Hi ya'll this is my first post on here so go easy on me, I'd also like to apologize for rambling in advance, ADHD makes my thoughts bounce around like a ping pong ball at a frat party beer pong table. I have an 03 G35 Sedan 6mt. I am having issues with my o2 sensors. I have codes telling me that the bank 1 and 2 primary and secondary sensors have circuit codes. I have replaced all the sensors and cleared the codes, I have also replaced the MAF because it was bad (unrelated issue). All parts were OEM from the dealer because I know o2 sensors can be picky when it comes to resistance. The codes have been set since I got the car. Ill include a list of all the work I've done to the vehicle in the year I've had it if anybody wants to know (its long and I won't waste time). Anyway back to the topic at hand. I was curious if anybody has run into the same issue. I have some friends telling me that I could have an intake leak however that is unlikely since I got new gaskets for the intake when I did my valve covers and I have not been able to find one with my smoke machine.
I have as stated before replaced the sensors with dealer sensors and even probed the wires for resistance in the sensor harness and the vehicles wiring harness and the resistance shows good so I am confused as to why they are presenting an issue. Any help would be appreciated, I have my annual inspection coming up in a couple of months and I can't get it illegally inspected anymore as my guy no longer does inspections

 

What codes EXACTLY.

 

I am not entirely sure off the top of my head, I’ll pull codes whenever I get home and let you know

 

Did you reset the ECU after replacing the parts?? That's the first thing I would try. Does the car have any performance issues?

 

I ended up getting another ECU shortly after getting the car because it had internal issues (it was fried) and I did get the new one programmed. The codes were consistent from the original ECU and I even did a relearn on the O2 sensors using one of my buddies scanners. The vehicle does not seem to have any performance issues, I did get a lot of back pressure shortly after I got it but that is because the cats were clogged, gutted them out and threw some spacers on the o2 sensors and she runs great.
just can’t get the damn engine light off. Comes back within 20 miles of being cleared and will run differently with it cleared, it will almost act as if traction control is kicking in upon aggressive acceleration, but again all codes present are for o2 sensors. Id also like to note that when the codes come back it runs great again with no hesitation
I didn’t get a chance to pull codes tonight as I got off work late (I daily a company vehicle and the G is my weekend warrior car lol)

 

Alright y’all, it was a crazy week so I was unable to get out to my car to pull codes but I finally got em, codes are as follows P1276,P0138, P0158
Any help would be appreciated

 

Alright y’all, it was a crazy week so I was unable to get out to my car to pull codes but I finally got em, codes are as follows P1276,P0138, P0158
Any help would be appreciated

 

Sounds like you might have damaged/melted wires between the ECM and the O2 sensors. Did everything look fine on the harness when you swapped the sensors?

What kind of non-foulers did you use for the downstream sensors? It's not uncommon to require 2 per side. Drill one set out so it's basically just an extension for the first set, screw them together. This moves the sensor further away from the exhaust flow but you will DEFINITELY have catalyst efficiency codes otherwise if you hollow out the cats.

 

I did not see any melted wires when I changed the sensors out as they are protected by loom. I don’t remember the exact spacers I used, they were from amazon and fairly cheap, I will try to increase the distance of the sensor from the cat and see if that does anything 👍🏼

 

You want the style of spacers that look like this, a restriction hole and the longer style. You should also hook up an OBD2 scanner that does real-time data and watch the upstream O2 sensors cycle to make sure they're working. If you see a flatlined signal then you either have a dead sensor or bad wiring. Easy enough to ring out the wires to make sure they're not screwed up, pin #'s on the ECM harness are listed in the FSM.

 

ill order some of those today, do you by chance know what section in the FSM that I can find this info? I looked yesterday and couldn’t find anything explaining the pin out diagrams

 

EC - Engine Controls, look up the DTC's you're getting and they will give you a harness/wire number. Then you can reference PG - Power and Grounding for more details like wire colors, harness pictures, etc. Most everything you should need is under EC though.

Also that code P1276 is not a valid code for the G35, I suspect your OBD2 scanner doesn't support protocol ISO 9141-2 which is needed for these vehicles.

 

The scanner pulls accurate codes and will give a rough troubleshoot area (B1S1 O2 Sensor Fault) and I can select Nissan as the make on the p1276 but I does not give any display on what it could be, had to take that and throw it to ole google. I’ll check out the FSM and start tracing wires.
by chance do you know off hand where the o2 sensors ground out at? Is it the ground strap off the exhaust, or is it somewhere else?

if the rear o2 sensors off the cats use that as a ground there may be a grounding issue, my exhaust gasket off of the muffler (where the strap connects) was leaking and bugging me so instead of being patient and ordering a new gasket I just threw some high temp gasket maker and called it good. Could this have weakened the ground to throw codes?

 

The proper protocol scanner will give you the actual DTC being sent by the ECM. They will be listed in the FSM, an unlisted code is because it's using a different protocol and it's finding the "closest match", P1276 is not a valid DTC for this ECM.

P-Powertrain
1-OEM specific
2-Fuel system
76-specific error

Since it's an OEM specific code it really does need the proper protocol to read it, this is pretty common since there are almost a dozen different protocols, still helps to have something with ISO9141-2 when you're working on these vehicles, it's probably just using ISO14230 which is far more common.

Using a realtime scanner to watch voltage fluctuations will tell you if the sensor is working, since you have drastic changes in performance I'm guessing it's not working at all and when it errors out and "runs better" it's because it is back in open-loop fuel mode.

The downstream O2 sensors are grounded on the black/yellow wire. There's a splice somewhere in the harness but I'm not sure where, they get their ground from the same pin on the ECM. However if you have exhaust leaks that will DEFINITELY cause O2 sensor codes like this but it sounds like your leak is downstream from all this, probably being caused by the hollowed out cats and non-foulers will help get rid of the code usually. Either way you can watch voltage changes on the B2O2 and B1O2 sensors to verify they are cycling as well. Keep the rpm's up at like 4k while you're reading those sensors.

 

Some scanners that don't offer real-time display will instead use things like an "O2 sensor test" or "emissions ready test" which can help pinpoint what the actual problem is with that upstream A/F sensor.