EPayne42

Hello ...1999 ES300 is throwing the dreaded P0420 and P0420 pd codes. I had an axle seal that was leaking ATF. It dripped (and burned off) on the exhuast ...then the codes came. Was thinking the heat generated by the ATF burning before the cat caused the system to read hotter exhaust temp on the entry side of the cat. The leak is fixed, but still getting the codes. I cleared them a couple times. They pop up after about 30mins of driving.

I know these codes have been discussed at length, but wanted to start a new thread as my leak situation may have added a new twist. The advice I read was start with swapping Sensor 1 Bank 1 (near firewall), but most likey I have a bad cat.

Any advice/personal experience is greatly appreciated.

ES300NZ

Trouble Code - P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There are two o2 sensors in the system, one before the cat, one after. (there's also a a/f sensor).

The difference between the sensors o2 sensors is how the system comes up with this code. (or rather the lack off)

You can either replace the CAT (which is likely the issue), or both o2 sensors on that bank. Good o2 sensors are always a wise investment for fuel injected car, as they form the very basis of the electronic fuel management system. But, you can also do nothing. It's not a series code, you can safely ignore it.

EPayne42

Thank you sir. I will start with the o2 sensors. They're not cheap as you know, but obviously easier to swap than a cat.

Any recommendations on a replacement cat? I've seen a Bosal cat online. As I recall, Bosal is a reputable brand.

Wht95scort

Before condemning a bad cat you need to make sure you have no exhaust leaks that could be drawing in extra oxygen before the O2 sensor. Typically a smoke test is used for this. If no leaks are found you have a bad cat. The O2 sensors job is to detect well oxygen. Too much it knows hey this cat isn't doing its job and a code is set. It also will think the car is running too lean and will start to add fuel giving you a rich condition and causing bad gas milage as well could damage the O2 sensor. Look for leaks first.

EPayne42

Yep... we're seeing the fuel economy drop. I'll do the leak test around the headers and y-pipe. I may try swapping that bank 1 sensor 1 o2.

PFB

Watch this YouTube video. It will help you determine if your Cat converter is functioning correctly or if ts defective. It will also help you diagnose your P0420 code.

A must viewing.

Phil


http://www.youtube.com/watch?v=9VZ5K...e_gdata_player

EPayne42

Thanks Phil! I need to upgrade my scanner