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code P0420 I dont understand

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RyyanBell

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Discussion starter · #1 ·
P0420 catalyst system efficiency is below threshold (bank 1)

Im guessing this mean the chemical reaction in the catalytic is not reacting efficiently lol.

My friend thinks its just an 02 sensor.

Anyone able to shed some light on this for me?
 
#3 ·
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Indicates Bank 1 catalyst system efficiency is below the acceptable threshold Use of leaded fuel
Damaged HO2S
Malfunctioning ECT
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires improperly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Compare HO2S upstream and downstream switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.
 
#5 ·
Could be from running very rich, the cat is bad or the sensor is bad. All it really means is that you are polluting more than the computer would like you to.

I'd clear the code and see if it comes back (may take a few drive cycles). If it does see if there is also a slow HOS2 response code (sure bet an O2 is bad).


How many miles are on the car and do you know the maintenance history of it?
 
#6 · (Edited)
It could just be the sensor. Sometimes cats can just fail, but usually there is something else wrong that causes it to fail. ie running rich etc...

With a scan tool that can read PIDs, watch the two o2 sensors. The front o2 should have an up, and down wave form. The rear should be a flat line, if the cat is working correctly.

Edit: Oops, I'm late.
 
#8 ·
> if you have a bad 02 sensor and let it go for too long it will take out the cat also..

True if it is the O2 sensor in front of the cat, but the O2 sensor after the cat is only used for monitoring the cat operation, and it's the post-cat sensor you're looking at in a P0420.
 
Discussion starter · #11 ·
so its basically a 90% chance thats its an 02 sensor after the cat? So basically its not absolutely imperative that I get it fixed right now...Im planning a trip to the states soon and I don't have a lot of money, and Id like to spend it on that. Basically what I would like to know is am I running a high risk of breaking down? Or could I potentially leave it for awhile?

the car has 183,000 KM....112-113ish miles. I have no Idea about the maint. history.
 
#14 ·
mine pops off and on at random. every time its the same code. and it depends on the gas station as well. sometiles it'll be on for a 1/4 tank and trun off, sometimes it wont come on at all for the entire tank. aometimes it pops on when the tank get to the 1/4 left mark. and this is the same grade gas at the same station every time. so what gives with this?
 
Discussion starter · #16 ·
Hey Grumpy :)
I am actually in Surrey and when I bought the car in April it had passed air care no problem and is aircared until february 2010. I haven't had the car very long and don't know much of the history of it.
 
#17 ·
The ZTS had a Zetec or a SPI? It isn't going to quit on you.....take your trip and troubleshoot it later. The rear O2 sensor is not normally used by the ECM except as a precat/cat monitor. Have you done anything to the car recently (since AirCare)? Check for intake ducting air leaks downstream of the MAF, and listen/check for vacuum leaks. Exhaust tight and intact? Any sign of even a hint of a misfire at any time? As you don't know much about the car's history have you checked/replaced the spark plugs, checked the ignition leads etc.? Any sign of hunting/surging at 100 kph on the highway? If in doubt......change the fuel filter. Even a good precat/cat can only handle so much O2, so what you are looking for is the possible cause of the excessive O2 that may be getting to the precat/cat. Anything that can cause a lean mixture can aggravate this. If the car has EGR, not enough/no EGR is another thing that can cause this. Check the above stuff first before just assuming it's caused by a duff cat and/or the rear O2 sensor.
 
Discussion starter · #18 ·
wow, thats a lot to go through.
Its a Zetec.
I replaced the timing belt, the engine coilpack (not the sparkplugs) Doesnt misfire totally fine. I dont know what you mean by hunting/surging but it shakes alot accelerating over 100 km. Im getting an oil/air/fuel filter change next week lol

Whats EGR?
 
#19 ·
You mean the shaking starts when you "tromp on it" and accelerate and then the shaking stops after you stop accelerating, or is the shaking more like maybe a wheel balance issue anytime that you go above a 100? If the shaking occurs when you put a good load on the engine like accelerating in a higher gear, that sounds like it could be missing. Exhaust Gas Recirculation is used under some engine operating conditions to control NOx emissions. Exhaust gases are metered into the intake manifold which displaces/replaces some intake air (and the O2 in that air) to slightly enrichen the mixture and keep the combustion temp low enough to control NOx (high combustion temps can increase NOx emissions). I believe the SVT Zetec (has variable valve timing which deletes EGR) is the only engine of your year that doesn't have EGR.......so your EGR is something that may need to be looked at. There are other people on this forum that can answer any detailed questions on the Focus EGR system. I've only dealt with the full digital EGR systems used on other cars. I'm not sure if the Focus system is "tested" at any time and when tested if it doesn't actually deliver exhaust when it should, if that is detectable by the ECM and if the ECM will set a code.
 
Discussion starter · #20 ·
It shakes only while im accelerating over 100 kph, and even if im going say 130 as long as im not accelerating its smooth. I don;t really see what this has to do with emissions but ok. But basically look at the 02 sensors, and the EGR? But im not risking any engine damage or b reakdown if I wait a couple weeks? I don't drive a whole lot other than my planned trip to seattle and even then its only a 3 hour drive. I do have a AAA membership but its something Id rather not deal with.
 
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RyyanBell
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