SadLambda

Hello
My car is civic vi D14Z2, year 2000

Self diagnostic code (blinking) is 63, which is second oxygen sesnor failure.
So my mechanic tried 3 lambdas already, first two were universal, I've told them that they should get dedicated for this model and I've found some on the web if they are interesed. They checked and said that one of them is ok and they've ordered it.

So, they replaced THIRD o2 sensor, check engine after 40 kilometers. Of course they charged money and said they have no clue what causes it, but "it works fine".

I did some research on my own and found out that P0139 code may be caused by " Front and rear HO2S connections reversed.". Guess what? The oxygen sensor they've ordered is front one (upstream) and they put it as rear one (downstream). They don't wanna give my money back for faulty part, because they insist that front and rear are exactly the same sensors and they are interchargeable - is it true?

It's hard to believe, because downstream costs two times more than upstream

ezone

Welcome to the forum!


We do not have any 1.4 over here (North America), and I have no access to repair info or specs for a car like that..... But here's my thoughts:


Your mechanic is broken, replace with a smarter unit.

In the USA, P0139 is defined as "rear O2 sensor slow response", which typically is due to a faulty sensor.


IF someone got the wiring swapped between the front and rear sensors, I suppose this code could be set. (I have not witnessed this situation before, but I can see how it could set if this were to happen.)

Next issue: The factory connector housings should have been different enough that the sensor plugs could not be swapped.
But I have seen some people go to a LOT of trouble to screw up something that should have been quite simple.

A correct OE wire diagram and very close inspection of wire colors at each sensor connection should reveal which should set of wires should be plugged in to what sensor, and where each sensor is supposed to be located (pre-cat or post-cat).

The cars do not like non-factory sensors, period.
The original sensors were probably made by NTK or DENSO, always replace using the same brand and type.


HTH

SadLambda

Hello again

Of course I have replaced my mechanic with smarter unit, as soon as I've realized that he won't fix anything which needs more than hitting it with hammer.

Sadly, the connectors for front and rear lambda are the same, thats why they managed to fit front into rear spot.

Original sensor was NGK(NTK) OHA 333-H25
They replaced it with NGK OZA 333-H4
According to this auction
http://www.ebay.ie/itm/NGK-NTK-Oxyge...-/140751852177
In section 'information' this sensor is FRONT one, but its compatible with 1.4 Civic (compability section)

I wonder if I can fight them to get my money back, because I gave them car to fix check engine, paid lot of cash to replace O2 sensor (which they believe was faulty - I'm more than 100% sure that they didnt check ANYTHING beside CEL code), yet I have SAME check engine...
Their last suggestion was to cut cat, because it may be faulty. Which I dont believe, correct me if I'm wrong, but if o2 sensor is ok (and they say so), broken cat would result in similar voltage output as front one, right? AFAIK it was stable at 0,45 V which would mean that cat is perfectly ok.

So, can the CEL be caused by wrong type of sensor? (front, instead of rear?)
Some people say that front one is exactly the same as rear one, but IMO they are different, they have different purposes so maybe they are built differently, for example they have different resistance or how fast they respond?

ezone

If the only tool in your box is a hammer, everything looks like a nail!



If you verify which set of wires is for front vs. rear, can you just swap the connectors and see if that solves the issue?

See if you can go directly to the NTK (NGK) website and look up your sensors there...
Is this it? http://www.ngkpartfinder.co.uk/

I do not normally trust ebay sellers.



Mechanic has both a hammer AND a saw?
The toolbox must be overflowing!


A bad (inefficient) cat will set its own code, in North America that code is P0420.
A clogged cat may or may not set a code, and a code does not mean the cat is plugged or restricted. The cat code only means its oxygen storage capacity has diminished beyond a predetermined cutpoint.

BUT the O2 sensors must pass their tests before the computer can run a cat test.
The cat testing will be suspended as long as there are O2 sensor related codes present.


If the cat is gutted or hollow, the rear sensor activity would mirror the action of the front sensor.
If it's still intact, the sensor activity would be less than the front.
If the cat is good, the rear sensor swing is much much slower than the front.


Assumed OK for the moment, watching sensor voltages is all you can do. \
You can guess and assume that the cat may be ok, but you can't actually judge if the cat is truly good by watching the sensors, The computer makes that decision for us when it runs its self tests as you drive.

But yes, your idea sounds correct.
I'm still thinking about that. Not sure now.....
if the connectors were swapped then the slow sensor would be the front one.
Rear sensor value as seen at the PCM would be very rapid voltage swings.

I know I see heater circuit codes commonly caused by incorrect sensors because they have different heater resistance values.

SadLambda

You mean swapping connectors at ECU so front becomes rear and vice versa? Well I'm not that skilled (yet) and wouldn't like to try on my own car, you know, learning on your own car is most expensive thing

Anyway, I've checked sensors at partfinder and...
http://www.ngkpartfinder.co.uk/car_c...e=1.4&pos=Rear
OZA 333-H25 is the only one listed as rear (code at original is OHA 333-H25, so I assume its exactly the same)

But if you check front sensor
http://www.ngkpartfinder.co.uk/car_c...=all&pos=Front
You can see that H4 is matched to my car but as front sensor.
If NGK differs those two, then I highly doubt they are exactly same sensors. They may differ in performance which is detected by engine and throws error code, right?

As far as I remember they said that second lambda thrown immediately lambda error and cat error, but they neglected it (correct me if I'm wrong, but codes are intermittent and persistent (?), and cat code can be intermittent)

IMO PCM expects correct performance from them, maybe the second one is supposed to "report" faster. Basically it seems that they are exactly same sensors, but there must be a reason why rear costs twice as much as front one and has no substitute.

ezone

Not at the PCM, I meant out at the sensor connectors (you said they use identical connectors).


I don't see a D14Z2 in the list, and the choice for D14Z1 shows a single wire sensor...Is that correct?
And the rear sensor link showed D14A engine?

I really don't have factory info for your version if the cars over there. Sorry.


I thought you said the sensors both have the same wiring connector shell.
The rear sensor uses 4 wires. Does your front sensor also use 4 wires? 5? 6 or more?

Is it an O2 sensor? A/F sensor? AFR sensor? LAF sensor?
Narrow band? Wide band?
The price goes higher as more letters are added to the name LOL



The rear sensor is normally a basic heated oxygen sensor, nothing super fancy. All it really has to do is report on the catalytic converter operation.



You said the mechanic can't figure out what's wrong with the car, so I would not trust whatever they told you as far as how it works.
Obviously, if they really knew how it all worked they could have fixed it right the first time...or at least told you what to expect.


The code P0139 was set when the PCM ran a test and the sensor failed. My info for this code basically says that the rear sensor output was observed to be incorrect at a time when the PCM forced changes in fuel delivery without seeing an appropriate response from the sensor in question (responded too slowly).



A single wire sensor can be very inexpensive, when compared to some other types.

According to the application chart, the rear sensor looked like it could be commonly used on many different vehicles.