milellie11

iTrader: (5)

Well, after the general consensus that i needed my Cats replaced because of code P0420 (Catalyst Efficiency Below Threshold Bank 1) which the Lexus dealership and independent shop told me, i had 2 OEM Lexus Cats put on by a muffler shop with new OEM gaskets. Ecu was reset. This was about 2 or 3 weeks ago.

Yesterday i'm driving around, light pops back on, get the code scanned and its code P0420 (Catalyst Efficiency Below Threshold Bank 1)! So i guess my Cats were never the problem Please tell me where to go from this and how i can resolve this. I am still noticing a loss of power so obviously the issue is still not resolved.

I know you guys told me before to replace all the oxygen sensors before i spend money on Cats, but a few people told me that if it was an oxygen sensor, it would be a different code and most likely it was the Cats. So, i didn't feel like throwing oxygen sensors at the car and still needing to replaced the Cats but it looks like i'm screwed regardless. Please help!!!

GSteg

iTrader: (15)

A bad sensor can still throw the same code if it's not reading incorrectly.

EDIT: correctly, not incorrectly.

milellie11

iTrader: (5)

Can a bad sensor cause power loss?

Also, how do i know the correct sensor to buy? The one on bank 1?

GSteg

iTrader: (15)

Yes a bad sensor can cause power loss if it's signaling the ECU inaccurate information.

The sensor that's signaling the code is on the driver side. It's located after the catalytic converter. You can have a shop monitor the sensor's activity to see whether they're working or not.

GS4_Fiend

iTrader: (22)

Time to change those O2 sensors. I dont understand why the mechanics got scanners and dont make good use of it. They can actually monitor the O2 sensors to see if the cat is bad or not.

milellie11

iTrader: (5)

Ok thanks. Final question: I just ordered this from amazon.com Denso part No. 234-4623 Oxygen Sensor Post Cat Left.

Was that correct and the only one i need?

GSteg

iTrader: (15)

I don't know to be honest. Not sure if there were any changes to the sensors between the years and the model.

sam430

iTrader: (10)

I had the same issue... my o2 wires were ripped... I had to to pull it up from the top along the transmission line (v8) and repaired it.

ricanrolla

Bank 1 is the passenger side down stream (after cat) oxygen sensor. You can get it online for $109 @ auto zone.

milellie11

iTrader: (5)

You sure? I was told that bank 1 is drivers side?

RLGS300

I had the same problem as you however i postponed replacing the cats, then a few weeks later after I cleared the memory, a code for the passenger side sensor came up..

ThomasGS4

iTrader: (19)

Bank 1 IS the driver's side.

sakataj

iTrader: (182)

while were on this....u can get them on amazon WITH the factory plugs for like $55-$70 bucks

oki_boy

iTrader: (6)

https://www.clublexus.com/forums/gs-...-seonsors.html

https://www.clublexus.com/forums/per...placement.html

https://www.clublexus.com/forums/gs-...n-sensors.html



the correct Denso part numbers are:

(1,2,3 precat) Bank 1 Sensor 1: 234-4048

(1,2,3 postcat) Bank 1 Sensor 2: 234-4626

(4,5,6 precat) Bank 2 Sensor 1: 234-4630

(4,5,6 postcat) Bank 2 Sensor 2: 234-4603


Got mine off amazon and they qualified for free 2 day shipping. Paid around $65 a piece and actually recieved them in 2 days.

milellie11

iTrader: (5)

Was this for a GS300? The part numbers are different for a GS430.