P0136 CEL 240sx, need help!

[Grim]

maybe someone here with O2 sensor experience can chime in.

Im getting a code P0136 O2 Circuit (Bank 1, Oxygen 2)

I replaced both my upstream and down stream O2 and the code is still there.
Upstream is Borsh and Downstream is NTK

What else do I need to look for?

[mb_]

Not sure about 240's but all the cars I've had a CEL on, I had to clear it after repairs were done

[Grim]

disconnecting battery doesnt work?

[jing]

Shoddy wiring?
Posted via RS Mobile

[Grim]

^ im guessing...
gonna look under the car 2 see if the wiring is messed up later

[mb_]

Originally Posted by Grim

disconnecting battery doesnt work?

I've never tried it with o2 sensors but I've heard it doesn't work sometimes

[Grim]

ill get under the car tomorrow and pray its not the harness thats messed up

[Qmx323]

Might need a reader to clear that code.

I replaced my O2 Sensor on the G20 and code stuck until I plugged a OBD2 reader and cleared it.

[Fafine]

should be gone if you can get a reader to clear it

[Grim]

came back after getting it cleared within 15mins.

im just thinking... could my downpipe be defective?
would that throw a P0136 code?

the OE down pipe i got was messed up... the O2 sensor broke and i had to get it tapped out and reweld a insert... could that screw up the reading of the O2?

i replaced my O2 with NTK 24545 which is specified for my car....
im starting to lose hope...... the wiring looks fine *to my understanding*

should i try and just get a new downpipe and test my luck?

[SpeedFactor]

Are you running a cat in the car? If the O2 is reading the same pre and post cat voltages, a CEL may come on. if you are runing a cat, it might be time for a new one

[Grim]

i replaced my cat with a magnaflow, and installed a OE downpipe with the pre cat.
the previous set up just had a downpipe with a cat welded on.

i went under the car and checked the wiring, and there seem to be no sign of corrosion or shoddy business..
i had the car on and tried to check for any noticable exhaust leak from the header downwards and nothing..........

[jing]

IIRC what you refer to as a "cat" that was replaced with a Magnaflow was actually a dummy cat

[Grim]

dummy cat?

exhaust manifold *O2sensor* downpipe *precat* *O2sensor* magnaflow cat, exhaust

would the magnaflow cat affect the 2nd o2 reading tho?

[SpeedFactor]

Upstream o2, main cat then downstream o2. The o2 shouldn't be between the pre cats.

[Grim]

the OE pipe was designed like that

[SpeedFactor]

I might be wrong but i didnt think pre-OBDII 240's had a pre-cat. i think the main cat after the secondary o2 would be redundant as far as engine managment controls are concerend. most likely it would be:

downpipe - o2 - cat - secondary o2 - silencer(or some sort of exhaust pulsation dampener)

please feel free to correct me if im wrong

[Grim]

Thanks for your help SpeedFactor.

but the 1997 240sx exhaust system goes in an order like so.

Engine -> Exhaust manifold with O2 -> pre cat -> 2.25" pipe ->O2 attached on pipe -> main cat -> resonator - > more pipe -> muffler -> tip

[Qmx323]

I think jing is referring to the fact that the magnaflow cat you put in isn't really a cat at all. (lol)

Its could be one of those "high-flow" cats that are basically test pipes.

o2a reads xx, xx passes through "uncatalysed", xx remains xx, o2b reads xx, throws code because it thinks your cat is not functioning properly.

In my 92, after replacing the cat with a highflow, no codes were thrown because my 92 only had one o2, which was pre-cat

[Grim]

hmmmm.......
should i try replacing the cat?
or maybe get the megan down pipe that comes with a precat / cat?


btw: my cat convert light blinks for like a bit every time i turn on the car then goes away....
maybe it is the cat deficency




this is the OE pipe i bought and installed. I looked at the Pre cat prior to install and the pre cat condition looked good.
mind you, i am a complete noob.. so i could be very wrong and wasted 50usd on that stupid OE pipe

[jing]

Originally Posted by Qmx323

I think jing is referring to the fact that the magnaflow cat you put in isn't really a cat at all. (lol)

Its could be one of those "high-flow" cats that are basically test pipes.

o2a reads xx, xx passes through "uncatalysed", xx remains xx, o2b reads xx, throws code because it thinks your cat is not functioning properly.

In my 92, after replacing the cat with a highflow, no codes were thrown because my 92 only had one o2, which was pre-cat

Ish, what I meant was that basically he has 2 cats now, when S14's only came with one from the factory. The OE one at the tail end of the downpipe, and now he replaced the dummy cat with an actual Magnaflow one. Not sure if the 2nd aftermarket cat is the one causing the issues or not, though I know that is unneeded.

[Grim]

this is the S14 exhaust diagram.
pulled out from nissanparts.cc

[SpeedFactor]

We cant really be sure of the problem until we know what the down stream o2 is doing. is it running rich? 1.0V, or lean? 0.1V. Seeing how the o2 is new it might be an engine problem.

[Grim]

how can i check if its engine failure?
the cat light blinks, im guessing the ...... pre cat? is not functional?

[devenprasad]

The Attached File from Mitchell on Demand; May be of interest to you.