PO136 and PO141 Codes on 1999 Subaru Forester: O2 Sensor or Wiring Issue?

Model: 1999 Subaru Forester Fault Code: P0136 Posted: 2010-09-15 12:03

I own a 1999 Subaru Forester with a 2.5L engine. About a year ago, before my vehicle inspection, I received a check engine light triggered by code PO136. I replaced the oxygen (O2) sensor in the exhaust system, and the issue disappeared temporarily. However, during the winter months, the check engine light returned. Upon diagnosis, two codes appeared: PO141 and PO136. After inspecting the wiring harness, I found that two wires were disconnected, creating an open circuit. Reconnecting them resolved the PO140 code, but within minutes of clearing the fault, the PO136 code reappeared. My question is: Is there a simple way to determine whether the issue lies in the wiring or if the O2 sensor has failed prematurely—within less than one year of operation? Are there any other sensors I should check for this recurring problem?