The P0139 diagnostic trouble code (DTC) is an OBD-II code stored by your vehicle's Engine Control Unit (ECU) when it detects o2 sensor slow response (bank 1 sensor 2). This code is part of the Oxygen Sensors system. When your check engine light comes on and a scan tool reads P0139, it means your vehicle needs attention in this area.
OBD-II codes starting with P0 are generic powertrain codes defined by the SAE standard, meaning P0139 has the same basic definition regardless of vehicle make or model. However, the specific causes and repair procedures can vary between manufacturers.
Code P0139 is typically not an urgent issue and you can usually continue driving normally in the short term. However, you should still have it diagnosed and repaired to pass emissions testing and prevent potential complications down the line.