Recently bought this 03 350z with a 2005 vq swap and 2006 transmission. I’m a new Z owner, and I love the car. It drives great, runs like a champ and has no mechanical problems at all. However, the car had a CEL (P0037) when I bought it. Replaced the sensor, checked wiring, etc and no luck. Code would come back after 2 key cycles. Brought it to a mechanic and they recommended a new ecu. Installed new ecu, had it reprogrammed and now I have a P0031 code (bank 1 sensor 1). I really don’t want to get rid of this car but it needs to get smogged!!

I might add that the harness and ecu on this car appear to be from the 2003 350z, as the 02 sensor plugs on the harness side are not wideband like the 2005 vq’s had. Not sure if this is the problem but since the ecu and harness seem to be from the 2003 z it shouldn’t throw a code if it can’t read wideband anyways. I don’t know a lot about how the swap was done unfortunately.

btw the part number for my ecu is PC mec31-510 same as the last one
car has about 200,000 miles

any help would be greatly appreciated, I don’t know a lot about Z’s and I’m new to the forum. Thanks!!!

 

Does your z have the heated or wideband sensors? The way to tell is to unplug it and look at the connections. Here's some pics of the difference - https://www.z1motorsports.com/oxygen...or-p-5466.html

I suspect the sensors are the issue, especially if it's an '03 ecu trying to read 05 sensors. I think getting these sensors sorted out would be easier than sorting out an 05 ecu for your z.

 

It has the 4 wire heated sensors. The harness itself looks modified, I’ll add some pics. Thanks for the reply!
must be a harness from the 03 with some splicing job.