Oxygen sensors

adriandilly

Hi,

This is my oxygen sensor data at 2000rpm, sensor 1 pre-cat and sensor 2 post -cat


Does anyone think my catalytic converter needs replacing?

I have a 2002 2.0l Ford Focus Ghia

Thanks

*j*

Deleted, didn't read the post properly!

*j*

rodenal

The precat looks fine in terms of switching although the voltage seems low - don't think it should be an issue given it's regularly showing on/off though. Post cat looks like it could have an issue, as far as i'm aware they should always switch between the same voltage so I would suspect the sensor rather than the cat - do you have an EML on? What's the code if so, also what car?

*edit sorry just re-read and seen the model*

Could be worth getting an emissions test done - the post cat sensor does nothing anyway so if emissions are high then change the cat, if they're normal then either change the post cat sensor or just live with the management light. Neither should be expensive for your car

Strider590

If anyone is wondering what that screenshot is from.....

It's the TORQUE app for android phones, it's connects your phone the cars ECU via bluetooth.

adriandilly

rodenal wrote: »

The precat looks fine in terms of switching although the voltage seems low - don't think it should be an issue given it's regularly showing on/off though. Post cat looks like it could have an issue, as far as i'm aware they should always switch between the same voltage so I would suspect the sensor rather than the cat - do you have an EML on? What's the code if so, also what car?

*edit sorry just re-read and seen the model*

Could be worth getting an emissions test done - the post cat sensor does nothing anyway so if emissions are high then change the cat, if they're normal then either change the post cat sensor or just live with the management light. Neither should be expensive for your car

I've posted on this forum before about this problem but I've only just received the bluetooth adaptor to look at the data (got lost in post). I've had EML on, once every week or two. I've been deleting it with a cheap reader, comes up with code P0420. I was under the impression the post - cat sensor shouldn't oscillate like the pre - cat; and because it is, the cat is shot?

rodenal

That's not my understanding though I'm far from an expert, as far as I know the voltage should constantly switch between a set voltage regardless of where the sensor is. This shows you that the sensor is working which is why I think the switching between .8 .6 and .7 on that second plot shows a problem with the sensor. On my mr2 the post cat sensor constantly switched between set voltages (after replacing a faulty one that didn't )
.


Emissions tedt should clear it up for you, if it comes out normal it'll be the lambda, if its high then cat

adriandilly

I've been trawling the net and getting conflicting answers.
Some sites say that post-cat sensors used to remain steady; but since 1999, oscillate like the pre-cat (efficiency thus taken by measuring lag from waveform 1 to waveform 2).
Other sites just say that post-cat sensors should not oscillate like the pre-cat (if they do, the cat converter is damaged).
I have however read that you should check for exhaust leaks, of which I believe my car has one. I'll get under there when the weather gets a bit warmer