Wiring Diagram:

Fig 1: DTC P0139 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)-

Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC STEPS DTC P0139

Step	Check	Yes	No
1. CHECK ANY OTHER DTC ON DISPLAY.	Is any other DTC displayed?	Inspect the relevant DTC using "List of Diagnostic Trouble Code (DTC)". < Ref. to , LIST OF DIAGNOSTIC TROUBLE CODE (DTC) . > NOTE: In this case, it is not necessary to inspect DTC P0139.	Replace rear oxygen sensor. Ref. to FRONT OXYGEN SENSOR AND REAR OXYGEN SENSOR .