Nissan Repair: check light, oxygen sensors, oxygen sensor

Question
OBD-11 read code PO135-upstream heated O2 sensor heater fault. Initially I replace both upstream and downstream Oxygen O2 sensors and I still have the check light and the same PO135 code. What's next?  Thanks

Answer
Joe,

Then, it is probably the relay that is the problem.  The oxygen sensor is heated to reduce the time it takes to get it to operating temperature.  There is a timed relay.  If the relay is defective you will get the code.  I would look under the hood at the relay box and replace the one that feeds the oxygen sensors.