LX450 new owner needs help with O2 and Catalytic Converter Codes

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Joined
Dec 16, 2009
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3
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Location
The Garden State
Hi All,

Please do not get mad at me posting these questions. I know that I am new and probably dumb when it comes to these trucks, but I did a lot of thread searching and reading and still do not know what I should do.

My situation is this... I bought a 1996 LX450 with 128k about a month ago. Truck looked great, clean and drove very well. The PO bought it off a friend at 117k and only put on about 10k in the last 2 years, so it was sitting a bunch. Most service was Lexus documented with 30k, 60k, and 90k service performed.

So, I got the truck and did the 120k service, changing out all the oils, liquids, diff fluid, coolant flush, brake fluid flush, belts and hoses replaced, etc. The truck was driving better than ever.

Then, about a week ago I got a check engine light. Took it to a mechanic that I really trust and he said that the front O2 sensor went bad. He replaced it with after market (high quality Denso as he said they were OE). Got the truck back and it seemed to drive fine but the exhaust was very smoky when I was warming it up in the morning.. but hey, its cold outside in jersey. So, I drove it for a couple of days and got lean emission code, cleared it and took it to the mechanic who said that O2 sensors are running correctly and it was probably still my system adjusting....

A couple of days later got the dreaded catalytic converter code... the generic 0402 or whatever. So, I took it back to the shop and the mechanic said that the O2 sensors are working fine, but if you rev the engine to very high RPMS the readings sometimes are equal, indicating that the catalytic converter may be going bad...

So, my question is... can the back O2 sensor be causing all these problems? The check engine light seems to go on only after the truck has been driven for a while and its at the end of an hour long trip. Or is it because the front O2 was replaced with non OEM? Or, is the catalytic converter really going bad? I know this is probably hard to answer, but I really have limited funds so I want to make the right decision. The mechanic said that I can probably get away with replacing only 1 of the 2 catalytic converters to get the readings up to par and stop the code from coming back. Also, my wife freaks out whenever the check engine light comes on, and doesn't want to drive the truck anymore. It is running fine accept for the heavy exhaust smoke at warmup. Any help or suggestions would be appreciated!
 
iirc, 0402 isnt a cat code, its an EGR code. excessive flow i think, as 0401 is insufficient flow. looks like you need to check into your egr system. got FSM? welcome to the egr code club! :flipoff2:

edit: i doubt its your cats. 128K is not enough to blow them, but im not sure an 0402 code would cause them to fail. is it white steamy exhaust smoke? normal in cold weather upon startup. id get your egr checked. and if the denso 02 was a direct plug in replacement it was most likely not aftermarket.
 
Sorry, I think the code was P0420 I am pretty sure the tech said that it was a generic catalytic converter code. No leaks between the 2 O2 sensors tha would have caused the initial lean codes. I am hoping that its not the catalytic converter either, but don't want to throw money at another o2 sensor for the rear without understanding this better. The denso was a plug in 02 and ran me about $250
 
Aftermarket O2 sensors might throw codes on the 80 even if they are a direct fit. I've had trouble with the Bosch O2 sensors until I switch back to OEM O2 sensors. FYI...
 
Ok, I was thinking that the aftermarket may be the problem because all the troubles started after the initial OEM failed. But, again, something else could have made it fail in the first place. I am already out $250 for the sensor so I am leaning toward replacing it and the rear one with OEM and then seing if that fixes everything. Just wish wish I could get the problem diagnosed and repaired without this guessing game. Anyone can recommend a good Tech in New Jersey? I am going to a good guy but he doesn't specialize in cruisers. Thanks.
 
Before you go wasting any more money, I concur with baktasht, find out the EXACT code, it will pretty much tell you the problem. Post it up here, and mudders will be able to help you figure out what to do.
 
1) Get the Factory Service Manual (FSM). You can purchase it in book form or download it from TIS (check the FAQ).
2) Make sure you have the right engine code.
3) If you do have the O2 code, test the O2 sensors as per the FSM. It's a simple matter to test them and it can be done on the truck.
4) If they fail, call Cruiserdan and order a new set. If only one has gone out the other isn't far behind, you could replace just the failed one and hope the other one lasts but it'll likely go out rather quickly.

I would also check to make sure you cats aren't plugged as that will kill the O2 sensors. The front cat isn't easy to check, but the rear is. Simply unbolt it and shine a light through, and see how many of the "cells" are plugged up. My '96 with about 150k had less than a dozen plugged cells, out of hundreds. Make sure you get the gasket that goes between the cats from Cdan before you pull it, otherwise you will just have an exhaust leak. You probably need to replace the gasket anyway as by this point most of these trucks need them replaced.

I've attached the FSM document on testing the O2 sensors.
 

Attachments

My advice to people who get the P0420 code (possible O2 sensor problem) is to ignore it and buy a ScanGaugeII to clear it. If the code comes back right away, then you need to start troubleshooting the entire emissions system from cheapest to most expensive (O2 sensors, EGR valve, cats, etc.).

If the code doesn't come back right away (say it comes back every few months), then keep clearing it. I've passed California smog tests every year and I've been getting the P0420 code for 5 years. I passed my smog test yesterday/Saturday and I had cleared the code about 2 months ago.

So, I'm saving my money until the code persists on a daily basis -- meaning I clear it one day and comes back the next.
 
I would feel you paid a little too much for the O2 as a OEM Toyota list around $150.
Replacing just one is not a good idea as they both are the same age and since the front one went bad the rear one is probably getting slow/lazy (good reason you see the o2s reading about the same under load/high RPMs)
If no leaks then replace the rear one too then go from there .
I have got this code on my 80 and I replaced both o2 sensors and didn't have another problem till I got a exhaust leak between the cats , repaired it and was fine again till just last week as I got another leak .
At 128K its time to replace both anyhow
 

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