GMC OXYGEN SENSOR

I Have A Problem Code P0420 Bank 1 Sensor 2 Whitch O2 Sensor Do I Need To Replace?

I've Changed The O2 Sensor Like 5 Times And The Same One Keeps Going Bad And When It Gose Bad It Missfires And Runs To Lean And Low Volteg...

Po171 And Po174 Codes. 1998 Gmc Envoy 4.3 Liter Tuneup And O2 Sensors Have All Just Been Replaced

I Have A 1990 Gmc S15 Pickup And It Seems To Be In Very Good Condition. I Recently Had The O2 Censor Replaced Because I Had A Check Ingine...

I Need To Know What Pins On The Connectors And The Pins On The Ecm. I Need To Check And Test For Wiring Problems With The Upstream O2...

Any Reason You Can Elaborate On Why All These Codes Have All Popped In Together? P013a P013c P013e P014a P0158 P2273 P0138 P2271...