bluemc

I'm getting the check engine light and went ahead and scanned it. it came up with P0420.

I know, I either have to fix the rear o2 sensor (i'm guessing the one on the cat) and/or replace the cat conv. I do hear a rattling noise when driving at slow speeds (bad cat. conv i'm guessing). I have reset the check engine to only have it reappear again after 30-50 miles of driving.

I've also noticed when I reset the battery to reset the check engine light. The car engine will shut off but after driving it for a while it will be back to normal and won't shut off anymore.

The car is a 99 Accord LX with the 4cyl 2.3L and has about 162,000 miles on it. I live in California so I can only use specific cat. conv.

I have to take the car in for a smog by August. I would like to replace the cat (only if it is the prob) and/or replace my rear o2 sensor.

I called to get the cat. conv replaced so far the prices are: $275+tax, $320, $300 and this is with a catco cat. conv that is welded on. I want bolt on so I can change it myself in the future.

For shopping for parts.
I found there are denso o2 sensors which are available that are much cheaper than the dealership and denso is the main supplier for honda o2 sensors.

O2 Sensor
RockAuto.com - $27.79 - DENSO Part # 2344621 Downstream
http://www.rockauto.com/catalog/moreinfo.php?pk=991606
* is this the correct sensor?

Converter Bolts/Nuts
http://www.hondapartsunlimited.com/f...EXHAUST%20PIPE
3 18176-PT0-003 BOLT, CONVERTER 3x $8.11
4 18176-P08-003 BOLT, CONVERTER 3x $8.11
27 90212-SA5-003 NUT, SELF-LOCK (10MM) 6x $0.37
Going to order 6x bolts and 8x nuts just in case and because their cheap. TOTAL = $51.62
* Seems expensive, could I get generic bolts/nuts and just use those and if so where and what type of bolts/nuts should I get?

Catalytic Converter CA Legal
RockAuto.com - $321.27 - MAGNAFLOW Part # 446615
http://www.rockauto.com/catalog/moreinfo.php?pk=3511788
Amazon.com - $330.31 inc S&H - Magnaflow 46615
http://www.amazon.com/Magnaflow-4661...1999&carId=001

I'm guessing, I will still need the gaskets if the Magnaflow doesn't come with them.
16 18393-SH3-S00 GASKET, PRE CHAMBER (52.5MM-53.5MM) $6.95
17 18393-SS0-J30 GASKET, PRE CHAMBER (57.5MM-58.5MM) $6.86

Checked for the gaskets and called RockAuto.com. They mentioned I will be needing the following gaskets not the original since I have an aftermarket cat conv.
WALKER Part # 31645 - $1.66 http://www.rockauto.com/info/Walker/...62712-0248.jpg
WALKER Part # 31383 - $1.81 http://www.rockauto.com/info/Walker/...62712-0248.jpg

Another problem being that the car is still on the regular catalytic converter and I assume it is rusted. I may just take it to the shop have them remove the bolts and attach the new ones on then drive it home and check the converter. If it's fully damaged then I'll replace it if I can clean it out. I'll clean it out.

Any help would be greatly appreciated. Learning how to work on the car and need some guidance here and there .

bluemc

Any advice?

bluemc

So I found the bolts I need. I'm just not sure if I need full threaded bolts or just the regular bolts for the catalytic converter to the down pipe and the converter to the muffler pipe.

doctorbee

Funny, I just did the cat on my '99 accord last weekend for the same reason too.

Tip, you may need to heat up the stuck on bolts with a torch and have at them with an impact wrench before they'll break free.

I got the Magnaflow 46615 direct fit because I needed it right away. O"reilly was the only place that had it. It comes with gaskets but does not come with bolts. It has no heat shield. I went to Home Depot and got some metric m10 bolts that are a little longer than the OEM studs along with nuts, regular washers, and locking washers.

The bolts had threads all the way though but if you want to use OEM exhaust bolts then that's the right (and more expensive) way to do it.

I fastened it like so (the same setup was provided by Greddy for my Civic's exhaust):

Bolt - washer - flange - washer - locking washer - nut

make sure you get long enough bolts.

It stalled after starting afterwards and I learned that the ECU has to relearn the idle based on the new A/F data. Start it up from cold with the petal slightly depressed and hold the throttle at 3k RPMs until the engine warms up.

Get it smogged and done.

bluemc

Thanks Doctor Bee for the reply.

I just recently replaced the Oxygen Sensor on top of the cat and cleared the code and it seems to be working fine. About 100 miles and the check engine light hasn't popped up again. So I won't need to replace the cat just yet but I think it needs to be replaced soon.

MAD_MIKE

O2 sensors become lazy with age. A P0420 code can be set off if either sensor is no longer in optimum condition. I'd replace the primary O2 along with the secondary. The primary monitors the engine A/F ratio, if this becomes lazy it will not switch correctly. It may not set a primary O2 sensor code, but it will greatly affect how the engine runs and how well the catalyst can function.

doctorbee

If you're worried about funds I'm talking to www.converterguys.com about recycling my old cat. They're offering $220 for my old 4cyl California edition cat I'll let you know how it goes.

doctorbee

SWEET! just got my check for $220 from www.converterguys.com for my old, busted, rattling, inefficient cat

bluemc

I guess, I am going to have to end up getting a new cat conv. I replaced the o2 sensor but can still hear the cat conv rattling and car tends to act funny.

Do I still have to replace the o2 sensor again? I'm guessing, I would have too as it's better to have it brand new since I am going to put in a new cat conv?

I have bought Magnaflow #46615 and o2 Sensor, Spark Plugs, Gaskets. Total Price of $374.26 with shipping.

Bought bolts from BoltDepot total of $27.88 with shipping.

Total $402.14 - $220 = $182.14

Thanks DoctorBee for that heads up. I have already emailed them and hope to be able to get $220 for my CA conv. too. That would be nice and make the fix a better price.

my cat conv is pretty much corroded to the pipes. I have the stock one on it, How'd you get yours off? I don't have the necessary tools and probably don't want to heat it up so I might just bring it to the shop and have them take it off and bring it back home and screw the new one on.

What do you think?

doctorbee

Don't worry about the oxygen sensor.I reused mines without a problem.I used a propane torch
And pb blaster to get the bolts loosened. Had at it with an impact wrench and it came off. You can ask for help from a shop if you can't

doctorbee

Ask them to loosen the bolts for you

doctorbee

Worst case just cut the bolts off on the cat side and pop them off the flange

slowcivic2k

P0420 is caused by the rear O2 switching at the same rate and front, indicating a bad converter. The O2 sensor will never be at fault for this code, ever. The computer must test this sensor before it tests the converter. If there is a rear O2 sensor code, you will never have a P0420 until you fix it and it can run the catalyst monitor test.

Just blow the nuts off the converter side of the flange with a torch, remove it, and then heat the area around where the studs meet the flange, and tap the rest out.

The O2 sensor may get stuck in the converter, with varying degrees of success getting them out, it may break free, it may break free with the threads gone, or wont budge.

No shop should remove a converter without putting another one on or putting the old one back, it is illegal for any shop to remove an emissions device from any vehicle, or render an emissions system inoperable without reinstalling or replacing said part. Keyword there is reinstalling it....

Peter01

Hi bluemc,
I need to replace my catalytic converter on a California 2000 Honda Accord LX, with a 4 cylinder ULEV engine, in the next 3 weeks. Is there a difference between the MAGNAFLOW Part # 446615 and part # 46615? Amazon has a slightly better price on the 446615 right now.

http://www.amazon.com/Magnaflow-4466.../dp/B00861LG44

I also noticed that the different sellers on Amazon have different return policies. A better return policy is probably worth paying extra for. Also, RockAuto has a great return policy. Thanks for the links to them.

Please describe the lengths and sizes of the bolts you bought at BoltDepot. That looks like a good deal.

Thanks,
Peter

doctorbee

446615 is the newest model. i got 46615 for my accord

Peter01

Thanks for the information doctorbee. I purchased the catalytic converter ( Magnaflow 446615 ) and the O2 sensor from RockAuto today.

doctorbee

you can get cheaper bolts from Home Depot. I got ones about 10mm longer than stock to accommodate the extra washers

it cost me like 10 bucks and i didn't have to wait for shipping.

Peter01

It looks like I won't replace the Cat. Conv. after all. After resetting the Engine Maintenance light the third time, it didn't come on for 50 miles so I took the car to the smog check place and it passed. If the measured levels were five times higher it still would of passed, so I think the Cat. Conv. is doing its job. The light came back on at 55 miles from the reset though. I will replace the o2 sensor and see if the light stays off. I already replaced the air / fuel mixture sensor with Bosch part # 13493. I am thinking of replacing it again with Denso part # 234-9025 if the o2 sensor doesn't keep the light off.

I don't want to replace the CAT now because it will be 2 years before I will have the smog check done again to make sure it is working and by then it may be out of warrenty. CA law requires that all tests be reported, so it doesn't make sense to have it tested when not required.

MAD_MIKE

Bosch O2s are crap. Only use Denso, NTK, Delco/Delphi brands.

Peter01

Thanks MAD_MIKE! I will replace the Bosch O2 and return it. I will use a Denso since the original part was a Denso.

doctorbee

i did this trick a couple times too but needed to replace the cat after it sounded like a can of marbles.

doctorbee

update for you non-cali folk with ULEV accords:

According to magnaflow Ulev 49 state cat is pn 51912

Lost Again

Very nice, updating your posts with what you have learned

Good job

dglarsen944

I have a 2002 Honda Accord EX, 4 door. It's a ULEV accord with 212,000 miles. Owned it since new.

I need to replace the cat conv as its making a noise inside. I removed the heat shields just to rule them out. Sounds like loose material inside. More noticable when at idle.

Deciding on replacing with either:
>Magnaflow part # 51912 for $233 (Amazon 49 State Calif compliant) or
>Honda OEM part # 18160-PAA-305 for $550 (Majestic Honda online 49 State.....not ULEV)

I don't live in California. I'm concerned about not being able to use the heat shield on the Magnaflow Cat Conv. There doesn't appear to be any holes to mount the Heat Shield bolts to. Any thoughts or experience to share?? Do you need a heat shield with the Magnaflow???

1.6si

I have a '99 Teg Ls stock engine w/ 5 Spd with 130K miles in Az. & I'm getting a P0420 error code.

Slowcivic2k stated P0420 is caused by the rear O2 switching at the same rate and front, indicating a bad converter. The O2 sensor will never be at fault for this code, ever. The computer must test this sensor before it tests the converter. If there is a rear O2 sensor code, you will never have a P0420 until you fix it and it can run the catalyst monitor test.

Sorry but I'm new to O2 sensors & started working on my car since $$ tight.

So a P0420 is a bad Catalytic Converter ? And not a O2 sensor ?

Thanx for clarifying.