I have a 06 Xterra with a O2 problem that has been going on for over a year and a half! my mechanic has been on this car for over a year and now it has been at Nissan for over 2 months. no one can seem to figure out what is happening!!! here is the story from the get go:
I did a fuel injection servicing about a couple of years ago. a couple of months after that, the service engine light came up and I had my mechanics look at the code and it turned out to be the catalytic convertor (driver side). we tried to do another fuel injector clean up to see if it would go away; and it did for a month so so, and it would come back on for a week, and if i drove it for a while, it would go away. this kept on going for a few months.
I gave in to replace the O2 sensors with aftermarket sensors. this worked for a month or so. no issues and it seemed all was great! then, the service engine light came up again, and this time, the temperature (upstream and downstream) of the catalytic convertor (driver side) was way off! so I replaced both convertors. the car was driving great for a couple of months and then, the service engine light came up again! so, my mechanic replaced the O2 sensors (all of them).
A couple of weeks go by, and guess what? the light comes back on! same code: fuel air sensor issue! long story short, he replaced the O2 sensors 6 times (at his cost) and the last time with original Nissan parts. every time he would replace the sensors, it would take a couple of days to a week for the service engine light to come up.
About three months ago, the car started to run really rough and shaking like crazy! the code was for a misfire for cylinder 2, 4 and 6! my mechanic gave up and so i took the car to Nissan for a diagnostic. obviously, the code was cleared before taking it there, but by the time i was there, there were no issues with the truck! since they couldn’t find any issues, they told me to drop it off when there’s a problem.
I barely drove it out of the lot, when the light came on again! I left the truck with them, and after three days of diagnostic, they told me it was the harness! My mechanic picked the truck up (he paid for the diagnostic and offered to replace the harness for free). he did testing on all of the rest that Nissan claimed a short was present ,and he showed me that there were no issues with the wires! The resistance was 0.5 ohms for all wires!
We took it back to Nissan and they held the truck for 1 more week, and they said it was an O2 sensor issue!!! So my mechanic bought O2 sensors from them, reinstalled the sensors, and in less than 30 minutes after O2 replacement, the service engine light came up!
I took it to Nissan (over 2 months ago) and they have been looking at it and dealing with the Nissan technical excellence center (or something of that sort) to eliminate issues. So far, they tested the manifolds for a minuscule hole that was making the sensor read wrong, and the computer, the relay, the front harness and have nothing to report! They are puzzled and now they claim that the secondary harness (the one that goes from the main connector through the firewall) needs to be replaced at roughly $4000!!! This doesn’t make sense! They believe that there’s feedback that makes the sensor read 5 volts right away! I think the computer that sends signal for power is bad, they claim it isn’t! All signs (as far as I’m concerned) point to a software issue not hardware! The frequency of issues has increased and misfire codes (that were nonexistent) has me convinced that we are not dealing with a mechanical issue! PLEASE HELP ME BEFORE I BURN THIS TRUCK TO THE GROUND!