Would my car pass emissions straight after having my cat replaced? (Code p0420)

My car’s engine is burning oil. This damaged my current catalytic converter and is bringing up code p0420. I won’t be able to pass emissions inspection at this time.

If I replace the cat and immediately go for an inspection, do you think the car will pass? Or does the car have to be driven for a certain amount of miles first?

Thank you

If the Check Engine light is off during the test, the vehicle will pass.

If it’s on, it will fail.


1 Like

Thank you.

If that was always the case though, couldn’t I just clear the P0420 code and have the CEL temporarily off with a bad cat? I was told that the vehicle would still fail under these conditions.

1 Like

If you clear the code before having the vehicle tested, the readiness monitors have to be reset.

So, if the readiness monitors haven’t been reset, you’ll fail the test.



Do you know how to reset the readiness monitors on a '05 Camry?



I’m going to experiment with getting the monitors ready. A Texas state website says:

" For vehicles year model 2001 and newer, we allow one (1) non-continuous monitor to be [“Not Ready”] and still pass the test."

Do you know what is meant by “non-continuous?”

That means a monitor that’s ongoing. but not ready/


1 Like

Monitors that are performed once per drive cycle; Catalyst monitor, Evaporative emissions monitor, Oxygen sensor heater, EGR monitor etc. These are the monitors that must be completed for an emissions inspection.

An example of a continuous monitor is the misfire monitor, this is always running.

1 Like

I cleared my P0420 code and tried a recommeded drive cycle I found online. I was able to get the Oxygen sensor monitor ready, but not the Evap or Catalyst. I didn’t see EGR listed. Do you know why this is?

I was trying to get the Catalyst monitor ready by driving 55-65 mph for 15 minutes. Shortly after this, my CEL light came back on. Do you know if my CEL came back on as a direct consequence of my Catalyst monitor becoming ready?

I’m guessing that I may have to to get the oxygen sensor and evap monitors ready and leave the catalyst monitor alone. In the state of Texas, a car can pass inspection with one unready monitor.

here’s my recommendation . . .

Today, make sure you have a 1/2-tank of gas

Tomorrow morning, start the car cold, drive 10 minutes on city streets at a reasonable speed . . . not racing from stoplight to stoplight . . . then drive another 15 minutes on the freeway at a steady speed and hopefully you’ll get them all

A word of caution . . . in many states, that incomplete readiness monitor may NOT be catalyst

So don’t freak out if you show up with all complete EXCEPT catalyst and they give you grief

1 Like

The Texas state website says they allow one monitor to not be ready. It doesnt say anything specific about catalyst, so hopefully I’ll be fine.

Thanks for the tips. My plan is to get the EVAP ready and then head for inspection with the Catalyst not ready.

Have you heard anything about a car having to be in 40° temperature or above overnight for the EVAP to come on?

There are some cars where the evap monitor will not run with extreme ambient temperatures one way or the other . . . meaning too hot or too cold and you’re of luck

Good luck . . . I think you’ll be fine! :+1:

1 Like

Thanks. I will try your method of 10 minutes of city driving today.

I just tried driving to 60mph and allowing the car to slow down by itself. I heard about this method from a youtube video for getting the evap system ready. Unfortunately, this made my catalyst system ready and turned my CEL back on.

I have to figure out how to get my EVAP system ready without activating the catalyst.

This is the first car I’ve ever owned and I really don’t want to have to get rid of it.

Sorry you are having this difficulty @nickc498 . There’s another Texas poster here who has been keeping us up to date with his own evap monitor problem over the past few months, so you might want to check those threads out. Chrysler/ Dodge Caravan as I recall. You can use the forum search feature to find them, link upper right this page. Texas apparently allows a car to pass after spending a certain amount of $$, $-exemption limit, which is how that poster finally got his registration renewed. Shop was unable to resolve problem in time.

If only problem is cat, seems like a pretty good chance a new cat will allow your car to pass. Might not work if mixture is way too rich though. If don’t know, ask your shop do a fuel trim test. Good idea anyway, b/c if mixture too rich, new cat may be quickly damaged. If you have an evap problem too, that might prove more problematic. Evap problems can be like finding a leak in a swimming pool, can take quite a bit of investigation. But as a back-up you have the Texas $$-limit exemption.

How much oil is your car burning? Quarts per 1000 miles. Are you sure it is being burned and not just leaking out onto the ground?

Thank you for your input. I will check out the thread.

I tried getting the Texas exemption. The state requirement is you have to spend $600 or more in repairs related to the problem that is creating the CEL. The auto shop was only able to bring repair costs up to about $500.

I know that the engine is burning oil because I’m losing more than a quart every thousand miles without any significant leaks. I was told that a new cat will likely be damaged shortly after installation.

I just saw a Scotty Kilmer video where he recommends using a gallon of fuel injector cleaner and driving on the highway for 30-45 minutes. He said he’s been able to get hundreds of vehicles to pass emissions that way.

That thread on the Dodge Grand Caravan was a real disaster, the owner was given the runaround for several week over a evaporative emission system leak diagnosis. The vehicle never passed; the owner obtained a low milage waiver for one year.

The engine in my 2000 Dodge consumes one quart of oil every 750 miles, there is no problem with my catalytic convertor. Was a cheap, inferior catalytic convertor installed on your car? Was the function of the oxygen sensors verified? Inspected for exhaust leaks near the engine and catalytic convertor?

1 Like

I don’t have any codes coming up for the oxygen sensors, and the mechanic didn’t mention anything to me about exhaust leaks.

It’s possible that the catalytic converter is cheap and inferior. It’s a Dorman that I bought from Rock Auto for $314 three years ago.

Dorman should be a trusted product. The Dorman front catalyst is now $700, are you sure that is what you bought?

A failing downstream oxygen sensor won’t always set a fault code for the sensor, but the computer can set a catalyst efficiency fault.

Your mechanic didn’t mention an exhaust leak, but did he look for one? With all the work that has been performed on this car, a small leak at one of the exhaust system joints is a possibility.

1 Like

Yes, I was actually surprised to see that the Dorman has jumped up to $700. The product number is 6738111. I still have the email receipt.

I’m not sure if the mechanic checked for exhaust system leaks. I just had him diagnose the cause of the check engine light last week. He said the cause is the cat.

I should’ve told him to look at a possible exhaust leak because I do see a drop of fluid every morning that is coming from the front passenger side of the car. It could be from the engine or it could be the power steering fluid. I’m frequently losing power steering fluid, so I know there is a leak somewhere.