[jwalker1970]

I just replaced a transmission on a 99 Explorer 4.0L (OHV vin X)

After about 100 miles of driving I got P0171 and P0174, indicating lean on bank 2.

I used my MT-2500 to read 02's and they read as follows as you throttle up & down:

02S11 & 02S21 (R side) fluxuate between about 200 and 800 (rich-lean OK)

02S12 & 02S22 (L side) are pegged at 0, no movement whatsoever.

I unplugged front 02 sensor on R side (bank 1) and it pegged to zero.
I unplugged rear 02 sensor on R side (bank 1) and it pegged to zero.

However, there is only one 02 sensor on bank 2. It stays at zero whether plugged in or not.

Normally I'd suspect a bad 02 (bank 2, sensor 1), but having both Left sensors read zero is throwing me for a loop.

Thanks in Advance!!