My Z has been running poorly off and on, I got a chance to look at it today. The OBD2 Codes are for Bank 1 Sensor 1 Voltage High and Multiple cylinder misfire. So I checked the voltage from Sensor 1 Bank 1 and it's up around 1.2v!! Also, I was watching the fuel trim and as it reaches -25 the motor runs worse and worse. This all makes since, bad o2 is causing 1-3-5 cyl to run lean. At first I thought it was the coolant sensor, but this would affect both Banks.

So any thoughts before I am forced to spend $150 on a new O2?

 

Actually, Now i found BOTH O2 sensors are not working. I have a wideband, and I'm pretty sure it is correct. It shows 14.0-15.0 afr at idle. This is nuts! Does the ECU solely control the O2 sensors? Please see the screenshot attached.

 

actually bro they are just sensors. 02 sensors rarley go bad since all they do is monitor what your engine is putting out. so you say your running lean at idle 14.0 is pretty normal. your car will run a lot leaner when idling. i'd look at where ur misifire is coming from because 02 sensors won't cause your engine to misfire!! and as for your ect sensor those rarley go bad also. keep your sights on finding out why your car is misfiring and that should solve your problem. as for your ect before you fault your ect i would recomment puttine a thermostat in your car because all that sensor does is monitor the coolant temp and if it see's a difference in temp over a certain period of time the ecu will fault the ect but in reality the sensor is good it just has no way of telling you "oh your thermostat is stuck closed or stuck open" what all do you have done to your car. that may help in others helping you diagnose your car. hope this helps just my 2cents

 

Well, If my ECU thinks my o2 sensors are outputting 1.2v it thinks the mix is super rich when it's really not. So it will start trimming fuel, making the mix extra lean and causing misfires. So yes a bad o2 can cause a misfire.

Now I'm not sure it's the o2 or something in between the o2 and the ecu. If I pull the o2 fuse the voltages all drop to around .25, I plug it back in and the upstream o2 shows 1.25v and the downstream shows about .28v.

 

Just figured it out, Bank2 Sensor2 (Driver side downstream) went bad. If i unplug it all the other sensors start working. I've never seen this before, either this sensor is shorting out the entire heater circuit or nissan didn't design this stuff too well. Oh well, easy fix.

 

I find it hard to believe that if you have 2 bad O2 sensors that your car would start running lean. From my understanding most ECUs will run you rich as fail safe to protect your engine when the sensors go out because it's better to run rich than lean. Easiest way to find your problem is take it to a Nissan dealer. In 5 mins they can hook your car up and pull all the codes.

 

Nissan actually has a specific code for thermostat function, but I don't remember exactly what the # is. If the ecm thinks the car is not getting hot enough after a certain period of time it will set a code and turn on the engine light.

 

+1 to that. You may have a bad air flow meter thats causing everything downstream of it to act bad. Watch your short term fuel trim (A/F alpha to Nissan). Expressed as a percentage its normal range is 95%-105%. If its consistantly much higher(112% or more) or lower(89% and down) you need a new sensor.

 

Another reason that I don't think is your O2 sensor. Waht are the chances of both of them going bad at the same time? Second, Not sure on this one though. If you have your car at WOT it goes into close loop and it should run good.

I agree with Alrific, check you A/F meter.

 

I 3rd the motion. As for 2 sensors going out at the same time...I've seen it happen before...especially with Hybrids. But I'm not sure if the root cause of what I've seen was at the same time from the same source.