I was driving my car home and my CEL light turned on. I was about 2 miles from my home and I listened to the car to see if there was any funny noises or something out of the ordinary happening. The engine seemed to be running fine and the acceleration didn't seem to change either. I took the car to autozone the following morning and it threw a p0420 code. They said it had something to do with my catalytic system efficiency bellow threshold bank 1. On my way home from autozone, I was at a redlight and I noticed some sort of engine sputter and it was a lot shakier( I wish I could explain it a lot better but that is what I interpreted from it) this car has never done that to me. My car has about 1340000 miles on it. I checked for any leaks coming from the exhaust but I didn't notice anything nor did I hear anything rattling around in the exhaust. I started the car up later that day and the CEL remains on and I continued to check for leaks. This morning, I started up the car and was listening to the exhaust from the back and I did notice a rattling noise but it went away after a few seconds. I am pretty broke right now and I've been told that if it is the catalytic converter that it would be quite expensive. Is there anything else that could be wrong? Do any of the symptoms I have stated bring up any solutions? Any help would be great thank you.

Vic

 

o2 sensor...on my lancer had same code, replaced both o2's and cel went away.

 

Should I replace both of them or is there one of them that I should replace first?

 

A bad O2 sensor is an unlikely cause for P0420 in our Civics. In general, the cat is bad or there is an exhaust leak.

If you reset the ECU, does the code return?

 

I have not reset the ECU is there a proper way to reset the ECU on this honda?

 

take off negative cable off the batt or pull the fuse to the ecu

 

Ok, I did as you said and waited a few minutes before reconnection. The CEL light is no longer on. Does this mean it is the catalytic converter?

 

Drive the car and watch the CEL. If it turns on again, pull the code.

The Codes sticky describes the easiest way to reset the ECU.

 

I drove the car for about 12 miles and didnt notice the light, should I just keep an eye on it? Are there any recommendations you can give me? I have a young family and this is our only form of transportation so I am a bit worried about the car malfunctioning.

 

This^

Post again if the code returns.

When was the last ignition system tune up (plugs, wires, cap, rotor, ignition timing) done?

 

Ive done basic tune ups like oil, fuel filter, plugs, and wires

 

Cap, rotor, ignition timing?

 

None of the above. Are there links on the site that can help me with these procedures?

 

Do you live in NY?

 

No I live in the southwest. Not very many mechanics out here, especially for cheap, I want to learn how to do these things myself so I can perform them in the future but I do know people that could possibly help me but the problem is getting them to dedicate some time to help me out.

 

If there is no exhaust leak, then the cat is most likely toast. This generally happens because the engine is not given regular ignition system tune ups.

When the cat is dead, you should first tune up the ignition system and, when the engine is running properly, then replace the cat. This is one reason that you want to inspect the distributor cap and rotor. To do this, remove the distributor cap and inspect it for damage or cracks and inspect the inside contact points for wear and corrosion. Also inspect the rotor. Post pictures.



Please browse the FAQs sticky. There's lots of useful information there.

The cat only serves to reduce emissions, so when it dies, it usually does not affect performance unless it becomes clogged. A clogged cat can cause a loss of power.

 

I inspected for leaks when the engine was cold ( I also tried to plug it up with my hand but the pressure was pretty strong and I couldn't hold it for very long). Is that the best time to check for leaks? Tomorrow morning I will inspect the cap and rotor and post some pictures.

 

A small exhaust leak could throw P0420.

You need to carefully inspect the exhaust system for cracks and holes, and joints for gasket leaks, from the header to the cat. What trim -- EX, LX, HX, DX, CX? Is the car completely stock?

 

There's a diagram for adjusting the ignition timing in the FAQs sticky. You can probably get a free rental for a timing light at AutoZone.

 

Ok that sounds good. I will post the pictures as soon as possible. I didn't have time to do it today but I will keep you guys updated as soon as I do it. Thanks for the help it is greatly appreciated.

 

The car is a DX and is completely stock.

 

Look for a crack in the header/cat unit.