o2 issues. out of ideas.

[Twilight sentra tuner]

what's up guys? hey i've got some problems with the car. it's throwing circuit malfunction codes for the o2 sensors. i believe the codes are p0135, p0141, p0155, p0161. i'm not really worried a/b the last two codes because they just let me know if the cats are working or not. (pre). the first two are the ones giving me problems. my car is a 00' gxe with a CAI, OBX header, VRS 2.25 cat back SS with a high flow cat converter. also has a voltage stabilizer and grounding kit. getting ready to go put a throttle body spacer on. but any help would be greatly appreciated. thanks in advance.

[RED_DET]

Here are the list of codes and what malfunction causing them:

zerothread/209037

Have you replaced the o2 sensors? You more than likely getting the codes because of the after-market header.

[nametakennow]

You sure you put the sensors in the right order? 00 GXE's had 4 O2 sensors and are VERY sensitive to having them in the right order with the right spacing.

[Twilight sentra tuner]

in response to red det, i think you might be right a/b the header install. i've had nothing but problems since i installed it on. the link you set up is a little helpful. but didn't tell me why the codes are being thrown. i'm going to try your reset procedure and see where that goes. i wish i could reflash the system but nobody makes reflash software for that particular motor.

the o2 sensors are in the right positions. i had a thread going on a while back with the same scenario but was never answered. the bottom 2 o2 sensors are pointless in this situation. they're just telling me if my precats are working or not. but they really don't affect the performance. however i've seen other people with the same motor having a header on it and not having problems. just curious if a piggy back like the apexi safc or neo would help out or not.

thanks again in advance for your input.

[Twilight sentra tuner]

please don't ignore it this time. i'm coming here for help. not to write rhetorical questions.

[nametakennow]

We come here voluntarily to answer questions. Sometimes we don't get to things very quickly and, occasionally, they even fall by the wayside. There's no need to get impatient.

You're right, the rear O2s are just in regards to the precat. Personally, I'd find it annoying to have codes all the time if I could easily avoid them (and GA requires no codes to pass emissions). It'd also be easier to diagnose the issues you may be having with the front sensors without the rear ones throwing codes too. Feel free to utilize any of the methods I've described in the B15 Common Fixes thread in the Table of Contents in order to get rid of the codes for the rear sensors.

On to the issue at hand:

The reason I got on about the sensors being in the right order is because a number of QG18 owners have struggled with codes issues only to find out that they'd accidentally placed the sensors in the wrong order, or even too close together. I'm going to assume, however, that you have this right because you probably do.

A piggyback won't help. Your AF ratio is probably just fine, at least in terms of being close to factory specs (which is what your ECU wants). Actually, now that I look at the malfunction list, both these codes are heater codes, which have no bearing on what A/F your sensors are reading.

The most likely culprit for a heater code is that the sensor itself is bad. The other option is that it's wired incorrectly, but I assume that since inserting the front O2 sensors into an aftermarket header doesn't require any adjustments to the wiring harness, this probably isn't the case.

These are OEM sensors, right? Nissans are finicky, so if they're aftermarket (Bosch generic ones, for instance) they can easily fail and/or throw codes.

Are these the original sensors? If so, they're approaching 10 years old (your 2000 model year was most likely built in late 1999 or early 2000 at the latest), so failure isn't at all surprising.

[Twilight sentra tuner]

i apologize for my earlier statement. i just didn't want it to be thrown to the dirt again. ( not saying it's your fault.)

these are not the original o2 sensors. i tried replacing them once before but the problem still did not resolve itself. the sensors i'm running are bosch. and i know nissan and bosch don't mix to well in certain aspects. i'm not sure though what the oem sensor brand is. i'd assume ngk or denso but i'm not sure.

they are heater circuit malfunction codes. the only thing that i can think of is the fact that the header is disposing the exhaust faster than normal and based on the headers material that it's throwing the voltage current to the o2 sensors to sky rocket and go beyond what they're supposed to. the o2 sensors are supposed to be running between 0 and 1 volts but i assume that this number is higher than factory specs. that's what i can gather on it.

if you guys have anymore thoughts a/b the situation, let me know.

[nametakennow]

The conductivity difference of the different headers isn't enough to do anything. The difference in flow rate is also inconsequential.

The heater is essentially a resistor in the sensor that gets it up to operating temperature faster than exhaust gas flowing by otherwise would. O2 sensors only operate once they're warmed up, so in order to get a reading while the engine is cold, they utilize this setup and use electricity to warm up. A heater circuit malfunction means literally that - the circuit for the sensor's heater isn't connecting properly, thereby not allowing the sensor to heat up and start reading quickly.

If you had this with your stock sensors and have it again with aftermarket ones, the difference in brand probably isn't the issue.

Have you had your VIN run for the ECU foam recall? Could be a bad ECU throwing codes.