Hi,
I have 97 honda accord (Ex, 4cyl Vtec). My wife is driving this car when it rains outside and it does rain a lot around here. Recently the car started dropping RPMs and loosing power (of course this only happens when my wife is driving the car). CEL didn't come on when it happened. I took a car for a spin, I haven't noticed lack of power (knowing it is 4 cyl car). I drove the car to work a few days ago and the check engine light came on. I stopped by O'Reilly auto parts to read the code. It was catalytic converter P0420. So I read a bunch of threads on this issue and figured out I just need my catalytic converter replaced. Talked to friend of mine who is a good mechanic and he suggested loosing the bolts on catalytic converter up stream. The bolts are heavily corroded and I was afraid of breaking them. I haven't tried WD-40 yet. Yesterday my wife was driving the car again and it died. She said the RPMs dropped and the engine would not start. When I came to pick her up the car started just fine and we were able to drive it back home. CEL didn't come on. I happened to borrow the code reader from coworker that reported P0130 (with P0131 stored) which is pointing to oxygen sensor upstream.
The code reader I have doesn't provide live data, so I cannot read voltages reported by oxygen sensors. What are the chances that both catalytic converter and oxygen sensors went out at the same time? A few months ago I had the EGR error code. Cleaned the path and haven't seen it back. Then the car wouldn't start. I inspected main fuel relay, didn't see any issues and had it resoldered just in case.
I haven't check my spark plugs but it's been 42000 miles since I changed them with distributor cap and rotor. I also had igniter replacedn about 40000 miles ago. The accord has been very reliable car until recently. I am in 19x000 mile range.
Should I replace oxygen sensor first or go for catalytic converter? I plan on driving the car in the meantime with error code reader handy. I believe oxygen sensor and catalytic converter errors have to happen twice to trigger CEL.
I filled up the car to check the gas mileage and I've got about 26.2mpg. Taking into account local traffic it is probably fine. Oops. Just pulled up mpg rating and it is rated at 20/22/26, so it's fine.

 

The catalytic converter code will set if it doesn't see a difference in value between what's going into the cat and what's coming out. Hopefully replacing both oxygen sensors is all you need. Replacing the first oxygen sensor, if faulty, could fix your car stalling issues as well so you could be killing two birds with one stone. The worst case scenario is that your cat is actually bad. But you don't want to replace that unless the code comes back after replacing the other two.

You can get the oxygen sensors from rockauto.com google search "rock auto coupon code" before buying. Make sure to only get "Denso" oxygen sensors. You can normally rent an oxygen sensor socket from most parts stores.

 

Thank you for the reply holmesnmanny.
I reset the errors yesterday. When I got home I read temporary DTCs with the code reader and found error 67-01 with multiple instances:
1. Catalyst B2 deterioration
2. Catalyst system efficiency below threshold
3. Catalyst system efficiency below threshold
4. Catalyst system efficiency below threshold B1
5. Catalyst B2 deterioration
6. Catalyst system efficiency below threshold
7. Catalyst system efficiency below threshold B2

So I assume it is time to swap catalytic converter. O'Reilly auto parts is going to have it in stock tomorrow, so I am going to have it replaced. I will let you know how it goes.

 

You're replacing the catalyst before replacing the O2 sensor, which is setting a code? A faulty O2 will cause a PO420 code.

Replace the primary O2 first.

 

Would I get "Catalyst system efficiency below threshold" error with faulty primary O2 sensor? Based on information I was able to find the faulty O2 sensor wouldn't cause P0420 that's why I thought I should replace catalytic converter.

 

The secondary O2 monitors catalyst efficency, if it falls below threshold, P0420 will pop up. A faulty primary O2 or any other issue not allowing the A/F ratio to be withing spec will not allow the catalyst to catalyze correctly, too much or not enough fuel or too much or not enough air will not create the ideal mixture to allow the catalyst to function properly.

Even if you replaced the catalyst, that doesn't fix the problem of P0130 & P0131. Fix the primary O2 issue first.

 

Mad_Mike,
thanks for recommendation. I will try to measure voltages on both sensors with engine running. Perhaps local stores have code reader with live data.

 

I checked rockauto parts online and also found coupon. Thank you. The sensors online much cheaper then at retail stores. Oreilly quoted $68 for one, when I called different location the guy recommended to get $85 one. I see the cheepers sensor with ULTRAPOWER part number claimed to be manufactured by Denso. I assume I should stay away from it and get sensors with Denso part #?

 

Yes, just go Denso.

 

Do I have to use California complied cat converter if the sticker on my car says it complies with CA emissions?

 

I you live in CA you will have to use a CARB/EO approved replacement catalyst, doesn't matter if it is a Federal or CA car.

If you are outside of CA it is whatever the states laws are.

The reason for CA spec'd catalysts is that replacement units were not made up to snuff and were failing smog checks less than two years after installation. CA had to mandate CARB/EO approved units to be used as replacements thanks to the scam.

 

It all depends on if you want to replace the cat even tho it may be still working fine.

 

Thank you for the replies guys.
I had catalytic converter replaced. The car had CA approved converter that is much bigger. The mechanic had to heat up the 3 bolts that connect to exhaust as the new one didn't include them. He had to weld those 3 bolts to the new converter. I bought not CA approve converter, the support bracket is not compatible with this one but the new one is a lot smaller and doesn't need any support. I may mod the support in the future though. The old converter is plugged up, I saw a very small dot of light when I was looking through it.
I cleared the code and the car was driving fine. More low end torque (can be placebo) but surely feels more responsive. Though it died when I almost got home. The RPM's dropped to 0. I was going up heel when it happened. I pulled over and checked for error codes: no error codes. I tried to start it a couple of times with no success. Waited a few minutes and it started.
I am not sure what to do next. Upstream oxygen sensor, distributor...

 

So you spent ~$300 on a catalyst rather than ~$30 on an O2 to fix the P0130 and P0131 codes and drive-ability issue?

It will take a few drive cycles for a code to pop back up after you cleared it.

 

I am really at a loss for words on this one, mike. Like I've said before, people are going to do what they want to do. This is one such case.

 

I will keep you updated once I find out what it is (if you are currious).

 

I believe the great phootbag once told someone, paraphrasing, " I can no longer help you..."

I miss that guy.

 

It's funny you have said that.
The catalytic converter was plugged up with broken pieces inside as I can hear them rattle. It cost me $152, not $300. I was getting P0420 all the time. I think I did the right thing. We will see if P0130 ever comes back.
As far as engine idle problem I belive it is ignition module as I have desoldered main fuel relay. It looked clean even before. Here is the thread on that
https://honda-tech.com/forums/engine-management-tuning-124/can-bad-o2-sensor-cause-stall-2542753/
I don't think bad O2 sensor will cause a stall, but I am not a mechanic.

 

It doesn't take long for a new cat to get destroyed by an improper fuel mixture due to a faulty oxygen sensor. Trust me I know this by experience.

If you're certain that an oxygen sensor won't cause your car to stall then you should already know how to fix your issue. Good luck.

 

I had the oxygen censor replaced with brand new O2 censor body of mine bought for his Acura. Same plug except cable a bit longer. It could be the wrong oxygen censor but P0420 went away and intermittent engine stall issue came back and I dropped the car at shop. I did pass the smoke test before I dropped the car at the shop. Not to go into details there, the car is back and so is 6-7 CEL light (just happened today). Could it be a bad fuel filter or second O2 sensor? I will try to use my cheap bluetooth error code reader to read the voltages on O2 sensors.

 

Each O2 is calibrated to a specific ECU. Some part numbers cross platform,but this is very rare. Get the right O2 for your car.

Anytime you have O2 codes and Cat codes. You ALWAYS deal with the O2 codes first, and then retest. If the vehicle is not in fuel control(limp mode or default) then it will not be running stoich and the emissions emitted will be more than the catalyst can handle. Subsequently you will get Catalyst codes.....



(also if you do not get an OEM cat or a CA approved cat,you run the risk of a returning P0420. It is hit or miss with aftermarket cats....)

 

OP, you should check for an exhaust leak.

 

thank you for the replies guys. I've found this article on how to test oxygen sensors (lean and rich conditions) though there were no pictures on what hoses one suppose to disconnect. I've test lean condition by disconnecting the vacuum hose shown on the picture with two clamps. The voltage on downward O2 sensor dropped to 0.16V not 0.1V. I am not sure if this is even the right hose. Also I don't know what hose to remove to test for rich condition.

 

I'm fighting a similar issue - P0420 code. I read the article you mention and tested the way he explains. For lean check, the PCV hose going into the valve cover (as shown in his pic) is the right hose (according to him). For the rich condition, he says to use the vacuum hose going to the fuel pressure regulator. You can find a pic on internet or exploded view in this thread. The vacuum hose is the small one coming out of the top.

My dilemma is that I still don't know the cause. I believe I have a bad cat, but how it got bad is the $64,000 question. As others have pointed out, replacing a bad part without knowing how it got that way, might lead to replacing it again (and again).

 

This particular code is almost always a bad cat. You can try to replace both o2 sensors first, assuming they haven't been replaced recently but odds are it's the cat.