# failed emissions???



## Marius (Jun 17, 2004)

I have a 96 200SX SE that i took in for an emissions test today, which i failed. the diagnostic trouble code that was given is 

P0136 O2 sensor Circuit Malfunction (Bank 1(1) Sensor 2)
as written on my inspection report

which sensor is this and how can i fix this?


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## lshadoff (Nov 26, 2002)

That's the rear oxygen sensor. The sensor is in the exhaust pipe, near the first flange.

First, check the connector. Disconnect and re-connect it. See if the Check Engine light goes out after three driving cycles. (A driving cycle is starting the car, driving at least until it is fully warmed up, and then turning it off.)

If it doesn't reset on the fourth drive, replace the sensor.

After it is replaced, you should have the computer reset (at an auto parts store such as Auto Zone who does it free). This will clear any stored codes, but will unset the readiness tests. Depending on your state requirements, you may have to drive your car for a week or so to set the readiness tests, to pass emissions.

Lew


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## Marius (Jun 17, 2004)

lshadoff said:


> That's the rear oxygen sensor. The sensor is in the exhaust pipe, near the first flange.
> 
> First, check the connector. Disconnect and re-connect it. See if the Check Engine light goes out after three driving cycles. (A driving cycle is starting the car, driving at least until it is fully warmed up, and then turning it off.)
> 
> ...


could it also be the sensor that is near the converter? i have sensor that was welded on when i was running no cat conver.. now i have a converter thats welded after the sensor


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## Nostrodomas (Jun 15, 2002)

Well is the sensor welded into the pipe. Or is there a bung welde dinto the pipe and the sensor screwed into the bung?
It might be because the rear o2 sensor is supposed to be behind the under car cat. Or that if the sensor itself is welded into the pipe, it was damaged due to the extreme heat of the welding?


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## Marius (Jun 17, 2004)

the sensor is screwed in. are both the sensors the same or are they different (different part numbers). i might as well change them both, but not sure if they will be the same part.

where can i find out the part numbers for these O2 sensors?


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## Marius (Jun 17, 2004)

ok i checked a few things out. the rear O2 sensor is not welded straight to the pipe so i can screw it on and off, and it is after the converter. i took the sensor off the exhaust manifold, went to the auto parts and the guy wanted to know when my car was produced (the year) its a 1996, but how can i find out when it was produced? i checked on-line and for the 95-96 the bosch sensor is the same for those years

i re-installed the sensor and will drive with it for a few days and see if the ecu resets if not ill order that part off the net and replace it

any other sugesstions?

thanks


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## Nostrodomas (Jun 15, 2002)

If you look on the door jamb, you will see a sticker with a production date. If the car was made in month 5 or greater than the car will be the next year up. For example 7-1998, the car would be a 1999. If the date is 4-1995, then the car would be a 1995.
Have you been experiencing a loss of gas milage? That is the main symptom of a bad o2 sensor. 
So If the light does not come back on, I wouldn't worry about it. Unless you see a significant loss of MPG.


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## payk (May 5, 2004)

if the front and rear sensors are already a few years old i suggest replacing them cause they do wear out plus if you dont you can damage the cats by running too rich 
you have to drive it a lot too to reset the driving cycle partmaybe 20 miles or so


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## payk (May 5, 2004)

one more thing
you have to drive the car at least 30-40 mins 
at different speeds for the readiness test to be reset and ready


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## Nostrodomas (Jun 15, 2002)

Its actualy set up by trips. Turning the car on, driving it till its completly warm, then shut down. I believe this has to be done at least 3 times.


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## Marius (Jun 17, 2004)

does anyone know what size or part # the rear O2 sensor is on a 1996 200SX SE. i replaced the one on the manifold but i ordered the wrong one for the rear O2 sensor.

Any help let me know.

thanks


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## lshadoff (Nov 26, 2002)

Marius said:


> does anyone know what size or part # the rear O2 sensor is on a 1996 200SX SE. i replaced the one on the manifold but i ordered the wrong one for the rear O2 sensor.
> 
> Any help let me know.
> 
> thanks


According to Nissan FAST the part number is 226A0-40U61

Lew


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## Ninety-Nine SE-L (May 5, 2002)

I would hope the O2 sensor isn't welded into place, it needs to come off.

Anyway, I would assume all the O2 sensors are the same for the 96 and 97. The 95 GA16 is OBD1 and the 98-99 are usually different from previous models.

BTW, only the front O2 sensor affects fuel mileage. The front senses Oxygen in the exhaust fumes to determine lean/rich fuel mixture, the rear checks to make sure the cat is doing its job.


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## lshadoff (Nov 26, 2002)

Ninety-Nine SE-L said:


> BTW, only the front O2 sensor affects fuel mileage. The front senses Oxygen in the exhaust fumes to determine lean/rich fuel mixture, the rear checks to make sure the cat is doing its job.


That is true if the front O2 sensor is working normally. 

From the B14 FSM: 

"Even if the switching characteristics of the front heated oxygen sensor shift, the air-fuel ratio is controlled to stoichiometric by the signal from the rear heated oxygen sensor." 

The rear O2 sensor also plays the role of a back-up system in case the front O2 sensor fails. 

Lew


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## Marius (Jun 17, 2004)

thanks for all the help guys. i ordered the right O2 sensor and installed it. i also reset the computer. now im ready to re-test for emissions

one thing i dont understand is why the connector plug for the rear O2 sensor is under the carpet under the driver seat. made the work a little longer and i had to cut the carpet a few inches but its all done now

thanks


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## Marius (Jun 17, 2004)

ok im back. my engine light came back on. i reset the comp like 4 times already and i still get a rear O2 sensor code. how do i test the sensor to make sure its good?

another question is, how does the rear O2 sensor affect gas milage? i know the front O2 reads the air/fuel levels in the exhaust, but what does the rear one do, besides monitor the temp and stuff in the converter?


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