Wiring Diagram:

Fig 1: Wiring Diagram - DTC P1154 O2 Sensor Circuit Range/Performance (Low) (Bank 2 Sensor 1)

Courtesy of SUBARU OF AMERICA, INC.

DTC P1154 DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1. CHECK HARNESS BETWEEN ECM AND FRONT OXYGEN (A/F) SENSOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connectors from ECM and front oxygen (A/F) sensor connector. Measure the resistance of harness between ECM and front oxygen (A/F) sensor connector. Connector & terminal (B134) No. 27 - (E24) No. 1: (B134) 34 - (E24) No. 3:	Is the measured value less than 1 Ω?	Go to step 2.	Repair the harness and connector. NOTE: In this case, repair the following: Open circuit in harness between ECM and front oxygen (A/F) sensor connector Poor contact in front oxygen (A/F) sensor connector Poor contact in ECM connector
2. CHECK POOR CONTACT. Check poor contact in front oxygen (A/F) sensor connector.	Is there poor contact in front oxygen (A/F) sensor connector?	Repair the poor contact in front oxygen (A/F) sensor connector.	Replace the front oxygen (A/F) sensor. < Ref. to FRONT OXYGEN (A/F) SENSOR . >