Hi,
My 1999 ML320 displayed Check Engine Light, it went on and off a couple times. At the present time, the light has been off for more than a week. OBDII reader scanned code PO156 (bank2, sensor2) and pending code PO161 (bank 2, sensor2). Is the O2 sensor defective? Or might it be a wiring? The car has only 49k miles.

Thank you.