LsAlex

Ive been on other forums, and I do understand the search feature. I have searched through the forums and found nothing quite like my situation.

I bought a 98 ls400 with 160k miles on it a few weeks ago. I bought the car with a bad 02 sensor, showing a p0135 code. I replaced the 02 sensor and the CEL went away for a good hour, then on my way back from town my CEL comes on AGAIN. I go to the local autozone and get it read with 2 p0430 and 2 p0420 codes, meaning that my catalytic converters are below the threshold.

after doing research, I figure out there is a plethora of reasons this could be happening. Spark plugs, intake leak, bad ECU or even the obvious, bad cats.

my question is, why would both of these codes show up at the exact time, and twice? Another person on this forum seemed to have both codes twice and tried everything, then eventually replace the spark plugs and resolved the issue.

There is also a small amount of steam/smoke coming from the exaust even after being warmed up and driving for a while. I would just replace the cats and see if that resolved it, but thats quite alot of cash to drop and Id rather get some more advice.

note, that I did change the oil, use seafoam and cleaned the throttle body and MAF with the correct cleaners and made sure there was not a single intake leak along the boot. Id really appreciate some advice, although I feel that I have looked into these codes heavily. Thanks!

timmy0tool

iTrader: (7)

I would avoid replacing the cats until you do the simple stuff first like changing the plugs as you researched.
it is very possible the other downstream sensors are bad too and not reading properly.

as for the smoke, these cars are known to have power steering leaks from the air valve into the intake which results in it burning off during startup primarily, though I cannot recall at the moment if this is only for pre-98 cars...I'm hungry!
https://www.clublexus.com/forums/ls-...ystem-diy.html

oldskewel

iTrader: (1)

And regarding the white smoke, even with the PS completely tight, not burning any PS fluid (common on these cars, at least the older ones like my '91), these cars do put out a little more condensing vapor out the tail pipes than most cars do. So that's normal. Even worse with cold and humidity - got any of that in WA right about now? Yes, different and maybe surprising, but I would not worry about that one for now.

Sorry, no real advice on your codes. But in general, I'd recommend to buy your own scanner. Voltmeter too. They'll pay for themselves the first time you avoid replacing a part unnecessarily. Also general advice on codes - consider them more of a clue than an answer. They got set because some sensor somewhere crossed a threshold, but what the actual problem is may not be clear.

Welcome to the club and good luck. Thanks for the well-described problem in your first post.

Fit1too

I agree with oldskewel, that the "codes are clues". I've read a lot about changing only one oxygen sensor at a time. Some believe they need to be replaced in pairs i.e. both front (upstream) or both rear (downstream). Some say to do all four at once. Rockauto has good prices on their O2 sensors. I believe Denso is the OEM replacement.

jaaa

Many possibilities here. Since you just bought your car, you really have no history on a lot of things. The prior owner could have cleared his codes out prior to selling the car to you. It takes many miles for the car to process the cat information and then to set the 420 and 430 codes. The first thing to do is to get your car up on jack stands and while the car is cold, start it and feel for an air leak just past both catalytic converters at the flange where they meet the Y pipe. My leaks were at the top of both flanges. The reason you do this with the car cold is those flanges will get very hot and a burned hand could occur. This is a very common problem on LS400's. I would do this test before buying anything.

gebo

How did you fix those leaks?