Need help with oxygen sensor issue..Which side is which?

[mateen110]

2001 nissan pathfinder with 110k. I was thrown a code "p0140"-- which reads "o2 sensor no activity (bank 1 sensor 2)


Took it to the local mechanic and he unplugged the passenger side, front sensor to see if it was the front or rear. Now we get two codes. We get the original p0140 o2 sensor no activity and we get a new "P0141 o2 sensor heater malfunction (bank 1 sensor 2).


It is my understanding that sensor 2 is post cat. If that is the case, then why would unplugging the front sensor throw codes for a rear sensor?

Thanks in advance.

[fueler]

i dont know

[mateen110]

Bank 2 is drivers side, and bank 1 is passenger side

post5979237.html#p5979237

[fueler]

http://www.nicoclub.com/FSM/pathfinder/2001/ec.pdf

start at page 279... everything you need to know, directly from nissan & specifically for the 2001 pathfinder.

Remember, NICO has the factory service manuals for all nissans, in the HOW-TO pinned at the top of our forum!

It's my go-to for everything!!

[Towncivilian]

Bank 1 is the side with the #1 cylinder, and bank 2 is the side with the #2 cylinder. So, bank 1 = passenger side, bank 2 = driver's side.

Here are the harness connector locations for the O2 sensors to aid in your diagnosis:

[mateen110]

Bank 1 is the side with the #1 cylinder, and bank 2 is the side with the #2 cylinder. So, bank 1 = passenger side, bank 2 = driver's side.

Here are the harness connector locations for the O2 sensors to aid in your diagnosis:

So if I removed bank 1 sensor 1...why is the car throwing a code for bank 1 sensor 2?

[Towncivilian]

The rear oxygen sensor will take over for the upstream one if it is malfunctioning (or in your case, disconnected). However, if the heater for the rear O2 was malfunctioning it should have thrown a code previously along with the first P0140 "O2 sensor no activity" code. Strange.

Perhaps you should clear the codes and see which codes return.

Bosch is the manufacturer of the OEM sensor. A rear O2 sensor was throwing P0158 (heater high voltage) so I replaced it with an OE-type Bosch replacement I bought from Advance Auto Parts after a discount code for $50. The passenger side post-cat sensor shouldn't cost much more than $50 after a discount code, and you can replace it yourself if you're so inclined.

[fueler]

a few weeks ago i needed an o2 sensor for a honda and amazon actually had the best deal out of everybody... worth checking out

[Towncivilian]

OP, please provide the manufacturing date of your Pathfinder so I can determine the correct O2 sensor for your vehicle.

[mateen110]

06/00, much appreciated.

[Towncivilian]

Amazon is indeed the cheapest in your case as fueler suggested. This is the sensor you need. If you want to tackle the replacement yourself, you will need a 22mm or 7/8" oxygen sensor socket. Read my experience with rear O2 sensor replacement and tips from ARKQX33V6. I did it in the dark - the process will go much more smoothly during the day I'd imagine.

You also have a 2001.0 model year Pathfinder, for your information. The 2001.5 model year revision (which began starting 08/00 mfg. date) included revised spark plug coil packs to correct issues that plagued the 2001.0 model year. I'm not saying your coil packs will fail, but I've seen many more cases here of P1320 (ignition signal) codes without any other specific cylinder ignition codes with 2001.0 model year Pathfinders compared to newer models - the suggested fix is often replacement of all coil packs and sometimes spark plugs, which is quite expensive even when aftermarket coil packs are used. My 2001.5 has been free of coil pack issues for 130k miles now.

[mateen110]

thank you so much for that information. I am learning so much on this site already. So you think that it is indeed the rear sensor...not the front one?

and ill be on the lookout for the p1320 codes!

[Towncivilian]

Bank 1 sensor 2 is definitely the rear (post-catalytic converter) oxygen sensor on the passenger's side.

If you want additional confirmation, you can reset the codes (disconnecting the battery for several minutes should do the trick if you have no other means available) with all O2 sensors plugged in and see which codes pop up after several trips. In my case, resetting the code after its first sighting took around 30-40 miles of driving for it to pop back up; resetting again did the same thing, so I just replaced the sensor and all is well now.

As for the drop in your mileage, how many miles do you have on this Pathfinder? Perhaps try running some fuel system cleaner like Redline SI-1, Chevron Techron, or Gumout with Regane. All three of these contain a significant amount of polyether amines, which is a detergent co-developed by Chevron and BMW to effectively clean fuel deposits without leaving behind deposits of its own as solvents and other cleaners do. Redline SI-1 contains the most PEA out of the three. If the fuel filter hasn't been replaced to your knowledge, replace it after running the fuel system cleaner. There is a replacement guide here - replace using a Wix 33023, or a NAPA Gold 3023. Ensure the air filter isn't completely clogged. You should also be running at least 91 octane fuel for the best performance - the difference only amounts to several dollars per fill-up. You can read more about octane in this article if you wish.