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Gs400 Catalytic Converter Gone Bad - All 3 Banks


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I was wandering if anyone knows how many cat. converters GS400 has? I've been given different info from different sources. Also, since the car is 13 years old and has 300,000km on it i don't think its feasible to install OEM. Any suggestions/tips on aftermarket cats?

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I was told by Lexus sales manager that there is a third one which is right at Y pipe somewhere in the middle. Is this Bank 3?

Why is the sales manager talking about an exhaust system? I suspect you have an MIL for catalyst inefficiency and the tech working on your car would rather use "shotgun diagnostics" rather than pin-pointing your concern. BTW, the '98 GS400 has two catalytic convertors (Three-Way Catalyst). One on the left bank (bank one), and one on the right bank(bank two).

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There is a resonator in the middle (on US cars). It may be a cat on vehicles in certain markets, such as Canada. Since you have not identified the country/region in your profile, I cannot be more specific. I agree with the note above, the technician may not be fully accurate in his diagnosis. It is rare to see multiple cat failures simultaneously without some outstanding cause. If it were me, I'd get a second opinion.

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  • 3 weeks later...
  • 3 months later...

There is a resonator in the middle (on US cars). It may be a cat on vehicles in certain markets, such as Canada. Since you have not identified the country/region in your profile, I cannot be more specific. I agree with the note above, the technician may not be fully accurate in his diagnosis. It is rare to see multiple cat failures simultaneously without some outstanding cause. If it were me, I'd get a second opinion.

my cyls were slightly misfiring from the time i bought the car. Check engine never showed up and slight rough idle was never a concern until it got very bad. Can that cause cats to go faster than they should?

I live in Canada so I think i have the resonator?

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  • 1 month later...

I was wandering if anyone knows how many cat. converters GS400 has? I've been given different info from different sources. Also, since the car is 13 years old and has 300,000km on it i don't think its feasible to install OEM. Any suggestions/tips on aftermarket cats?

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I was amazed with your mileage at 300,000. I own a GS400, also 1998 and it runs great at 95,000 miles. Was wondering what other problems besides the catalytic converter you experienced through the years.

Good luck with the converter.

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  • 1 year later...

I have 230k on my 1998 and I keep it in top shape. My shop just changed out a bank 2 O2 sensor after seeing a P0430 code and found that sensor slow in responding. They said the next time the check engine light comes on with the P0430 code they will need to changeout the right cat at $1350 parts and labor.

I am wondering if I can just swap out the cats with the much cheaper after markets found at sites like autopartswarehouse.com ?

Just a side note: I have been looking at a replacement for this car, namely a 2006 GS300 and have driven two, each with over 80k miles on them. Owners of these obviously didn't keep up on maintenance and both cars were junk compared to my 98 gs400.

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  • 2 weeks later...

My GS 400 has 180,000 miles and I started getting occasional Check Engine warning lights

after the plugs were replaced at 120,000 miles. Had the problem on and off for about a

year and half and then it went away and came back about three years later. All times

it was I believe 430 indicating that one of the catalytic converters was bad. I have

never believed this reading. Every time I went to the dealer to get the warning light

shut off, the light did not come back on for a month, sometimes six months etc. If the

cat was bad, it would be back on almost immediatly.

I live in Maine where there is no emission check so on two occasions I went back to Virginia

and had an emissions check done on the car. In both cases, the emissions check came

back without any problem. Last time I had this done (about two months ago,) three hours

after the emission check came back as PASS, the check engine light came back on. It was

after I had driven in stop and go traffic for about two hours on a hot day. Emission check

was still PASS and dealer had no explanation.

I believe a plug occasionally misfires and causes something to trip the sensor and falsely

indicate that the Cat is damaged. Before going out to spend many hundreds on a new

cat, get an engine emission check and make sure the cat is really bad.

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The rep at the company who repairs my GS400 said that they have replaced cats with aftermarkets on Lexus's and Toyota's, and after that is done the check engine light eventually comes on again. He speculates that the aftermarket bolt-ons don't have the platinum level to make things work as original.

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  • 1 month later...

It's great to see others with 1998 vehicles and high mileage. I have a 1998 GS300 with 202,000 miles on it, purchased it as a certified used vehicle in 2001 and have never looked back. It runs like brand new, but I have invested a ton of money in the last few years on repairs and keeping it in tip-top condition.

All the engine seals, water pump, AC compressor, condenser, and now I have to do the bank 2 cat. To me, it is well worth it as many people think the car is only a few years old - nobody ever guesses it is actually 15 years now!!!

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Hello fellow Lexus owners, I am new to this site. I'm not sure if this is how I post a comment. Please let me know if there is a better way to do it, I could only think of responding to a post. Such as I did here. Thanks. Sinceerely, Marv

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Any aftermarket is fine. They are bolt in cats. You will need new gaskets and bolts/nuts. See attachment for diagram. There are two cats; bank 1 (cylinder 1-4) and bank 2 (cylinder 5-8).

TO Mr. Guy Telefunken, I have two questions to ask. The ballast went out on the right headlight on my 1999 GS400. Who do you recommend to contact to get a new ballast? Thank You. Sincerely, marv
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