can find. Agree with your mech, you want to see the same sensor data I posted data above to give you an idea of what's going on. I'm not familiar with iCarsoft, but you don't need GAP for this. OBDFusion + Veepeak as describe above will do it, as will any number of other tools that read the standard PIDs via OBD. The data will tell you if you have any 'hard fails' like a non-responsive sensor, although that would typically be detected by the computer and set its own codes. The soft fail (slow response, inaccurate response) are harder to see but may be evident.

This thread has a lot of good info/discussion: https://landroverforums.com/forum/lr...failure-80162/ Djkronik57, I just noticed this was your thread... so I take it after everything described there new sensors solved it for you?

The LR version of the iCarsoft will graph O2 sensor output - so assuming no response would be the indicator of a failed sensor, you'd visually see the flat line output. Not sure if that answers your question but there you have it.