My "Check Engine" light came on today. The scanner at AutoZone reported one code.

P0141: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

Can anyone tell me which O2 sensor this is and where it's located?

Thanks in advance.

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1998 E320 120K mi
1991 Miata 80K mi
2001 Ranger 109K mi