O2 sensor problem with my 06 Xterra! HELP!

Maintenance/Repairs
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1

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!

2

Your post is very lengthy and it’s very difficult to wade through a long problem like this; especially with some missing info. I don’t mean this to be too critical because I can certainly see where you’ve been through hxxx with this vehicle.

Where are you at with the spark plugs and coils on this vehicle? A single misfiring spark plug can create issues related to O2 codes and it would surprise me a bit if your mechanic and the dealer has not considered this.

Regarding the code for the misfire on 2, 4, and 6 do you know exactly what code that was? I would think that it should be 302, 304, and 306 instead of one code.

The part about 5 volts being present on something is also confusing without knowing what wire and sensor is being discussed. Most sensors use a 5 volt reference and that’s normal.

I’m sorry that I can’t be of more help at this point and I also hate to be too critical of other mechanics without being in their shoes but replacing O2 sensors en masse by the crate is flat wrong.

3

I had 02 sensor code problems a while back on my pickup. I have since come to the conclusion that the CEL system used on modern vehicles was poorly designed. There’s nothing you can do about it except find a good mechanic who is willing to find the “real” problem.

In the last couple of years I have seen many CEL codes indicating bad 02 sensors. I just reset the code and see what comes back next. I have repaired several vehicles with 02 sensor fault codes and the real problem was always corrected with another part. I have not replaced an 02 sensor to date. I have replaced air filters, gas caps, TPS, MAF, bad wiring and cleaned EGR valves.

The CEL system can only tell you that something is wrong with the engine. It’s can’t narrow the problem down to a single part. That’s where a good mechanic earns his money.

4

I don’t claim to be an expert, but much of this is familiar. My '03 Xterra spent 6 weeks in the shop earlier this year. At the end of the day it turned out the distributor was bad, and replacing it fixed the idle problems, the catalyti converter efficency errors, misfires , O2 sensor etc.

What you have to keep in mind is that diagnostic codes and repair actions are based upon the EXPECTED failures, When things that are not expected to fail, fail, it can and often does lead to ‘wild goose chases’… If your shop has an emission analyser, you might have them check for large amounts of unburned hydrocarbons in the exhaust stream. That’s the tip that it may be an ignition issue.By the way the car only had 40,000 miles on it, so failure of the distributor was very long on list of possibilities,

5

If I was working on this I would be using a scope or scanner to check the O2 sensor signal waveforms. Perhaps the techs have already done that. I assume your mention of the 5 volts is because it is being seen on the O2 sensor lead to the ECU and if so that would seem to possibly indicate a open connection to the sensor. But that seems like too easy of an answer to this problem. Another possible explanation for the 5 volts is a bridged wire connection on the O2 sensor lead and the 5 volt supply coming from the ECU. Maybe there are some burned wires near the exhaust pipes and wires are being crossed that shouldn’t be. Disconnect the ECU connections and check the resistance between the 5 volt source lead and the O2 sensor signal lead on the wire connectors for the ECU. If there is a low resistance between those points then some wiring is crossed somewhere. That basically is what the factory techs are also saying to you and if that proves to be the case, using a factory wiring manual as a reference, it shouldn’t be too hard to find the bad spot inside the harness and repair it. The quote they gave you to fix this is your typical dealer quote it seems to me. They will charge you an outrageous amount of money to cover their excessive labor and parts costs.

You may want to take this problem to a shop that specializes in electrical problems.
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6

The automotive repair industry is slowly losing its ability to repair electronic problems that plague many of today’s cars…Many consumers feel they are better off simply leasing a vehicle in perpetuity and letting someone else worry about problems like this…A monthly car payment that never ends…Others simply reset the light and head for dealer to trade the unfixable car in on a new one… It’s about time consumers demanded a 10 year, 100K mile warranty on CEL problems. This would force the manufacturers to clean up their act and get it right…

7

Yeah, I don’t see this as progress either.
To make things work better through technology is fantastic but if only few can properly diagnose it, what’s the point?

8

With today’s vehicles you not only need highly skilled mechanics you also need folks that are very skilled in electronic trouble shooting. I think a good shop should have at least one person around that can be referred to for cases like this.

9

I bought it in march and it had a check engine light for a cylinder 1 misfire. Well the dealership guy got it “fixed”…test drove it, it was fine… Bought it and on the way home it was rough idleing at red lights. Called the guy back up and he took it to some crappy mechanic and they replaced a coil and another spark plug… Same as what the dealer did to get the check engine light to go away… Anyways took it home and now I have a P0420 and for them to change spark plugs or coils on my Xterra they have to remove the intake manifold… So im not sure if I have a vacuum leak or a issue with my catalytic converter or if its the O2.