P0420 Catalyst Efficiency below Threshold Bank 1

Per:

Catalyst System Efficiency Below Threshold (Bank 1) What does that mean?

Basically this means that the oxygen sensor downstream (after) the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system. Symptoms

You will likely not notice any drivability problems, although there may be symptoms. Causes

A code P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for * An oxygen sensor is not reading (functioning) properly * The engine coolant temperature sensor is not working properly * Damaged exhaust manifold / catalytic converter / exhaust pipe * Retarded spark timing

Possible Solutions

The simplest thing to do is to reset the code and see if it comes back.

Next step is to measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). The voltage should be low and steady (~200mV, depends on the vehicle). If the voltage varies (e.g. 100mV to 600mV) then it's time to replace the catalytic converter. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

Hey, Sounds like either an O2 sensor (or sensors) have gone bad or one or both of your Cats have gone bad. (Catalytic converter). Cats and O2 sensors both can be pricey. You should be able to price them both on-line, the parts at least. Neither are easy to replace by yourself w/o a lift, but it can be done.

I wrote the above before properly reading your email. If it's an after cat O2 sensor that is fairly easy to replace. Hopefully it's the O2 sensor and not the cat. Cats don't usually go bad in 5 years. Most are good for 20+ years.

It won't harm your car, not really. It might degrade performance a bit. Since they are part of the emissions system though, they should still be covered by 7 year emissions warranty. It is doubtful that you would pass any state emissions inspection.

I agree that resetting the code is a decent preliminary step. You'll need to disconnect the battery for about 15min.

If the code comes back, I would take the vehicle back to the dealer and see what they say. And research emissions warranties. I could be off on my figures, but 7 years seems to stick out in my memory.

Martin '01 Formula - MTI Air Box Lid, K&N Filter, Hurst-6, SLP Cold Air Induction & Smooth Intake Bellow Corsa Catback w/Premium Tips '83 V45 Magna

Actually I think its out to 10 years now. It depends on the age of the vehicle, but certainly his should be covered under the emmisions warranty. And at least in CA, the code having thrown would cause an automatic fail. You need to have a certain number of start-run cycles to even be eligible for smog check. As a matter of fact when we had to have to computer changed on our 96 Mitsubishi Galant (required by some recall that would not even let it be smogged until it was replaced) we had to wait like a week afterwards before they would let us get it tested.

Actually I think its out to 10 years now. It depends on the age of the vehicle, but certainly his should be covered under the emmisions warranty. And at least in CA, the code having thrown would cause an automatic fail. You need to have a certain number of start-run cycles to even be eligible for smog check. As a matter of fact when we had to have to computer changed on our 96 Mitsubishi Galant (required by some recall that would not even let it be smogged until it was replaced) we had to wait like a week afterwards before they would let us get it tested.

I went to Autozone and reset the code. It has not come back on today with about 10 miles of use.

I keep my fingers crossed.

Thanks for the help !