[ExRaided]

Did some research and it could be as simple as the gas cap isn't tight with the check engine.That did nothing so I ran to auto zone and did a free test and got Error code F0420 Catalyst System Efficiency Below Threshold (Bank) 1.

Does anyone have any experience or knowledge with this? Is it anything major and is it covered by the warranty?

2018 impreza base BTW.

 

[Alex_Rochester]

I'm betting it's an O2 sensor. These are not the sort of things that a shadetree mechanic is likely to be able to fix. Unless you have a multimeter, there is no way for you to diagnose the problem.

 

[peaty]

I agree most likely an O2 sensor. How many miles on the car? I've seen this a lot in the past but usually with much older cars with a lot of miles. Typically the sensor behind the cat. It can happen if there is an exhaust leak.

It's true a loose gas cap can cause the code. In all the times that I've seen the code and checked the gas cap, only once it's been the gas cap. My kid misthreaded the cap and it felt tight but was cocked and not sealing.

 

[BruceP]

Why "guess" at this? .... simply read the trouble-code with a reader. Most auto-parts stores will read the code for free.

 

[Alex_Rochester]

He already got a reading. Read his post. Often they don't tell you much.

 

[ILuvMySubaru2]

BTW, the cruise control is simply blinking because the check engine light is on - any time a code sets, the cruise control is inactivated.

 

[DriftlessRider]

I get this generally on very cold days. But once I got it and did find the gas cap off

First thing I'd do is disconnect the battery for a few minutes to reset it. If it doesn't come back, I wouldn't worry about it.

Oh, wait. Yeah, if it's under warranty I'd let the dealer worry about it.

 

[peaty]

Sometimes it is related to the cold. The oxygen sensor after the catalytic converter is also looking for temperature I believe. That's why if you have a an exhaust leak or significantly change the flow with a different exhaust you can also get the code. I got it once and I went through such deep snow that it cooled the area down enough to make the sensor react. It went away next time I started the car.

 

[Steve L]

Did some research and it could be as simple as the gas cap isn't tight with the check engine.That did nothing so I ran to auto zone and did a free test and got Error code F0420 Catalyst System Efficiency Below Threshold (Bank) 1.

Does anyone have any experience or knowledge with this? Is it anything major and is it covered by the warranty?

2018 impreza base BTW.

YES, but it was on my 2005 RS2.5 and years ago so I dont remember now what it was. I cleared the alert using a obd2 scanner. memory has me thinking i had ignition faults, ie water on my wires which was throwing codes etc. only happened after I washed my engine bay etc. stopped after it dried out.

i would clear the code and drive it and see how it goes. Depending on if it returns, and how long it takes to return, could be helpful for the service department. Clear the code and drive it and see what happens. If its major, it'll return and also you may notice changes in engine idling and performance indicating an ongoing problem that needs looked at. Or, if it dissapears chalk it up to a misjujdged sensor voltage. (sun spots? Magnetic storms? Neutrinos?)

-s

 

[kastanko77]

Did some research and it could be as simple as the gas cap isn't tight with the check engine.That did nothing so I ran to auto zone and did a free test and got Error code F0420 Catalyst System Efficiency Below Threshold (Bank) 1.

Does anyone have any experience or knowledge with this? Is it anything major and is it covered by the warranty?

2018 impreza base BTW.

My code's been the worst case scenario I have an 07 legacy 2.5 l same condition I've already melted about 5 cats I've spent thousands and no one seems to know why it's dumping extra fuel ridiculous Also you know 02 sensors and everything in between's been replaced to be honest with you And if I reset the code while driving the car is fine all I have to do is re set the throttle body but it comes back between 50 and 200 miles

 

[AdaMoose]

Got this code yesterday. Took it into service today and just got a call. They are going to replace the cat.