Question

G35 3.5 installed 4-new 02 sensors for front & rear & still getting p0037 & p0138 codes. ideas or suggestions?

Answer 1

You didn't need to replaced all sensors, both codes are for the Rear Sensor Bank 1.

P0037 INFINITI - HO2S12 Heater Control Circuit Low

Read more: https://www.autocodes.com/p0037_infiniti.html

P0138 INFINITI - HO2S12 Circuit High Voltage

Read more: https://www.autocodes.com/p0138_infiniti.html

As you can see from the attached image, the circuit is very simple, and there is no other component betwen the sensor and the Engine Control Module (ECM). If the sensor is OK then the problem is either the wire harness or the ECM. You should replaced the Rear Sensor Bank 1 again, it's common to have bad new sensor. Bank 1 is passenger side. Did you use factory sensors?