Nissan Repair: O2 Sensor Problem Pathfinder 2001, oxygen sensors, volt ohm meter

Question
I have a Nisssan Pathfinder 2001 about a 8 months ago i install the 4 O2 sensor(original part) & now have the check engine light on again.Put a scanner it reads 3 codes:

P0130 O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
P0140 O2 Sensor CKT No Activity (Bank 1 Sensor 2)
P0145 O2 Sensor CKT Slow Respond (Bank 1 Sensor 3)

What does CKT means & where the sensor 1,2,3 located at?
This is not normal that in less than a year the O2 Sensor that were install has to be install again? Thank you


Answer
Eduardo,

YOu could have purchased defective oxygen sensors.  I have found a few of the Bosch ones to be defective shortly after installation.  Second, you could have an over rich condition that has coated the sensors with soot and they no longer respond properly.  The CKT means circuit.  Well, that is what I think it means.  My scanners do the same thing in the readout.  Sometimes it says circuit and other times it shows CKT.  Anyway, if it were me I would pull the one that says manfunction and get a digital volt ohm meter and check it against the book reading.  Get a Haynes Manual or a factory service manual and see what you have.  Email me back if you need more.