racerxxv

So. just bought this. got a great deal because the VSC TRAC, VSC OFF, and Chk engine lights are all on. Lexus told prior owner he needed cats and it would be $2700.

vehicle runs great. Gas Mileage is 14-16, about what I expected.

2004 GX470 with 85K miles.

I'm thinking cats are fine, this has to be 02 sensor issue.

plug in my blue tooth OBD code reader and fire up Torque App on the tablet.

showing codes:

PO420 Bank1
and
PO430 Bank2

I go in and look at the voltage coming off the O2 sensors.

Bank1 sensor 1 shows a nice lambda curve between .07-.74v
Bank2 sensor 2 shows a flat line.07-.11v

Bank2 sensor 1 shows the same nice lambda curve between .05-.74v
Bank2 sensor 2 shows the same flat line .09-.13v

Which has me a bit baffled.

Do I have 2 bad sensors? Which 2?

seems odd that both sensors would go at the same time...

In reading and searching the forums it seems that most folks are replacing their sensor 1. Very few reporting sensor 2 failing.

Does anyone know what voltage range the GX ECU is looking for from these sensors?

Is it even the O2 sensors? I've heard of folks replacing the gas cap because the seal wore out...

Or should I look at the MAF sensor?

Thoughts?

YoshiMan

Did it say if it was the sensors before or after the cats? I agree it's very unlikely that the cats are bad, especially on a Lexus with that few miles on it.... unless they drove to a foreign country and put leaded gas in it or something!

racerxxv

Hey Yoshi,

The code doesn't specify sensor1 (upstream) or Sensor 2 (downstream). which is part of why I'm confused.

The fact that it's running good also leads me to believe the cats are fine.

And looking at the voltages coming off the O2 sensors... I'm thinking they are ok too.

Just ordered a new gas cap from RockAuto. For $7 bucks...it's worth a shot.