P0 420 Code On 95 Lexus

[Jacob]

I own a 1996 LS400 with 120K. I bought the car about 7 months ago with 113K (and a check-engine light). I have both P0420, and P0430 codes (both banks). I replaced the pre-cat oxygen sensors but the light didn't go away. I only use premium gas and the only long trip I had put on the car was Phoenix- Los Angeles- Phoenix. I still haven't checked the rear oxygen sensors which, I believe, requires the removal of floor carpet. I hope that those sensors are bad since I'd never buy the outrageously expensive cats.

Good luck with your car

Jacob

[srgilbert]

Oddly enough the drive side rear sensor was throwing out a code until the long highway run. Now it seems as though that problem has gone away and I'm left with the p0420. I do not understand how the cats work however it's odd that I could run 300 miles without the failure....Is anyone aware of a fueal additive that will cause no harm but might clear up the cat problem? I only have 106K on the LS.

I own a 1996 LS400 with 120K. I bought the car about 7 months ago with 113K (and a check-engine light). I have both P0420, and P0430 codes (both banks). I replaced the pre-cat oxygen sensors but the light didn't go away. I only use premium gas and the only long trip I had put on the car was Phoenix- Los Angeles- Phoenix. I still haven't checked the rear oxygen sensors which, I believe, requires the removal of floor carpet. I hope that those sensors are bad since I'd never buy the outrageously expensive cats.

Good luck with your car

Jacob

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[95LS400Bob]

Not sure about the wiring. Probably runs under the carpet.

Will the cats switch right to left? Not sure if they will but that would also tell something.

Federal law against selling used cat converters. So wrecking yards don't do it. Muffler shops are supposed to keep count of the converters they replace or they get in trouble with the Feds.

Performance wise..this code is not hurting anything. The computer checks and compares between the front 02 and the rear 02 and if a problem sets the code. But no engine tuning parameters are changed.

[pachocco1]

I figure that you don’t have a manual. Here is some pertinent information.

An update on my saga -  I continue to get a P0420 code weak bank 1 cat on my 95LS400.  I've replaced the front oxygen sensors with Densos and the problem did not go away.  I took the car on a 300 mile trip last week after the ECM reset and the light came back on after 250 miles.  I reset the ECM once again and I managed to get another 300 miles antil I hit town driving and the light  came back on again .  Today I planned  to flip the rear sensors as suggested to see if the code goes to P0430 which will point to the other cat however I could not figur out how the rear oxygen sensors are fed through the frame - they are held in place with grommets to the body and I cannot seam to trace the wire after that to find the connector.    I checked with Lexus and the cat is roughly $900 which is not an option.  I'm finding that used ones do not seem to be available through junk yards due to EPA ....

Any thoughts?  ANyone with the same experience?

THANKS!

I would swap the rear 02 sensors. If the code sets up again..then I would have to say the cat might be the problem. But if you get a right bank code(P0 430)..then that would prove the rear 02 was bad. That is how I would do it before buying a cat.

I haven't been getting the P0 420 code anymore. But that is my plan if it happens again. I have pulled both my cats off and looked at them and they are not broken inside and look fine.

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comp.pdf

insp.pdf

cip0420p.pdf

[Jacob]

Here’s a link to a catalytic converter cleaner:

http://www.autobarn.net/chcat-1.html

I considered using it but was afraid that it might harm the car.

[chubyball]

I have had this similar problem for two years and now still got the same head ache. I thought the technique of swapping O2 sensor is a brillion idea, and some of you had replaced the O2 sensors and I did replaced both cats but still have the same problem.

I thought sometimes it had to do with the gas that where you got. The last time, I drove 500 miles and Engine light is ON again, P0420 thredhold bank1. I had no idea what is this code for? CATs (I replaced both already), may be O2 Sensors, may be Gas, or leaks somewhere?

Second thought, I can think of is may be leaks between manifold and engine. Sometimes I smell unburn fuel from underneath engine. Someone at Autozone to me to use a gas torge and had it on without and fires while keeps the engine running, this way, you can tell any leaks. If there are some leaks then you should see alot of sucking from that area, it's trying to draw all the gas in that leak.

Anyone here succesfully fix the problem? I am think getting rid of this car 147Kmiles 95' LS400

[srgilbert]

I have had this similar problem for two years and now still got the same head ache. I thought the technique of swapping O2 sensor is a brillion idea, and some of you had replaced the O2 sensors and I did replaced both cats but still have the same problem.

I thought sometimes it had to do with the gas that where you got. The last time, I drove 500 miles and Engine light is ON again, P0420 thredhold bank1. I had no idea what is this code for? CATs (I replaced both already), may be O2 Sensors, may be Gas, or leaks somewhere?

Second thought, I can think of  is may be leaks between manifold and engine. Sometimes I smell unburn fuel from underneath engine. Someone at Autozone to me to use a gas torge and had it on without and fires while keeps the engine running, this way, you can tell any leaks. If there are some leaks then you should see alot of sucking from that area, it's trying to draw all the gas in that leak.

Anyone here succesfully fix the problem? I am think getting rid of this car 147Kmiles 95' LS400

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Can I ask what brand CAT you purchased?  I have DEC converters on order which are direct bolt ups.  Price is $120 each.  I guess if this doesn't solve the problem I'm getting out the black electrical tape and the light will be off.

[95LS400Bob]

I haven't had any check engine lights and no problems whatsoever. BUT..I have not driven the freeway for any length of time...which is when I would get a P0 code. After watching guys checking, swapping and replacing the 02's front and rear...and even replacing the cats and still getting the code....my thoughts are that this is and ECU glitch.

Since when the code is set there is no change in engine tune...I believe I will just ignore mine if it comes on again. And get out the electrical tape to cover the light. And surely the code will appear again if I take a long highway cruise.

And mine just got through the smog test with flying colors....like it always does.

[srgilbert]

I haven't had any check engine lights and no problems whatsoever. BUT..I have not driven the freeway for any length of time...which is when I would get a P0 code. After watching guys checking, swapping and replacing the 02's front and rear...and even replacing the cats and still getting the code....my thoughts are that this is and ECU glitch.

Since when the code is set there is no change in engine tune...I believe I will just ignore mine if it comes on again. And get out the electrical tape to cover the light.  And surely the code will appear again if I take a long highway cruise.

And mine just got through the smog test with flying colors....like it always does.

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I would be it is the ECU but I am aware that the cats for 95 were weak - confirmed from several Lexus mechanics. WIth only 114K on the LS my guess this is part of the enture ECM fiasco for that year. Every once in a while the trans acts a bit funny on the 2/1 downshift but overall it is running better than under the old ECM. I'll let everyone know how the cat replacemetn goes. FOr $120 a piece with free delivery and direct bolt ons and warranty other than crawling under the car a bit I have little to loose. I do have the electrical tape ready.

[srgilbert]

Just wanted to provide some future reference on this topic. I went ahead and purchased 2 aftermarket direct fit catalytic converters - total about $270 delivered and had a local shop put them on. I watched as the studs broke off while removing the frozen nuts....after drilling them out and replacing them the cats were on. About a 3 days later later the P0430 code came on which points to the post cat oxygen sensors. I purchased 2 Denso sensors (universal 4 wire) via Ebay and spliced them in as instructed. Actually this was much easier than pulling up the carpet in the cabin. I checked the resistence on the black wires and they were both 8 or so ohms which is above the standard. The sensors are in and the check engine light has been off for a week. I believe this one can now be considered completed.

The lesson I learned is that it is well worth your while to replace the oxygen sensors (all 4) before the converters unless there is an obvious problem.

[Jacob]

Thank you for the information srgilbert. I have a '96 with the same problem and I really would like to stop seeing the orange light.

Thank you

[srgilbert]

Thank you for the information srgilbert. I have a '96 with the same problem and I really would like to stop seeing the orange light.

Thank you

I/,m so used to seeing the orange light that I thought it would burn out before I managed to solve the problem. It's odd tht the emission test passes with flying colors but the ECM finds a fault. Perhaps Toyota should have allowed some greater tollerance before the stupid light goes on...hope all of this helps.

[nc211]

this is probably coming down the line for me....what sound and noise improvements did your aftermarket cat's make for your car? and where did you get them from?

thanks

[srgilbert]

this is probably coming down the line for me....what sound and noise improvements did your aftermarket cat's make for your car? and where did you get them from?

thanks

I purchased (2) for $278 from :

Import Specialists of America, Inc.

990 Cedar Bridge Avenue

Building B7 - Suite 221

Brick, NJ 08723-4157

The exhaust is slightly louder however no change in performance. The package is almost identical in size. I really did not want it to behave much different than a LS should behave. Good luck!

[eddieg]

I am a bit confused I have code P0420 which is Bank 1 efficiency but I am told by a mechanic that Bank 2 sensor is bad based on the O'scope below. I already had bank 2 sensor 2 replaced which did not solve the problem. What do you guy's think?

[Hampton]

I am a bit confused I have code P0420 which is Bank 1 efficiency but I am told by a mechanic that Bank 2 sensor is bad based on the O'scope below. I already had bank 2 sensor 2 replaced which did not solve the problem. What do you guy's think?

Hope me experiments may help: [95 lexus ls400 95km]

My first time got a engin light on is Junn,2005, when I deep gas panel for a up hill acceleration, the check engin light on,I took the car to local lexus dealer to fix it, here is their report said:

Condition:Check engin light on

Lack if acceleration up hills

Casue: Code P0430-catalyst system efficiency below threshold (bank2)

Correction: Possibly catalytic convertor-bank2 require replacment, cleared code for now,customer to monitor

After two month local driving, check engin light got on several times when I deep gas panel for accelaration when uphill driving. each time I try to diconnnect the battary to get rid of that annoy light. it didn't work long for sure as you know, the light went back. Finally, I do two things which I think it solved the probelm:

1: Clean the MAF [Mass Air Flow]sensor, as I undestand it will send ECU wrong signal if it was covered by dirty or dust, a wrong or rich gas and air mixture will cause a higher emission which brings the check engin light on.but be carefull to clean that sensor, here is the pictue guide: http://www.lexusownersclub.co.uk/knowledge...ex_v2&id=50&c=9

2: Clean the Throttle body as guided by http://www.lexls.com/tutorials/EFI/throttlebody.html

The above two URL are 91 ls400 model, 95 ls400 just a little differnet.

Since then I've never got the check engin light on

Enjoy your ride!

[chubyball]

My question is after replacing the OXYGEN sensors, do I have to reset the code or it will reset itself. Thanks!

[chubyball]

Hey guys, I replace 2 back Oxygen sensor and the Engine Code has not appeared since, it's about 2 weeks drive now, nothing shows up yet. Keep fingers cross. The problem cause, since I put a cheap gas 89 octane 3 years ago in the tanks and the yellow light has not been gone until I replace 2 cats, and last weeks I just replaced 2 OxSensor.

[chercom]

After a highway cruise last night...we got a check engine light. So went to Autozone and read the code P0 420. Read the diagnostic in the manual and basically it means the 02 sensor before the cat on the left bank is not seeing the same "wave" at the 02 sensor after the cat.

So..those of you who are up on this....If I had a bad 02 I figure I would get an additonal code telling me rich/lean whatever. But I only have one code.

So, I figured maybe I better look at the cat. So I pulled the exhaust pipes off right at the cats...started and ran the motor. Exhaust felt equal coming out. So no plugged cat or anything.

Then I pulled the cat off the left side (takes forever as bolts are frozen...don't do this unless you want to spend the day) and looked through the left side cat...all looks fine..no broken pieces and everything clean.

So I reinstalled everything...reset the light. But it will probably come back on again after another cruise.

Anybody been through this? I know Bad 02's are possible...but wouldn't I get another code?

My check engine light recently came on. The dealership tells me that I need to replace both converters. The diagnostic codes were p0430 and p0420. Do you know where I may be able to find two converters at a reasonable price. I found several sites on the internet but they don't have genuine Lexus converters. Any ideas.