Let me ask my next question in the most direct way for my noob-ness under the hood of our S2000. Which harness is the one for the Primary O2 sensor?

Is there some kind of label, colour coding I can reference with?

Anyone with a dummy-proof picture to point me to it would be most appreciated

Just in case, mine is a MY07...

Thanks!

 

The primary 02 sensor is the one before the cat, and the seconday 02 sensor is the one that is connected to the cat.

Not sure if you can see it from the top but give it a try when the motor is cold.
From the passenger side fender, look at the motor and just below the red valve cover you would see an item with 4 arms that are connected to the motor.

That is the exhaust manifold. From there look down to where the manifold goes from 4 to 2 to 1. Where it is 1, the 02 sensold is mounted there.

I think you might have to look from under the car though.

Correction, yes you will have to look underneath the car.

 

Thanks for all the follow-up, SumAznGuy!

I do know how an exhaust manifold looks like at least I have seen them in pictures and diagrams before.

In that picture you posted, is that the primary O2 sensor that has been unplugged from the piping??

I thought you mention to unplug the wiring harness end (that feeds signal to the ECM) of the O2 sensor and clean up any bad contacts at that end... but now looks and sounds like you are suggesting to unplug the sensor end and clean the sensor? Is that what you mean?

The S being as low to the ground as it is, I assume to access it from underneath, the car needs to be jacked up? I don't have the equipment nor experience doing that, so sounds like a trip to a shop for me then =/

Please confirm my understanding. Thanks!

 

The unplugged one looks like the primary, aka a/f sensor. SumAznGuy is most likely suggesting you to check the connector side for corrosions etc.

How technical would you like to get? All you really need is a good dvom to check the heater circuits for resistance and shorts/opens.

 

Good job! I knew it would work! G/l fixing it, there are some great resources here!

 

Yes on all points.

In the photo, the unplugged sensor is the primary and the one in the back is the secondary 02 sensor.

If you follow the sensor, you will see a squarish shaped connector. See if it is properly plugged in. The car being an 02, I find it hard to believe the 02 sensor is dead, but I guess it could happen. Most 02 sensors that died on me, died around the 100K mark. But I guess YMMV.

 

[QUOTE=SumAznGuy,Jun 3 2009, 11:19 AM]Yes on all points.

In the photo, the unplugged sensor is the primary and the one in the back is the secondary 02 sensor.

If you follow the sensor, you will see a squarish shaped connector.

 

Hey guys, I had arranged with a shop to bring in the part (OEM is cheaper than generic, at least via his sources... I didn't try to eBay the part myself) and planning to bring the car in to replace the sensor.

Guess what though!?! This morning when I started the car, the CEL went off! I got to work, borrowed my coworker's scangauge again and the code is still in the "stored code" which is NOT a surprise.

I did not hit "clear" to clear the code because since there is nothing done to replace nor clean the sensor, I am not sure what to make of this at this point. I called the shop up to tell them what had happened, they suggest that the CEL will probably come back on eventually... well, I am planning to go to this shop to have my oil change done anyway (just hit 15% this morning at the end of my drive to work btw). So I cancel the next Monday appointment with them for now and told them I will drive the car like this for another week or so, when oil gets to 10% I will bring in to get oil change and have the sensor checked out / inspected and replaced if looks like it needs to.

What do you guys think of this?

Is it normal for the CEL to go off after a while?

I have driven about 200km since the CEL first came on. When the light was on, I was short shifting (usually @35000rpm but definitely <4000rpm) and no more than 1/3 throttle and the fuel consumption did NOT seem to go through the roof... not sure if it's because of my "easy driving" compensated an actually bad sensor or what... help please with your input.

 

If the CEL turned off, then the sensor is working. I would say keep driving and if the light comes back, then worry about it.

Hard to say for sure about fuel consumption with the CEL light on, but if the sensor was faulty, that will definately hurt the fuel consumption no matter how hard you drive. If the car is not getting accurate fuel readings, the ECU will automatically compensate by dumping more gas so the motor will not lean out. That is just how they are programed.

 

Thanks guys for all your feedback, especially SumAznGuy and Al in particular

I understand about how the ECU (or more specifically the ECM) is programmed to compensate the fuel mix when/if the sensor was faulty and not feeding back the air fuel ratio in the exhaust gas. The fact that the fuel consumption over the past ~200km I logged appears normal does point to me as well that the sensor is still working.

I will continue to drive the same normal way I always do, and see how it goes... I already VTEC and redlined once today since the light went off

Just still very very much wondering why the CEL came on with this code to begin with:
P0135 4 - 1 --------------- Primary Heated Oxygen Sensor Heater Circuit Malfunction (Sensor 1)

does this code mean the sensor ITSELF has malfunction OR ithe sensor's Heater Circuit has malfunction?