Hey. My cousin just info me that he got engine check light now. I scanned it and it showed P0140. I not sure which one is bad 02 sensor before we can ahead buy one. Instead not buy all 4 which is waste money. The reason we not sure which one we need to know. He have a 2003 GMC truck 4 doors its 2500HD 6.0 v8 engine. We did replace the rear one 02 sensor since it was damage the wire by driveshaft. We put new one and zip all wires to avoid from anything hit to damage. About 3 weeks later now engine light back on. I check it show P0140. See if yall can help us out fast. Remember we have two cats not y pipe at all. It is all factory.

 

P0140 refers to Bank 1 sensor 2 Oxygen sensor showing insufficient activity. AKA "lazy". The biggest problem is usually the owner replacing the wrong sensor. Bank 1 refers to the side that contains cylinder #1 (left). Sensor 2 is the rearmost sensor AFTER the cat. Insufficient activity usually means, a bad sensor IF the wiring is okay.

 

Not make sense We put new 02 sensor on left side after cat. Wires connect good. So?

 

the sensor may have gone bad.Swap it with the other one after the cat

 

It is so impossbile. Cause we repalce TWICE with brand new for 3 weeks old. Bought from AutoZone