ljb1955

Hi, My 99 ES300 has a CEL light. I have an AutoTap scanner and read the code P0420 which is a catalytic efficiency error for bank 1. I am trying to determine if the cat is really bad or if it is an air/fuel sensor problem. I am still a novice with the AutoTap scanner but I have attached the sensor outputs. The one that caught my eye is the "short term fuel trim from bank 1 sensor 2" which is at 99%. I'm pretty sure sensor 2 is the one after the cat. Can someone familiar with this give me some advice?

thanks

VVT-i

Welcome to CL. I don't know your Autotap can read the O2 waveform or not, but that what you need to look for. On the 1995-2001 LS400 with V-8 engine if the code shows P0420 or P0430 it's pretty much a bad cat. But on the 99 ES is something that you will need to look deep into before put in a thousand dollars catalys convertor.

ljb1955

Thanks for the reply WT-i. The AutoTap does display O2 waveforms so I'll try and capture them as an attachment. My ES300 still has under 80K so the cat will be covered under warranty. I'm just trying to make sure it is the cat thats bad before I take it to the dealer.

koolaidman

its kinda hard to diag with out a scanner but its possible. if u can get voltage readings from the sensor watch its change .2 to .9v. if it changes drasticly like that
u need a new cat

if it stays at say .3 to .4 -.5v almost a flatline
cat is good

ljb1955

Ok, I captured the waveform from sensor 2 with my AutoTap. I did this at 2500 rpm. Look at the attachment. Does this seem normal? I think this means the catalyst is bad.

koolaidman

how bout a waveform at idle. in closed loop

ljb1955

OK, here is the attachment showing sensor 2 in a closed loop condition at idle. Also, I finally crawled under the car to look at the sensor and check for exhaust leaks. The sensor looked ok and I could not detect any leaks. I was wondering where the connector for sensor 2 is located in the car? Is it under the seat? It is a 99 ES300.

Thanks again for your replies
Len

koolaidman

just replace the sensor. its getting lazy

ljb1955

thanks for the replies Koolaidman, I'll look into getting another O2 sensor.