is the o2 sensor (connector color) on the driver side blue or green? would it matter? SEL keeps coming on after the know it all tech's at the dealer messed with them. they put the blue on the driver side and green on the passenger side. i saw a pic with green on the driver side and blue on the passanger.

http://my350z.com/forum/exhaust-423/

 

i don't know which is which but i do know the connector on the harness side is the same as the component. that you can tell if they are swapped since they both have differant lengths.

and it could possibly be a ground issue not the sensors themselves or it could be a bad cat since the rear O2's primary function is montoring catalyst efficency.

 

i have crawford cats HFC, so how can i tell if a cat is bad? where would the ground be for the o2 sensors?

 

its switching frequency between sensor 1 and sensor 2 the only way to do it is have the proper tools i use consult II or consult III for this test. Your high flow cats are probably to blame in all honesty. I personally wouldn't have put those parts on a car if it had aftermarket cats. The grounds are behind the glove box and by the steering column on the dash tube since thats the main ground for the car. all black wires with a gold bolt.