I have a 97 Nissan Pathfinder - swapped the spark plugs on May 2023 (Bosch), the car ran without any issues until December 2023. I got an MIL light, plugged the OBD - it started with the front passenger sensor o2 giving issues, eventually through the time all 4 gave out. Around the same time of May I swapped the spark plugs as they were heavily carboned, now that I am swapping all 4 sensors, what can cause for this to carbon build up happen? Air Filter is relatively new as well.

Carbon-plugged O2's really only come from one thing, running unnecessarily rich. That can have a number of causes. Check your short and long term fuel trims to start, that will give you a clue.

If the trims read negative then you have excess fuel coming in from somewhere and the ECM is trying to compensate lean. That can be from leaky injectors, high fuel pressure, or a blown diaphragm in the fuel pressure regulator. The VG Pathies are notorious for the latter.

If the trims are normal then you may have either an engine temperature (ECT) or intake air temperature (IAT) sensor that's lying to the ECM, making it think the engine or incoming charge are colder than they really are and preventing it from going into closed-loop operation. Check the ECT with a scan tool, I'm pretty sure your '97 will have separate ECT and gauge senders like most older Nissans. That means what the ECM sees and what the gauge reads can be completely different. Since this apparently started after a plug change, it's also possible those Bosches are simply the wrong heat range. To be frank, I don't trust anything Bosch on a Nissan engine. Your originals were either Denso or NGK, and you should keep it that way.

If the trims read positive then you probably have a MAF issue, the ECM is wrongly assessing the incoming airflow and then correcting lean once it gets into closed-loop.

Appreciate the information. As I was swapping the o2 sensors I was able to tell that both of the passenger side was carbon present. Specially the down stream sensors, however once I got to the driver side I notice that the protective sleeve for the down stream was stripped and wires were exposed. No sure if that caused the wires to get burnt out and caused everything to go hay wired. I notice that the previous mechanic that swapped them - did not used the bracket to place the wires zip ties in its place.

Right now I am having issues on swapping the driver side front o2 sensor as space is limited and little to no room for sockets to enter.

Situation update - just finished installing all 4 sensors, codes disappeared as I had the full battery disconnected. The car did warmed up really well, no codes after operating temperatures.
However once I was pulling off the drive way the car did began to sputter and gained its power. However once I was driving 2 blocks away from my house bam - car shuts off. The MIL came on and these are the codes that I got.

These are the six codes I got according to the OBD2 sensor:
P0161
P0100
P0135
P0141
P0155
P0100

Except for the P0100, those are all codes for the O2 sensor heaters. Make sure you didn't blow fuse #25 during replacement, that supplies all four heaters. If the fuse is good then I'd say the most likely cause is the wrong parts. Dunno what brand you bought, but if they aren't Denso, NTK, or Hitachi, you can end up pulling your hair out.

P0100 is a flatline code for your MAF, it can happen from the cycling the key with the MAF disconnected. See if it will erase, if it does then forget about it. If it doesn't, see EC-99 here for how to diagnose it:
https://www.nicoclub.com/service-manual ... 7%2Fec.pdf

I got Bosch for the sensors in which according to some research they are the OEM suppliers for the vehicle year 1997.

P0100 has been giving me issues in the past as well, battery was completely disconnected when I swap them, connected the positive terminal first then the negative. I will give the fuses a look hopefully it is all good.


Someone told me to give the MAF a clean with a cleaner (MAF cleaner), give it time to dry, plug it in, and see if that fixes it. If not then most likely it will be that I have to replace the unit. Sadly the sensor Hitachi is no longer available - I will have to buy the whole housing with it.

The ones I got are Bosch part# 13228/13257 + 13224/13264

There's no real equivalent to a P0101 on older stuff, so P0100 covers a multitude of sins, open, short, and malperformance. The ECM can't tell you which, but a voltmeter generally can. Check it against the specs in the FSM, you may actually have a wiring issue and not a bad MAF. Not that cleaning the MAF is ever a bad idea, I'd definitely do that even if the code is an artifact.

Some of the older stuff did use Bosch, so you may be right, but Bosch as a company just isn't what they used to be. Ever since they got into consumer electronics they've been on a downhill slide. Nissan had to recall a gazillion of their ABS's on the Max, Murano, and R52 Pathy, and they used to be the last word in ABS. Their radars on the '16~'19 models were nothing but trouble, and their navis on the '14~'15 Altimas went through 4 reflash bulletins before they finally unscrewed them. I don't actually think we've seen a single new model navi or radio from them that didn't arrive buggy. So forgive my skepticism, but I just don't trust the brand anymore. Denso and NGK rarely make my head hurt.

VStar650CL wrote: ↑

Wed May 29, 2024 7:40 pm

There's no real equivalent to a P0101 on older stuff, so P0100 covers a multitude of sins, open, short, and malperformance. The ECM can't tell you which, but a voltmeter generally can. Check it against the specs in the FSM, you may actually have a wiring issue and not a bad MAF. Not that cleaning the MAF is ever a bad idea, I'd definitely do that even if the code is an artifact.

Some of the older stuff did use Bosch, so you may be right, but Bosch as a company just isn't what they used to be. Ever since they got into consumer electronics they've been on a downhill slide. Nissan had to recall a gazillion of their ABS's on the Max, Murano, and R52 Pathy, and they used to be the last word in ABS. Their radars on the '16~'19 models were nothing but trouble, and their navis on the '14~'15 Altimas went through 4 reflash bulletins before they finally unscrewed them. I don't actually think we've seen a single new model navi or radio from them that didn't arrive buggy. So forgive my skepticism, but I just don't trust the brand anymore. Denso and NGK rarely make my head hurt.

Ha! I have the ABS light on too lmao! Nissan Part Deal just want way too much for the o2 sensors - easily $400 for all 4. I had the same issue last year with the o2 sensors, I actually found pictures where it threw me the P0100 also. I am going to go to the part store tomorrow, get me a set of fuses, MAP cleaner, and then there is a Catholic church 3 blocks down. Going to get a rosary, holy water, in incense to see if that helps too.

Nightmare is over! So here is the solution and symptoms on my 97 Nissan Pathfinder SE:

On 2022 of December I got MIL (Check engine light) plug the OBD and it came out Bank 2 Sensor 2 o2 sensor. P0161 (o2 heater Circuit) in which ran good until 2023 the car began to rough idle.
Eventually the car would idle according to the live feed on my OBD2 from 800 RPM down to 450 RPM and would fluctuate from there. However the code will also be P0100 (which I completely ignore trusting the MAF would not be the problem). I swap the sensors with Bosch (which is the OEM supplier for this particular year) and the car ran fine (this was in May 2023). Months later (Dec 2023) the issue rinsed again the the P0161, P0100, and then PP0141 + P0155 + P0135. Car will run fine, once operating temp and on the highway (about 4~5 miles) the car would suddenly shut off. I would then put the car on N and turn it back on, would run a few miles (lucky it would stay on as long my foot was on the gas) and shut off when I stop. The car would throw the gears rough at times, I swap the sensors (thinking I got faulty ones). Ran the car, 2 block later, the car rough idle at idling and shut off, eventually struggle to start, smell of raw fuel. Diagnose again and same codes mentioned earlier. I cleaned the MAF sensor with the proper cleaner, saw there was some carbon on the probes (two small metal ones inside the sensor) cleaned it, cleaned the connectors and same seems fine but did not work. Eventually I gave it the benefit of the doubt - bought a new MAF from O'rileys (Hitachi - any other brand may cause the same issues). I remember my mechanics telling me Asian cars you have to go with OEM on the electronical parts, it is a must! Do not throw generic brands as they will misfire again. Trust me I learn this the hard way with my distributor a few years back. Installed the new MAF and bam! ran running, idling, and operating fine! I swap the whole housing and MAF sensor, cleaned the manifold intake, and no issues anymore. Hope this helps to those who encounter this issue. Please ensure to use the proper spark plugs, wires, sensors, on all electronical parts. Do some research of find the approved manufactures for the car in order to avoid double the work.