SES light question

[ryan8795]

I had an SES light on and a diagnosis performed and was basically told that my bank 2 cat was plugged, hence the SES light. So, i'm just wondering how the SES light works; if the cat is cleaned and then started performing to reduce the emissions to be within specs, would the SES light go out on its own? Or do you have to get the code cleared and see if it comes back on?

After diagnosis, the code was cleared, after driving a few days later, it randomly pinged back on. I then disconnected neg battery terminal to turn SES light off. A few days it's back on again and remains on.

So i'm just wondering how it works. e.g. does one 'bad reading' trigger the error and the light remains on regardless of whether readings after this are not erroneous. Or does the fact that it's on mean that the cat is continuously not working as it should.

Hope that makes sense
Thanks

 

[AppleWood]

Don't think you can "clean" the catalytic converter. It gets plugged up over time and needs to be replaced. https://www.youtube.com/watch?v=VbDlSNYC7tM

One caveat is a defective O2 sensor causing SES light to come on.
https://www.yourmechanic.com/services/oxygen-sensor-replacement

 

[ryan8795]

Thanks. I guess I meant more hypothetically, if the cat happened to become un blocked etc, would the light go out, or would it remain on.

I'm confused as to what the problem is on mine as I spoke to a guy at Ford and he said if it's a bad cat the engine light would be flashing. Mine isn't, it's just on constantly. Just wondering if this can still be a bad cat or would it more likely be a sensor. Fuel economy seems ok, and haven't noticed any loss of power

 

[AppleWood]

You're welcome Ryan! And you piqued my interest in this as well.

So, here's interesting info about the sensor. As I understand it, if the percent oxygen in the exhaust stream goes back into the "normal" range, eventually the SES light should go out. But, this let's us know what the sensor is looking for as well.

http://www.obdii.com/articles/Understanding_Oxygen_Sensors.html

 

[lincolnshibuya]

a bad cat (not a plugged one) just means an an emission control issue, you can still drive while the SES is on. The only thing you're doing here is polluting the environment.

one of the reason why a cat failed is due to misfires, this issue needs to be addressed first because a new cat will get destroyed again.

if the cat is fine, then the 02 sensor is busted and needs to be replaced, there's 4 of them. The 2 primary ones (pre-cat) are important (they control your fuel trim) and 2 secondary ones (post cat) are just for monitoring purposes and not a big issue in terms of drivability.

AFAIK the Ford SES light will turn on/off if the test passed/fail, it's not like Mercedes where you have to use their special tool to reset the codes.

try going to a parts store have them scan for codes and post it here.

 

[ryan8795]

http://www.obdii.com/articles/Understanding_Oxygen_Sensors.html

Interesting read, thanks for the link, it sure did clarify a few things. I'm not sure what voltage the post-cat sensor should read, or how it behaves though. I got mine diagnosed and i'm pretty sure it was code P0430. Apparently the mechanic did some tests which showed the pre-cat sensor was oscillating between the two voltages correctly, and told me the cat was plugged.

If I disconnect the negative battery terminal to get the light off (which I have done twice so far), the light doesn't come back on straight away. This is where i'm confused. I've driven about 400-500km's without the light coming back on (highway and urban). Other times it could come back after 30km's or so. But once it's on, it remains on permanently.

Does this indicate a plugged cat as the mechanic said, or if not i'm wondering if the post-cat sensor could be the culprit. Saying that, i'm unsure how the post-cat sensor would prompt the SES light if it isn't talking to the ECU (or is it?).

 

[lincolnshibuya]

My friend's 2006 suzuki forenza does that, we clear the codes and after a week of driving it goes back P0420 (bank 1) clearly indicates that the cat is bad.

 

[ryan8795]

Ok thanks, good to know.

I'm also wondering what taking the cat out will do. I have herd mixed opinions...if I smashed out the material so it was open, would this result in a SES light on permanently? Or would it prevent the light coming on.
I guess I'm wondering whether it's the post cat sensor that is actually sending signals to turn the SES light on. Surely the pre-cat sensor wouldn't know the difference. Not sure if it's something to do with over heating, due to the plugged cat, that turns the light on either. If anyone can shed any light on how these components communicat, that would great