All,

The CEL set on my Max two weekends ago showing DTC 0210 (P0174).  This
indicates that the system detected the left bank was running lean.

Possible faults:
1. MAF
2. Injector(s)
3. Air Intake leak
4. Bad O2 sensor
5. Exhaust leak

My diagnosis:
1. MAF
-> Nope - would likely affect both banks - car runs and pulls fine.

2. Injector(s)
-> Nope - listened to each injector (left bank is the front 3
cylinders on the VQ30DE) - each clicks normally and at the same
frequency.  Also, I didn't get any misfire code or feel any
hestitation when driving - so I'm pretty sure it's not one or more
injectors...

3. Air Intake leak
-> Nope: I had the top of the engine off two years ago when replacing
the valve cover spark plug seals and I replaced the upper-intake-
manifold gasket as well as all other intake assembly gaskets.  Also
I'd expect this to affect both banks.

4. Bad O2 sensor
-> Most likely.  O2 sensors are 60k old - mileage has been down about
10% over the past few months (before CEL tripped)

5. Exhaust leak
-> Nope: Didn't feel anything upstream of the O2 - no noise.

So before I order myself a new O2 sensor to swap in -> anyone else
have any thoughts or comments on my reasoning, or experience with this
fault?  I'm too lazy to swap the two front O2 sensors around to see if
I can move the fault to the other bank :)

I know on the 5th Gens, system lean codes for both banks would show up
at the same time, and that was usually the MAF...

Note: Resetting the ECU (to clear CEL) keeps it off for sometimes a
few days, sometimes a few hours.

Thanks,
Nirav