The LR3 had been great, OTHER than 0171 and 0174 codes keep returning. Go away for a while then come back.

Replace Alternator and Battery
Replaced MAF
Smoke test
2 02 sensors

I cannot seem to figure this out!

Could it be a dirty throttle body and and injectors?

 

Which O2 sensors? Upstream? Not that they are probably the problem, both banks don't typically fail at the exact same time.

TB is easy to clean, so why not do it just to rule it out.

How old is the PCV valve?

Check all of your intake plastics. I found a pretty good crack in my MAF housing on the underside, downstream of sensor. And check all the vacuum pipes. Also take a look at the oil cap/extension tube. I have never owned a vehicle that can not operate propertly with the oil cap off, but the LR3 does not like any air leaks in the least.

 

If no vacuum leaks, replace PCV valve (with genuine) since you have already done MAF (also genuine I hope?) and clean TB

I had these codes which a manual TB cleaning (spray/wipe), new PCV valve, and ultimately new MAF cured

I have put on 25k miles since - no CEL

 

Now the boy says he is getting a p0420 code.

Why do we do this to ourselves.

 

How old are your spark plugs? Any misfires? How many miles?

I'd still clean the induction system, TB, PCV valve before worrying about cats

 

Actually, not sure how old the spark plugs are. I am not getting any codes related to misfires.

 

Check out this thread;

https://landroverforums.com/forum/lr...4-codes-86034/

Just got rid of the same codes by putting gasket maker on the throttle body metal gasket and the two metal gaskets around the EGR valve. I’ll bet that will fix your’s too.

 

^ Thats an interesting thread. I have two new genuine gaskets in hand. They appear to have a very thin coating. But I feel they are one-time use. Once disturbed, they should probably be replaced. At least by the book. I had lean codes after replacing my spark plugs that would not go away after cleaning. Took disconnecting the battery for them to go away. A short bit later, I replaced upstream O2 sensors. While I have a milage gain, its not as high as I feel it should be. I think I will use some high-temp Reinzol on all of those gaskets and see if things improve.

 

Also, don’t forget to reset the fuel trim adaptations. Some say removing the negative battery cable overnight works.

 

I have been doing A LOT of reading today. Normally I would agree that a battery disconnect would reset things. Now I am not so sure if that works for a full, proper adaptation reset on the engine computer.