I have a 2006 LR3 with ~180,000 miles that was presenting CEL. Vehicle experienced rough idle and intermittent stalling with A/C running while idling at intersections. I scanned with the iLand and identified the following codes:
P0101-00, Mass or volume air flow - circuit range/performance (Historic)
P0171-00, System too lean (bank 1) (Intermittent)
P0172-00, System too rich (bank 1) (Historic)
P0174-00, System too lean (bank 2) Intermittent)
P0175-00, System too rich (bank 2) (Historic)

I removed/cleaned/reinstalled the MAF sensor and throttle body. Rough idling cleared up and vehicle no longer stalls with A/C running. However, the following CEL codes reappeared:
P0171 and P0174, System too lean (bank 1 and bank 2) (intermittent)

I ran several different data streams with the engine warmed up and will attach all to this threat for reference, but noticed that the O2 sensors output voltage for Bank 1 - Sensor 2 was 0.07V and Bank 2 - Sensor 2 was 0.85V. The bank 1 sensor 2 voltage started close to 0.85V then abruptly dropped and remained at 0.07V. I ran a diagnostic test on the purge valve, EGR valve, MAF sensor voltage, bank 1 bank 2 fuel system status, etc, and will attach all the charts.

Is this an indication the O2 sensors are bad? Can bad O2 sensors cause lean conditions? Any input and further troubleshooting tips are greatly appreciated! Thanks in advance!
Nate

 

I may be mistaken but I believe oxygen sensor 2 refers to the downstream (after catalytic converter) O2 sensor and not the wideband upstream sensor that will drive fueling trim changes. Unless I'm wrong re: upstream / downstream, I would ignore the sensor 2 voltage data and just focus on starting with what the error codes are telling you: you have a lean condition affecting both banks. Yes, that could mean you have separate issues that together are causing both banks to run lean, but let's start with the simpler assumption: you have an air leak before the air splits into both banks. That mains you should examine every connection point from the MAF to the throttle body (you have the V8, correct?). Typical failure points in this span include:

1. the airbox resonator after the MAF is prone to cracking
2. make sure hose connectors are tight
3. gaskets on the smaller pipes can fail

The easiest way to check all of the above at the same time is to pull the airbox/MAF housing and run a smoke machine. The smoke will identify any cracks, and then you can fix those.

If the smoke test shows nothing, then you would check further downstream. A few weeks ago my search for a single-bank lean issue went unsolved until finally, after having worked downstream starting with the air resonator at the intake, I replaced the fuel injector seals.

Given the age of the truck and the miles, my bet is you have cracks in the air resonator. I have had very tiny cracks in the air resonator cause lean codes. If you do have cracks, you can seal them up with RTV for a temporary fix but replacement resonators are a better solution. Good luck with it. - scooter

 

Thanks Scooter for the response. For more context, I have the 4.4L V8. Within the last 2 years I've replaced the resonator as the old one was cracked, and replaced the MAF with the $170 part from AB. Neither fixed the lean condition. I read on another post that the metal EGR pipe can loosen over time. I'll check that. I usually run a can of BG Platinum 44K through the tank at every oil change so I doubt it's a fouled fuel line or injector. I've cleaned the oil fill cap gasket and replaced the dipstick gasket. We've had the truck since 2009 and haven't ever replaced the EGR or PCV valves.

I'll start with tightening the EGR pipe tonight and resetting adaptations. I'll double check the resonator for cracks and will follow up with findings!

 

PCV valve can fail, valve cover gaskets can leak, EVAP can leak without throwing code if small leak, etc. You need a smoke test if you want to really find it maybe. With that said, you can seal off almost every vacuum port less brake boost and see what happens too.

 

Buying a smoke machine! I'll circle back with results.

 

For the record I have had both banks lean for some time now. Runs great tho, no issues. I have new valve cover gasket's to install first. If that does not work, I move onto removing the entire intake and putting on all new gaskets. If that does not work I go back to ignoring the codes. LOL

 

No kidding! We've been ignoring this issue for a few years now...mostly. We've got an '04 Disco 2, '06 LR3, and '10 LR4. Mnx never ends! Luckily, we no longer live in NH, otherwise chasing endless CELs to pass annual emissions tests would bankrupt us...LOL

Today I cleared the adaptations, replaced o-rings on PCV valve and pipes, and verified no cracks on resonator. When I get the smoke machine, I'll run it and follow up. Thanks for all the input so far!

 

Nice fleet! Which one is your favorite?

 

All of them! Despite all the headaches, I can't imagine driving anything else.

 

“Favorite” implies singular. You must choose! 🤣