Neutra in '98 LS400 Fuel with P0420

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VA
My 1998 Lexus LS400 has been throwing a P0420 code for the last few months. I used my BlueDriver and verify and erase. Car runs fine with 290K on it. Suddenly I had an epiphany! Why not pour some Schaeffer Neutra into the gas tank and see if it would make any difference. I did and have driven 3 days and 240 miles and no more CEL. Normally it would come back on after and hour or so driving. Very interesting. Now it may come back tomorrow but Trav has helped me get a back up plan for less than $10. Please don't fuss at me Trav. had to get a SS one. LOL
 

MolaKule

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I would try a can of Berryman's B12 and a bottle of Techron or other PEA additive. I have had CAT sensors that were on the edge go gaga in the wintertime and the above helped.
 
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Gebo

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Gotcha. I'll give it a week first and if it comes back I'll try the Berryman B12. I normally run the Amsoil PI about 3-4 times a year. Is it a PEA?
 
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Kuwait
One product I've had pretty good success with is Liqui Moly Catalytic-System Cleaner. I usually get two cans, feeding one complete can through a vacuum line and adding the other to the tank. If the cat is done for, obviously no additive will help, and they specifically mention manganese dioxide deposits cannot be removed using their product.
 

MolaKule

Staff member
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Originally Posted by Gebo
Gotcha. I'll give it a week first and if it comes back I'll try the Berryman B12. I normally run the Amsoil PI about 3-4 times a year. Is it a PEA?
Yes, Amsoil PI and Redline SI-1, Techron, Gumout Regane, etc., contain PEA's.
 
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California
Unless you're really burning oil or there's a bad injector or ignition system issue, it's hard to kill a Toyota cat. Your LS400 has a much more advanced engine management than the 1990-1997 cars did - COP ignition and SFI vs. two distributors/coils and batch-fire injection.
 
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Long Island, N.Y.
Originally Posted by MolaKule
I would try a can of Berryman's B12 and a bottle of Techron or other PEA additive.
MolaKule, is it preferred to run both the Berrymann's and the Techron at the same time or would it be better to run one first, then the other on the next fuel fill?
 
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Hudson, NH
Most late 90s, mid 2k Toyotas/Lexus burn some oil. Combined with high catalyst efficiency threshold programming, Toyotas are more prone to catalyst CEL's than others. Sometimes on the edge, a fuel system cleaner can work for a while. I tried them all on my high mileage Camry. Gumout multi system tuneup, a Seafoam/techron hybrid put the light out for the longest. But the CEL always came back. I have an idea what the $10 fix is, and its what I used. Never had a CEL again for over 100k.
 

Loi

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Location
Des Moines, IA
Most P0420 code is due to rear o2 sensor heating circuit not working properly or the sensor itself is bad. With 290k miles on the car I would replace the rear o2 sensor with a new unit. P0420 is very common with cars when going full catless exhaust as well.
 

Gebo

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Originally Posted by LeakySeals
thumbsup
Penetrol to the rescue! You still tracking?
 
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Chicago
I had the same code on my LS400 this summer. It was a exhaust gasket leak between the catalytic converter and piping. I used versachem exhaust weld, holding up great and no codes... Cost? $7
 

Gebo

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When I can get "my" car in the garage I'll check for any cracks and leaks. Thanks! Little chilly today.
 
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MA, Mittelfranken.de
Just look at the fuel trims to determine that, it will be adding a lot of fuel and probably throw a code for that too. A leak post cat may effect the rear o2 but you will see that in the voltage.
 
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25,166
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MA, Mittelfranken.de
Originally Posted by Loi
Most P0420 code is due to rear o2 sensor heating circuit not working properly or the sensor itself is bad. With 290k miles on the car I would replace the rear o2 sensor with a new unit. P0420 is very common with cars when going full catless exhaust as well.
Never replace a working rear o2 monitor, the slower and lazier it is the better. There are some cars that use the rear input to aid in fuel trims but they are not as common. With a new cat always replace both sensors. From Bosch..
Quote
Two-sensor lambda control combines the beneficial aspects of both upstream and downstream sensors Greater accuracy is achieved with two-sensor control. Here, a slower correction control loop is superimposed on the two-step or continuous-action lambda control described by means of an additional two-step lambda sensor. The voltage of the two-step sensor downstream of the catalytic converter is compared with a set point value (e.g. 600 mV) for this purpose. On this basis the control evaluates the deviations from the set point value and additionally alters additively the controlled rich or lean shift of the first control loop of a two-step control or the set point value of a continuous-action control.
 

Gebo

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My heart just broke....

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