5t341th

iTrader: (16)

hi guys i have a 2000 GS300 with a CEL on. its at 107500 miles
its something about the catalyst being inefficient.
i've check the code and it turns out to be on "bank 1"

the CEL turned on after i got rear ended and i wonder what could have it broke/knocked loose.
it wasnt a hard collision but now the CEL is on

i've done a bit of searching, and people say to check/replace the oxygen sensor. if its on BANK 1, which should i be checking at? should i look at the first o2 sensor underneath the car?

also, how likely is it that the catalytic converter is bad?

thanks for any help

mitsuguy

iTrader: (2)

I would say 99% of the time when that code comes up on any car, that the catalytic converter is bad... possibly that rear end collision knocked some of the honeycomb material in it loose, who knows...

there are really two possibilities - one is that one or both o2 sensors on that bank are bad, however that is unlikely, as that would typically throw a code for the o2 sensor as well... about the only time it could be an o2 sensor causing the Catalyst low efficiency code is if the o2 sensor is just inaccurate, meaning it reads within normal parameters, but it read wrong... most o2 sensors do not fail that way - either the heating element wears out or they stop responding completely...

from identifix:
Customer Concern:
Trouble code P0420.
Tests/Procedures:
1. Monitor the front and rear oxygen sensors while driving the vehicle at approximately 55 MPH.

2. Monitor the fuel trims for being normal at 55 MPH.

3. Check the inlet to outlet temperature on the catalytic converter. Generally the rear should be 50 degrees or more hotter.
Potential Causes:
Catalytic Converter
Malfunctioning Oxygen (02) Sensor
Tech Tips:
It is possible to save the catalytic converter by grounding one spark plug wire and running the engine at 2500 RPMS for 2-3 minutes. Raising the temperature of the catalytic converter can sometimes bring them back into good operating condition. Always replace the front oxygen sensor when a code P0420 has been set.

here's a similar vehicle:
1999 Lexus GS300 3.0L
Installed both front and rear O2 sensors for bank 1, front O2 pattern was very erratic, would go high and low for extended period then back to normal,rear mimmicked front fairly close. Vehicle with 151K. Informed customer still possiblity of bad Catalyst.

there is one note in here, and I vaguely recall one vehicle with this problem and a p0420 - the exhaust manifold was cracked... replacing the exhaust manifold fixed that one, so, might also check for any exhaust leaks from the exhaust manifold to just past the cat...

5t341th

iTrader: (16)

thanks for the info. i will check the problems out once spring break is over

wolverine

iTrader: (9)

bank 1 is on the same side as cylinder number 1. since you have a straight 6, and not a v8, it would be the first one.

sam430

iTrader: (10)

I have the same code. It comes on and off by itself. I have the 8 and also a generic o2 sensor on bank1 #1.

"Tech Tips:
It is possible to save the catalytic converter by grounding one spark plug wire and running the engine at 2500 RPMS for 2-3 minutes. Raising the temperature of the catalytic converter can sometimes bring them back into good operating condition. Always replace the front oxygen sensor when a code P0420 has been set. "

How do you ground? remove the sparkplug and ground it?

mitsuguy

iTrader: (2)

don't remove the spark plug, just pull the spark plug wire and let it jump to ground... this means that one bank will be throwing in all kinds of unburnt fuel... that fuel gets caught in the cat and will sometimes reignite / burn... this causes way high temperatures in the cat and will sometimes burn off whatever has contaminated it...

or it might not help at all...

sam430

iTrader: (10)

Makes sense. Thanks!

Percy

My GS400 is throwing out PO420 and PO430 codes. Intermittent. Sometimes the CEL light stays on for a while, then disappears. Then reappears after a long while.

Ideas?

mitsuguy

iTrader: (2)

both codes come on at the same time and stay on together?

usually only one cat goes bad at a time, those codes show both sides... although odd, not unheard of... you could have a leaky exhaust manifold gasket causing both sides to return those codes, or also a exhaust leak just after the y-pipe...

if no leaks found, then most likely course of action will be catalytic converter replacement... you might try some of the tips above first though...

Spencerfg

Replacing manifold gaskets solved the same problem in my 2001 GS430. My usual service center, the local Toyota dealer, had insisted that the both catalytic converters needed to be replaced and quoted me about $3K (about 90,000 miles at the time). I didn't believe this was likely so I sought a second opinion and had the problem solved at 1/10 the cost.

Jan33

Hello, can you be more specific which manifold gaskets you have changed? There are few of them. Many thanks. Best Regards, Jan

mitsuguy

iTrader: (2)

Most common would be the gasket from manifold to the head.

You wouldn't want to guess though - listen for an exhaust leak and try to pinpoint it first.

lexusisgs

I have gs 450h hybrid 2008 and had same issue.
First time was leak on the gasket where are flanges under car close to O2 sensors.I ahd replaced both O ring gaskets on both sides. It was ok for about year or so now I have same intermitten P0430 and P0420 but I have to use scan tool to reset that code and it will be ok for couple days after sampling is done and will pop up again .I have checked again around flanges but couldnot pin point leak.
How many O2 sensors I have on this GS450H and which one is BANK 1 and which one is BANK2?


thanx