Hello Everyone.

So My 99 Accord EX V6 Coupe threw its check engine light the other day and I took it into Auto Zone to get read. This is what the code said:

P0420: Probable Causes:

1. A/F ratio concern
2. Air leak near HO2S (heated oxygen sensor) Bank 1
3. Ignition System Concern
4. Faulty Catalytic Converter

The first time I took it in, the Auto Zone employee said that it was probably a bad O2 sensor. I had the code cleared and then when it came back on, I took it in again. A different employee this time told me he was sure it was the CAT.

About the ignition system concern....what does that mean? Here is why I ask. Over 1 million Honda's were recalled for my year because they had a bad ignition. Here is what the recall said:

"ON CERTAIN SEDANS, COUPES, HATCHBACKS, AND SPORT UTILITY VEHICLES, ELECTRICAL CONTACTS IN THE IGNITION SWITCH CAN DEGRADE DUE TO THE HIGH ELECTRICAL CURRENT PASSING THROUGH THE SWITCH WHEN THE VEHICLE IS STARTED.
"WORN CONTACTS COULD CAUSE THE ENGINE TO STALL WITHOUT WARNING, INCREASING THE RISK OF A CRASH."

Now when I got the car, it had already had the ignition work done, but when I first got it the car it stalled out on me while driving a number of times. I started using my other set of keys and it got a lot better, but it still does it on occasion.


Basically I just need a wide range of opinions so that I can figure out what is the best thing to do about this code. You all probably know a lot more than me about this so.....LET THE OPINIONS FLY!

Thanks.

P.S. I have done a lot of DIY car work, just not on this car, so I might be asking later where stuff is located.

 

For the ignition switch recall, they apparently didn't redesign the switch to make it any better. You just get a new one same as the old one. Next time it goes out it probably won't be free. But it still might be the switch. Can you make the car stall by wiggling the key?

About the other stuff...
The rear O2 sensor is located IN the catalytic converter. Check it out for being kinda clean.

That sensor actually measures oxygen DIFFERENCE inside vs. outside. So an exhaust leak blowing onto the outside of the sensor will throw off the measurement. That can make the car "think" the cat is bad.

The "ignition system concern" they talk about in #3, is probably about misfiring. If you car has been misfiring, then it's dumping unburned fuel into the exhaust. This can be really hard on the cat, so think about whether something like that is happenning.

 

JimBlake,

Yeah I can pretty easily jiggle the key to make it stall...I can turn the key back hardly at all and it will go out. I also has a tendency to die when I go over like huge potholes and the like. If I am going above say like 25 mph, the car will die, and then a few seconds later kick-start itself back on, but any slower and I have to shift into neutral while rolling and start it again (which, by the way, it never has any problems restarting).

I have seen a lot of arguments about whether my year has one or three cats, do you know? Once I know where the cat is, I'll dig it out and look at the O2 sensor. When I get it out, can you tell me what I am looking for to know if it is bad?

I'll also do my best to look for exhaust leaks.

And my car hasn't been misfiring to my knowledge, I figure that would be an easily heard problem.

Another tidbit that might help....the day I got the car, it had just a few hours beforehand passed inspection, which means it also passed emissions. A week later the light came on.

Thanks for your help!

 

Looks like you have one cat, #3 in the picture below. The O2 sensor we're talking about is #18.



Ignition switch problem means you should replace the switch. Yes, it's been replaced before, but ????

I really don't know whether stalling (because of the igntion switch) could have caused a problem for the cat? It's really not the same as misfiring, because when it's switched off you don't have fuel either.

 

So you suggest I check out the O2 sensor, look around the CAT for any exhaust leaks, and replace the wiring harness for the ignition? There are two options for replacing the ignition: 1.) replacing the entire tumbler cylinder (mechanical part) or just the wiring harness by itself...I think I am going to try just the harness, I don't want two sets of keys, 1 for the ignition and one for the doors lol

anyways thanks for the diagram, should help a ton. I will keep any progress posted on this thread.

Thanks again!

 

I'd just replace the electrical part of the switch, not the key cylinder. Maybe as you take it apart you'll see something like loose mounting of a good switch. But more likely a flaky switch.

 

Yeah I am going to dig out the harness and see if I can see any damage...I am betting there is. Once I look into it I'll go pick up a new one, probably aftermarket this time, as Honda obviously hasn't fixed theirs

Anyways I just cleared my CEL, wanted to double check that another code hadn't popped up in the meantime....once it comes back on, I'll get it scanned again and write an update here.

For now, I am going to go try and see If I can figure out what part I am missing on my passenger seat...keeps sliding forward if I brake fast and someone is sitting in it.