just finished swap into 91 std hatchback and ecu reads o2 check engine i replace the old one with a new aftermarket one could that be the problem

 

did you already replace it??

 

yea it's a bosh o2 sensor could that be the problem

 

In my experience, the ECU won't set a code for the O2 sensor too quickly. You could drive for months with a malfunctioning slow and lazy sensor and the ECU wouldn't care as long as it sees something. I would check the wiring connection(s). A hard failure like that will definately set a code.

BTW, I've had poor results using the Bosch generics. Just my experience though.

 

Make sure the wiring is right if it is a universal one.