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Discussion Starter · #1 ·
Hello all!

I have a 2014 Focus SE 2.0 Flex that has a very stubborn P0420 code causing CEL and inability to pass emissions. I have had this code off and on for the last few years and it goes on and off but I have now moved to a new state requiring emissions testing and need to get this sorted out. So far, I have replaced the upstream and downstream O2 sensors, replaced the cat (https://rb.gy/mfdjxs), replaced the EVAP purge valve, cleaned the MAF, ran a can of STP intake valve cleaner, and tried many fuel additives (trying Techron next fill-up). I recently bought a OBD scanner and was able to pull the freeze-frame of when the code was set in that is attached below. Really hoping to get any possible solutions as this has been really bugging me for quite a while now!

Thanks!
311242
311243
 

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Hello all!

I have a 2014 Focus SE 2.0 Flex that has a very stubborn P0420 code causing CEL and inability to pass emissions. I have had this code off and on for the last few years and it goes on and off but I have now moved to a new state requiring emissions testing and need to get this sorted out. So far, I have replaced the upstream and downstream O2 sensors, replaced the cat (https://rb.gy/mfdjxs), replaced the EVAP purge valve, cleaned the MAF, ran a can of STP intake valve cleaner, and tried many fuel additives (trying Techron next fill-up). I recently bought a OBD scanner and was able to pull the freeze-frame of when the code was set in that is attached below. Really hoping to get any possible solutions as this has been really bugging me for quite a while now!

Thanks!
View attachment 311242 View attachment 311243
Well, it was hot as crap outside and you're running E15 or really poor E30 fuel. I think lol.
I solved my p0420 with a "J" style defouler, however I installed a high-flow cat that made this necessary.
If you don't think the emissions nazis where you live will see the defouler, I'd go ahead and slap one of those one to rule out the cat and the sensor totally.
Have you checked the wiring in the are to make sure nothing is melted/frayed?

I'm not super versed in the 2.0flex so maybe someone else can chime in?
 
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The P0420 typically registers when the oxygen sensors in front and behind the converter are reporting readings that are too similar. This is usually because of a bad cat.
Possible P0420 causes:
-damaged or failed downstream(rear) O2 sensor
-downstream O2 sensor wiring damaged or bad connector/plug
-engine coolant temperature sensor is not working properly
-damaged or leaking exhaust manifold, catalytic converter, or cat pipe
-failed or underperforming catalytic converter
-bad fuel quality
-oil contamination to cat

Some of these causes will also usually mean other codes are registered at the same time but not always:
-retarded spark timing
-cylinder misfire
-leaking fuel injector or high fuel pressure
-no spark from a bad plug or faulty coil/wiring
-clogged air filter or obstructed airbox(debris like leaves)
-air intake leaks
Since you have only the P0420 code I would bet that the cat is no good as my primary guess or the O2 sensor is no good as my secondary guess.
Your choice of fuel or where you buy it from may also be the issue. If it's not a top tier gas station I always pass it by. Most but not all top tier stations are legacy name brand. For instance Gulf is not. A couple of generic type brands actually are top tier like Costco and Valero. TOP TIER™ Gasoline Brands (toptiergas.com)
 

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Since you have only the P0420 code I would bet that the cat is no good as my primary guess or the O2 sensor is no good as my secondary guess.
Op already replaced both. What's your bet they got some defective parts? Lol

I'd think fuel could play into that too.
Does top tier rank gas stations based on their ethanol as well?
His E content was E18. That's either a really stiff fill up of E15, a really weak fill up of E30, or some miscalculation when mixing E85.

If the OP is mixing E85 are they mixing with 87, 91, or 93?
 

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Op already replaced both. What's your bet they got some defective parts? Lol

I'd think fuel could play into that too.
Does top tier rank gas stations based on their ethanol as well?
His E content was E18. That's either a really stiff fill up of E15, a really weak fill up of E30, or some miscalculation when mixing E85.

If the OP is mixing E85 are they mixing with 87, 91, or 93?
Yeah, I missed that lol.
It could be. Also, aftermarket cats are known to not always do quite the same job that factory cats do. With prices of rare earth metals right now I wouldn't be surprised if an aftermarket brand skimped. If there was no change after replacing any of the mentioned parts then I'm thinking it's something else though. He really needs to get live data and look at the upstream and downstream sensor readings. Sensor 1 should fluctuate and sensor 2 should be pretty steady.

Top Tier just means they meet certain minimum standards of detergents, stabilizers, additives, etc. for cleaner quality gas. As far as I know ethanol plays no part in how they meet that criteria since almost all gas in the country has a certain amount of it in there unfortunately.

If he's alternating between different ethanol content gas tank refills then it will give an uneven %. The stuff in the tank will mix with whatever he's putting in next.
 

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Discussion Starter · #6 ·
Op already replaced both. What's your bet they got some defective parts? Lol

I'd think fuel could play into that too.
Does top tier rank gas stations based on their ethanol as well?
His E content was E18. That's either a really stiff fill up of E15, a really weak fill up of E30, or some miscalculation when mixing E85.

If the OP is mixing E85 are they mixing with 87, 91, or 93?
I have been running 87 since replacing all the parts in the OP. Just recently filled up with 93 to try and fix that ethanol content and even got that metric reset at a local shop (for $40) in hopes the car would correct itself, but it definitely has not.
Took it to the dealer to see if they could reset the PCM, but they said it was on the “latest version” so they couldn’t do anything. Still at a loss for why this is happening.
 

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Discussion Starter · #7 ·
Yeah, I missed that lol.
It could be. Also, aftermarket cats are known to not always do quite the same job that factory cats do. With prices of rare earth metals right now I wouldn't be surprised if an aftermarket brand skimped. If there was no change after replacing any of the mentioned parts then I'm thinking it's something else though. He really needs to get live data and look at the upstream and downstream sensor readings. Sensor 1 should fluctuate and sensor 2 should be pretty steady.

Top Tier just means they meet certain minimum standards of detergents, stabilizers, additives, etc. for cleaner quality gas. As far as I know ethanol plays no part in how they meet that criteria since almost all gas in the country has a certain amount of it in there unfortunately.

If he's alternating between different ethanol content gas tank refills then it will give an uneven %. The stuff in the tank will mix with whatever he's putting in next.
I’m seeing lots of fluxing on the downstream 02. The upstream is a wideband sensor so it’s shown in mA with very minimal fluctuation. Also, as I replied earlier, I have been running 87 the entire time except for recently when I got 93 to try and sort out this issue.
 

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87 or 93 octane in your car doesn't matter and that's not what differentiates a cheap gas from Top Tier gas. The brand of gas is what's relevant as only certain brands(all octane grades usually included) make the Top Tier designation. Click on the link I provided to understand what it is.
No, the upstream sensor should be fluctuating and the downstream should be relatively steady.
Check the live data on a good scanner to see the front and read O2 sensor signals. The car engine should be warmed up completely and the front sensor should fluctuate between 0-1 volts, and the rear should be steady at 0.7 – 0.9 volt. There should also be a drastic difference in temperature from the front to the rear of the cat. If either of these are not the case then more than likely the catalytic converter is defective.
 

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Discussion Starter · #9 ·
87 or 93 octane in your car doesn't matter and that's not what differentiates a cheap gas from Top Tier gas. The brand of gas is what's relevant as only certain brands(all octane grades usually included) make the Top Tier designation. Click on the link I provided to understand what it is.
No, the upstream sensor should be fluctuating and the downstream should be relatively steady.
Check the live data on a good scanner to see the front and read O2 sensor signals. The car engine should be warmed up completely and the front sensor should fluctuate between 0-1 volts, and the rear should be steady at 0.7 – 0.9 volt. There should also be a drastic difference in temperature from the front to the rear of the cat. If either of these are not the case then more than likely the catalytic converter is defective.
So is the upstream sensor not supposed to be a wideband? I also can’t see the upstream vs downstream temps, only downstream.

I read the live data and the upstream (wideband) is fluctuates wildly (-.48mA to 2.3 mA) and the downstream also goes crazy (.12V to .8V)
 

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So is the upstream sensor not supposed to be a wideband? I also can’t see the upstream vs downstream temps, only downstream.

I read the live data and the upstream (wideband) is fluctuates wildly (-.48mA to 2.3 mA) and the downstream also goes crazy (.12V to .8V)
You can get an infrared temperature check gun to get the temps on the front/back of the cat.
.12v-.8v is too much fluctuation though. That's double the .2v amount that's typically seen. Your cat is most certainly defective and ineffective.
 

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Just chiming in to say that I also have this issue. I haven't tried anything to fix it yet but it will clear after long highway drives and if I can time it just right that's when I get the emissions checked and passed while the light is off the next day after the long drive.

I'm dreading this not working at some point and needing to replace the cat. Seeing above that the cat replacement didn't work is not encouraging :(
 

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Just chiming in to say that I also have this issue. I haven't tried anything to fix it yet but it will clear after long highway drives and if I can time it just right that's when I get the emissions checked and passed while the light is off the next day after the long drive.

I'm dreading this not working at some point and needing to replace the cat. Seeing above that the cat replacement didn't work is not encouraging :(
He replaced his with a VERY inexpensive aftermarket cat/manifold assy. Aftermarket cars are known to cause problems right out of the box so to speak. Do the test that I outlined above in #8 an #10 and that will give you a fairly definitive answer whether the cat is the problem or not.
 
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