PO 420 catalyst efficiency belov threshold in Bank 1

[xdarkox]

Hi forumers,

I just while driving my mazda es 1.8 2000 got check engine light,went to autozone to read the code and its PO420.
i looked at mazda workshop manual and they don't have 420 code only 421 which is warm-up catalyst system efficiency below threshold.

I don't know where to start. I can visually check exhaust system for leakage ,but i don't know how one would check catalyst converter is it in good condition.
Im not even sure what is a Bank1 and where is located.
I just pass my emission test two weeks ago.
Can i drive my car like this,what is the downswing of driving it in that condition.

If anyone know anything about this pls let me know.


I got it fixed it was O2 sensor all along ,

[DeeAOne]

My girl's civic is throwing the same code. I know it's a civic but it's generally going to be because of the same issue. Check your o2s because they are cheaper to replace. If that doesn't solve it, you need a new cat.

I swapped out her stock cat for a Megan high flow, and it threw the code again. Going to change the primary o2 (wideband sensor) along with a defouler, and hope that does the trick.

Bank 1 is most likely your first o2 in the exhaust, the one closest to the engine.

At most, you will take a hit in the gas mileage catergory, but other than that it shouldn't have a huge effect.

[progt91]

your cat works but its not at its peek efficiancy. bank 1 is the o2 sensor closest to the engine. you can trip this code if you have an exhaust leak up front but more than likely its a cat issue. not a big deal to continue driving like this. obviouslt the cat was in good enough shape to give you an emissions pass. basically the pcm takes the reading from the first o2 and compares it to the reading coming from the second o2 and determines from there. to check the cat you could hook up a scan tool and look up datalogger paramiters. watch the readings from the first o2 should have a nice sweep up and down reading. second o2 should be pretty well flatlined. if the reading from the second o2 mimics the first (main o2) then that pretty much guarantees a bad cat.

[KAinjection]

^^^you posted while I was typing, haha


How to tell the location of the sensor is like this:
Bank 1 means---The sensor is located on the side where cylinder 1 is located, and on a four cylinder engine you will always get a Bank 1 code since there is no "Bank 2"
Bank 2 means---This only applies to V6-V8 type of engine with 2 banks of cylinders. Essentially its telling you the opposite side of the engine from Bank 1
Sometimes you will have a code say Bank 1 sensor 1, or Bank 1 sensor 2. This just means either before the catalyst or after it.
Sensor 1 is before the cat and Sensor 2 is after the cat.

Keep in mind that the rules above should apply to most any car, but there are always exceptions to the rule.

Dee is correct, you can get this code when the O2 sensors get bad. The best way to tell is to have a scanner that does a little more then read codes and monitor the sensor on a graph.

Sensor 1 (pre-cat) should be constantly switching from rich to lean fairly quickly and should react quickly to any changes made. Blip the throttle and you should see how it reacts.
Now remove a vacuum line from the engine and watch the voltage go down which indicates lean, then plug the line back in, and it will go rich momentarily (higher voltage).
Sensor 2 (after-cat) should be a little more steady and not switching as much. If the cat is working properly and the sensor is reading correctly, it will be reading lower voltage (lean). This sensor will react to the same test I mentioned for Sensor 1 but less dramatically.

This code can be happening from your engine not running efficient, cat not doing its job, or sensors that are lazy and reading incorrectly, although most of the time I find its the cat or sensors.
To answer your question, yes you can drive the car like this, it wont hurt anything, but if its the sensors causing the problem, it can be hurting gas mileage, power, and or drivability, so its really at your discretion what you want to do at this point.


Dee, if you replaced the cat with a new one and you still got the code, then more then likely its the sensors, and you should replace both of them.

[crazycanadian]

Easiest way to tell what it is for sure is with a proper scanner.... generic OBD data from generic scanners is to slow...

Good chance you need a cat.... O2 sensors can cause that code but with a proper scanner it takes no time at all to tell...

Sensor 2 (after-cat) should be a little more steady and not switching as much. If the cat is working properly and the sensor is reading correctly, it will be reading lower voltage (lean). This sensor will react to the same test I mentioned for Sensor 1 but less dramatically.

Dee, if you replaced the cat with a new one and you still got the code, then more then likely its the sensors, and you should replace both of them.

Post cat O2 should not switch at all like the Pre cat O2.... It will switch depending on what you are doing with the throttle, but at a steady state cruise it should sit pretty constant...

If Dee still got the code after a new cat he needs to be sure he got a proper converter.... There are a lot of cheep converters on the market that wont pass the factory catalyst efficiency tests...

[xdarkox]

very detailed informations ,I appreciate it a lot, Thanks

[DeeAOne]

Easiest way to tell what it is for sure is with a proper scanner.... generic OBD data from generic scanners is to slow...

Good chance you need a cat.... O2 sensors can cause that code but with a proper scanner it takes no time at all to tell...

Post cat O2 should not switch at all like the Pre cat O2.... It will switch depending on what you are doing with the throttle, but at a steady state cruise it should sit pretty constant...

If Dee still got the code after a new cat he needs to be sure he got a proper converter.... There are a lot of cheep converters on the market that wont pass the factory catalyst efficiency tests...

It's basically a test pipe with the same inside dimensions as the stock cat. No honeycomb inside, which is why it needs a defouler. The o2's would be destroyed otherwise. We don't have emissions here..

[KAinjection]

Post cat O2 should not switch at all like the Pre cat O2.... It will switch depending on what you are doing with the throttle, but at a steady state cruise it should sit pretty constant...

If Dee still got the code after a new cat he needs to be sure he got a proper converter.... There are a lot of cheep converters on the market that wont pass the factory catalyst efficiency tests...

yes which is why I said be a little more steady and not switching as much, and that it will react but less dramatically.

And yeah its possible the cat is not good quality, but not really that likely. A lot of cats get replaced in this area and 90% of the time they will get replaced with a cheap one that is welded into the exhaust, and not a OE replacement, but they always seem to pass.

Maybe they have different standards in Canada, Idk

[goldstar]

progt91 and 300zxrb26dett, a very detailed, informative explanation of the problem that should be of great help to our Forum members. Thanks for posting.

Happy Motoring!

[xdarkox]

I just looked over some O2 sensors and most of them they sell are 4 wire,mine 02 sensor are 3 wire, the ones with 3 wire are sold without a connector,and most of them with 4 wire have connectors already instaled.
Am i going to be able to hookup 4 wire sensors.

[KAinjection]

If you cant find the right one, then try searching for a year earlier or a year later then your model year, sometimes if the production date falls close to another model year it will be different, or it could even be the difference between a California (50 state) emission model and a Federal (49) state emission model. Its really honestly better if you can find the correct one with the connector. The ones without the connector are the universal ones and have to be spliced in, but that would have to be a last resort.

[xdarkox]

O2 sensor all along ,nothing to do with CAT ,quite happy about it