CEL but emissions readiness all green

[calvin1]

I have a 2000 Subaru Forester that I need to get emissions tested. It has a p0420 code. I replaced the O2 sensor but the code came back. I'm hoping not to need a new catalytic converter if I can help it. The weird thing is all the emissions readiness checks show green even though I have a check engine light.

Anyone ever seen where you have check engine light but all the emissions tests are passing? I'm trying to figure out what this car is trying to tell me.

 

[Astro14]

I have a 2000 Subaru Forester that I need to get emissions tested. It has a p0420 code. I replaced the O2 sensor but the code came back. I'm hoping not to need a new catalytic converter if I can help it. The weird thing is all the emissions readiness checks show green even though I have a check engine light.

Anyone ever seen where you have check engine light but all the emissions tests are passing? I'm trying to figure out what this car is trying to tell me.

The car is trying to tell you to get a new catalytic converter.

The code is a catalyst system, efficiency warning. The ECM is comparing values between the upstream O2 sensor, and the downstream O2 sensor.

Those values are out of range against each other because the catalytic converter isn’t working that well anymore.

Some people have had luck by putting a “spark plug spacer“ on the downstream O2 sensor…. It changes the reading on that downstream one, and the ECM thinks the cat is working better as a result. I don’t know the rules in your state, and I’m not suggesting this is legal, I’m just describing how the system works.

 

[21_6.7f450]

It's probably on the verge of failing of the cat. Put a bottle of Redline SI-1 in an empty tank, fill it up and run it in a lower gear and get the rpms between 4k-5k will several full throttle runs from 40-80mph for 30 minutes. A failing cat can get hot and still pass.
Does it burn oil

 

[Mechanician]

Readiness test for the cat must have passed at least the first time it ran, since the last time you cleared the DTC.
The readiness codes remain until you clear the DTC.

 

[DriveHard]

sounds like the Cat isn't working properly. You could try spacing the second O2 sensor out of the stream with a spacer...

 

[Donald]

24 year old car. How much is a new cat?

 

[21_6.7f450]

I'd try what I suggested before a new cat.

 

[calvin1]

24 year old car. How much is a new cat?

AutoZone shows a universal for $200. IDK what labor is for the cut and weld. Maybe $750 all in?

 

[JavierH19]

If Indiana doesn't require emissions after 25 years honestly I'd just drive it expired for a year until it's exempt then get it inspected. I'd try a spacer and maybe cleaning the cat but it's not worth putting one in, especially since it may not need to pass emissions soon anyway.

 

[JavierH19]

AutoZone shows a universal for $200. IDK what labor is for the cut and weld. Maybe $750 all in?

How does the emissions exemption law work over there in indiana. The car is at most a year from being 25 years old though I don't know if the law goes off of month and year or just the year the vehicle is manufactured or the model year it's sold as being a 2000 for you.

The car is likely made in 1999 and could just be months away from being exempt if it does go by month and year manufactured but i don't know that for sure. Check to see what the date is on it and I'm guessing you checked emissions yourself with an obd reader before taking it to some inspection place to prevent wasted time but maybe try it anyway and go ask what they say about the exemption. I do remember having the cel on but i still passed inspection because all those things passed. But i have had the cel off once and it didn't pass because one of those things was listed as not ready. Go to the inspection place anyway.

 

[calvin1]

How does the emissions exemption law work over there in indiana. The car is at most a year from being 25 years old though I don't know if the law goes off of month and year or just the year the vehicle is manufactured or the model year it's sold as being a 2000 for you.

The car is likely made in 1999 and could just be months away from being exempt if it does go by month and year manufactured but i don't know that for sure. Check to see what the date is on it and I'm guessing you checked emissions yourself with an obd reader before taking it to some inspection place to prevent wasted time but maybe try it anyway and go ask what they say about the exemption. I do remember having the cel on but i still passed inspection because all those things passed. But i have had the cel off once and it didn't pass because one of those things was listed as not ready. Go to the inspection place anyway.

There's no exemption for age here (1975 or later), even pre OBD2 have to run on the rollers.

 

[SubieRubyRoo]

If Indiana doesn't require emissions after 25 years honestly I'd just drive it expired for a year until it's exempt then get it inspected. I'd try a spacer and maybe cleaning the cat but it's not worth putting one in, especially since it may not need to pass emissions soon anyway.

Only Lake & Porter counties have emissions testing in Indiana. Ignore the light and drive on if you’re not in those two counties

 

[Donald]

Only Lake & Porter counties have emissions testing in Indiana. Ignore the light and drive on if you’re not in those two counties

A small piece of duct tape over the CEL light.

 

[atikovi]

AutoZone shows a universal for $200. IDK what labor is for the cut and weld. Maybe $750 all in?

Doesn't take 5 hours to cut out and weld in a new converter. Maybe 1/2 hour to one hour max for someone that's experienced at it.

 

[Nukeman7]

I'd try this product to see if it removes some of the carbon build-up from the catalytic converter before installing the spacer on the downstream oxygen sensor.

Cataclean

 

[ArrestMeRedZ]

I don't know if this will work for your case, but I've seen it work on other codes set. It works on the principle monitors can pass before a failure code shows up with a DTC and CEL.
If you have a code reader, clear your DTCs. Then do a drive cycle and check your monitors. If they aren't all set, you may need another drive cycle or two (Evap is the one that doesn't need to be set most states). Once all (except Evap) are set, get it smogged right away.
Good luck!

 

[BrendanC]

dig a 1/2” bit through a spark plug antifouler and install. i go straight to two of them and that has “fixed” both accords

 

[Cujet]

There are also O2 sensor spacers with built in cats. They sometimes work to prevent a CEL. Quality varies here, AliExpress is one option. I've seen quality versions used in the very high-end car world for competition cars.

Sometimes, cats can be cleaned by immersing in a near boiling solution of citric acid for a few hours.
Costs about $5. Youtube can help here.

Also, the downstream O2 sensor can fail or be slow to respond. The downstream O2 sensors are generally considered more reliable as they operate in a less harsh environment. Some are heated, and that can fail too.

 

[repairman54]

A small piece of duct tape over the CEL light.

Black electrical tape is less noticeable.