So I’ve got a base 04 350z. Cleared a bunch of codes after I bought it and I’m down to 2 codes P0037 and 31 for the heater circuits for both o2 sensors on bank 1 (passenger side). Swapped sensors, nothing. Swapped fuses, nothing. Swapped ECU, nothing. I was told by an aftermarket shop and a Nissan dealership that my ecu is not sending ground to the o2s so my guess is somewhere in the wiring loom there’s an issue. If anyone else has had this problem solved by other means I’d appreciate the wisdom but I’ve come down to swapping the whole engine harness itself. Is that a simple plug and play install or is it like the ecu with matching part numbers etc etc. Only had my z for a year and change so any pointers are appreciated !!

The harness did change a bit from year to year and model to model, I believe any 03-05 harness should plug right in. Usually two bad O2 signals on good O2 sensors means a dead cat. If it's the harness you could also pull the harness and unwrap the loom and trace the ground back, you'll find signal grounds crimped together and plit off at a couple of places in the loom.