If You Do A Little More Research Youll Find That There Are Several Things That Can Trip An o2 Sensor Related CEL. IIRC The PO136 Is For A Heater Circuit Malfunction On The O2. You May Be On The Right Track Thinking About The Wiring. The Code Is Basically Telling You That The Catalysts Are Not Lighting Off At The Correct Or Optimum Temp. Somebody Yell If Im Incorrect!!! It Could Be Anything From The Wiring Having Moisture Built Up, To The Cat. Going Bad.
The Reason The CEL Came Back On Is That The Computer Will Try To Diagnose And Compensate For The Problem For Three Key Cycles. If The Problem Persists, Then The CEL Will Come Back On....So, Basically You Didnt Fix The Problem.
