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Discussion Starter #1
I need help determining which brand of O2 sensorS to buy for my 2006 350Z. High tec OBD diagnostic code reader reveals service engine light stays on due to codes related to O2 sensors. My z had an OSIRIS performance dyno tune several years ago as well as aftermarket Berk Technology free flow catalytic converters installed and an INVIDIA GEMINI dual cat back exhaust installed. I would hate to buy 4 new O2 sensors and have the service engine light stay on due to the cats and exhaust. BOSCH are the most expensive O2 sensors but claim to truly be OEM. What about brands such as AC DELCO, NTK, and DENSO. Any 350Z owner with knowledge in this conundrum would greatly be appreciated.
Stu
 

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Only oxygen sensors I ever use in Nissans (or any other Asian make vehicle) is NTK or Denso. NTK makes most of the OE sensors for Nissan and is the same company as NGK, who makes most of the OE spark plugs for Nissan. Denso was once owned by Toyota and makes some of the Nissan OE oxygen sensors and spark plugs and most of the sensors and plugs for Toyota.
It's rare that you ever need to replace all of the oxygen sensors or air/fuel sensors (which is what your upstream sensors actually are and operate a little differently than conventional O2 sensors). P0420/P0430 catalyst efficiency codes are triggered by the ECM when it determines the catalytic converter(s) situated between the upstream and downstream oxygen sensors are not breaking down exhaust emissions efficiently. It does this by comparing the upstream and downstream sensor readings for a given bank. The rich to lean switching frequencies of the sensors is around 2:1 on an efficient converter and around 1:1 on a non-efficient converter. Cat-back exhaust won't cause catalyst efficiency codes but sometimes aftermarket catalytic converters do; they don't always break down the emissions as efficiently as original equipment converters. Sometimes you can "trick" the ECM so it won't trigger the codes by using spacers or CEL eliminators on the rear oxygen sensors, which pull the element partially out of the exhaust stream. If you live in a state like CA that has strict inspections, such spacers can cause the vehicle to fail inspection.
 

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Thank you for this most informative reply. I replaced all four sensors and did a manual reset of the check engine light. Check engine light stays off. I used two Denso for the upstream and two NTK for the downstream. Several years ago I also had an OSIRIS performance dyno tune done by ZFever in Tampa. I assume that reprograms the ECU with performance parameters. I've often wondered if the check engine light stayed on due to the OSIRIS dyno tune, the free flow cats, the O2 sensors, or the Mishimoto low temp thermostat. The low temp thermostat has been well documented on several 350Z forums as the culprit. I recently replaced it with an OEM thermostat. I can't tell any difference in how it runs, sounds, and performs since I put the new O2 sensors in. Maybe I just wasted $278 on four new sensors.
Stu
 
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