OK, so I have a 0420 code. Bad Catalytic Convert. Before I spend the money and change the cat I wanted to check on one thing. It was my understanding that the computer in the car will not check secondary O2 sensor readings until the car has had a chance to warm up. However, my car has the Bank 1 Sensor 2 jumping all around from the moment I start the car. Bank2 Sensor 2 reads minimal until about 22.8 seconds after starting it and then it begins to show some fluctuation.

My question is this: Is my cat bad? Is my computer bad? or do is there something else wrong with my car?

Any help would be appreciated.

Thanks,

 

I would go with the 02 sensor telling the ecu that the cat is bad. I would replace the o2 sensor first. The cat has to heat up to work and at start up it isnt doing anything.

 

Has the car even gone closed loop? Probably not.

O2s are a wear item, so maybe change it anyway.

 

Thanks Avern1 and Jag V8,

Why is it that the parts that go out first are always the hardest to get to? I will order up an O2 bank 2 sensor and see if that fixes the problem before I move to replacing the catalytic converter.

 

Update: I wanted to follow up in case others are waiting for me to figure this one out before they start spending money on repairs.

Situation:
p0420 code. Running lean, Catalytic converter problem code.

Symptoms:
CEL, Smell of burnt rubber or oil after running it in under load. Bank 1 Downstream O2 sensor does not seem to wait before the engine warms up before it starts sending fluctuating codes. After it warms up it seems to be the same or close to the same as the Bank 2 Downstream O2 sensor.

What I have done that did not work:
Cataclean, BG44 (Twice).

What I still have yet to try:
Check the Temperature at each side of the Cat to see if the Cat is burned out.

Need to replace the Valve cover gaskets on that side as they are leaking. May have sent oil into the Cat to coat and possibly burn out the cat.

Swap O2 sensors from side to side to see if the code changes.

Replace Sensors or Cat depending on the problem.



Please let me know if there is anything else I should try before I spend the time and money on replacing the Cat. I understand for the bank one cat it is probably not a home repair project.

I will keep you updated as I continue to find a solution.

Thanks again for all the help.

David

 

Dave: A leaking valve cover gasket can cause damage to the catalytic converter, but not by "sending oil into the Cat".

When valve cover gaskets get old, engine oil leaks into the spark plug wells causing the spark plugs to misfire. The misfiring plug does not burn fuel inside the cylinder like it should, so the unburned fuel flows out the exhaust valves and into the catalytic converter, where it is 'burned'. The catalytic converter is designed to burn a small increment of residual fuel normally found in engine exhaust. But constant misfiring feeds too much unburned fuel into the catalytic converter, causing it to overheat, eventually damaging the catalyst.

Fortunately, this won't occur without some warnings. Misfires will trip the check engine light and cause error codes P0300 to P0306, in addition to a rough idle. And severe misfires will cause a very rough idle, plus the check engine light will blink constantly, warning you the catalytic convert is at risk of being damaged by overheating from too much unburned fuel in the engine exhaust.

Hope this helps.

 

I appreciate your letting me know about the warning signs. Unfortunately I bought the car and the 0420 code showed up right away. s, I do not know if the car had misfires in the past. I do know the typical intake gaskets were a problem and the tried to fix them using a liquid gasket. I have replaced all of those and the PCV hose.

I wondered if residue from the Oil was coating the O2 or the Cat causing the O2 sensors to read incorrectly. It sounds like that was a wrong assumption on my part. Thanks for the clarification. I still see people who are replacing Cats only to find out they still have the 0420 code and I would rather not do that if I can avoid it.

One day soon I hope to get under the hood and check the things I mentioned earlier so that I can finally post a resolution to this issue.

Thanks again for all the help everyone.

 

Hi ddsand,
Before the catalytic converter is damaged beyond use on a Jag, other elements that work with it would have damaged also. So my advice is to change all 4 O2 sensors, you can't be thinking of chaning the cat when your sensors are not in order. Bad O2 sensors can damage a new cat. Good luck.

 

Thanks Mrqng,

I will start there and see if it works. I appreciate everyone helping me find the smart way to spend the repair money.

I will report back.

 

So one year later I finally got around to changing the 02 sensors on the car. What do you know. p0420 code is now gone and she just passed safety and emissions. I should have listened to you guys a year ago when I bought the car.

Thanks for all the help.