Hey everyone! I’ve been dealing with a stubborn P2A03 (Bank 2 Sensor 1) oxygen sensor code on my Z for a few months- if not when I bought her 2~ years ago. Before I get into specifics, here is some info on the car.

Quick info:

• 2006 Touring Roadster
  
• Automatic, VQ35DE
  - The chassis has 242,000 miles, but the previous owner told me that the engine was replaced (CarFax report does corroborate this) and told me that the replacement engine had something like 100,000 miles. Whether that part is true or not is unknown.
  

I’ve done a lot of repairs and mods, but to keep things relevant, I’ve only listed the engine-related ones below. The items specifically done to remove the P2A03 code are bolded. Let me know if you’d like the full list of everything else.

• Spark Plugs (Oct '24)
  
• Intake Manifold Gasket, Fuel Injector O-Rings, Injector Harness, misc vac lines, Camshaft & Knock Sensors (3/27/24)
  
• Flashark Catback exhaust (og exhaust was leaking a ton) + ISR High-Flow Cats (the car originally had test pipes) + Rear O2 Sensors (Walkers) (9/20/24)
  
• All 6 Ignition Coils (11/23/24)
  
• PCV Kit + Upstream O2 Sensors (Walkers) (4/13/24)
  
• 75mm Z1 Throttle Body, MAF, also replaced the airbox to Throttle Body rubber intake with a metal one from Z1. (12/25/24)
  
• I replaced the Walker sensor on Bank 2, Sensor 1 O2 Sensor with a OEM Denso one – just replaced today (4/13/25)
  

The code has been on for a long time, so I don’t think any of the mods are causing it—but I could be wrong. A well-rated exhaust shop recently checked for leaks and found nothing, which made me hopeful that replacing the Walker sensor with a Denso would remedy the issue.

The car runs strong and smooth, with no odd revving or anything like that. There are also zero other codes. In a day or two, I’ll attach my obd2 reader's live feed when my car was idling—I noticed the voltage on the O2 sensors varies by bank, with the bank 2 not fluctuating as often as bank 1, and the fuel trim shows "Lean." Not sure if that’s normal or part of the issue.

Would really appreciate any insight. I'd also like to specify that I am not looking to break the bank here- i.e., replace every single sensor w/OEM unless everything else cheaper has been suggested/tried.

Small Update: the code is gone after replacing the EVAP Purge Valve for a different issue, which is now giving me a code. Probably didn't fix it, more of it's being hidden for now while the evap purge valve is giving the ecu a code.

 

Update: I ended up taking out the battery in my z, and reconnecting it a few hours later (I needed the battery for a parts car) and unsurprisingly all the CEL codes were gone, including P2A03 which has continued to stay on since I made the original post. I also replaced the negative battery cable with a good condition OEM one from said parts car. After about 130~ miles of driving since I took the battery out Monday, the P2A03 code hasn't shown up, instead being replaced by P0157 (current) and P0158 (historical) which are both O2 sensor codes. It's even more interesting since those codes correspond to the Bank 2, Sensor 2 instead of Sensor 1 like what P2A03 is for. I'm sure all of the O2 sensor codes are being triggered by the same problem, but I figured I would share this info anyways.