So I’m a new 07’ gs350 owner. Recently got these codes. I’ve been searching the forums for things you guys have done to fix issue. I don’t think the cats are bad. I’m going to check for exhaust leaks. But if all else fails I will do the spacer trick. Don’t wanna spend the $ on replacing cats. Help please

 

My experience has shown with Toyota/Lexus, the codes are usually independent of the cats being bad. Your suspicion may be completely correct. Even small degradations in efficiency will trigger the code, but the car test completely fine via a genuine “sniff” test for NOx and pollutants.

Ways they code can be fixed:
- Sometimes, just bad sensors. Most likely though, not.
- Spacers/non-foulers. Not always successful, but sometimes.
- Fix any air leaks in exhaust, and this car is in fact known to develop them. Removing the heat shields and addressing that may take care of it for you.
- Last resort, and cheap and relatively easy, is to wire in an emulator. $6 to $10 bucks and permanent.

There is no loss of performance or efficiency on any of these, the back sensors don’t influence ignition performance at all, they only monitor cats. Another really bad issue is that the code disables stability control, which is both incredibly stupid and a safety risk. IMO, fixing the code as quick as possible is a smart safety move.

I hope this helps you categorize/prioritize what to do. It’s a really confusing issue and frustrating, I know. But with the right info you can solve it and short of new cats in any scenario, short of the cat actually being physically broken and choking air flow.

 

Start 1st with looking for exhaust leaks. Repair if found.

Then check to see whether you have carbon build-up. Run Chevron Techron injector cleaner thru a few tanks of high quality gas. Make sure you are running with Lexus/Toyota OEM spark plugs, not counterfeits. Clean your MAF.

Since both banks are throwing codes, you have a system wide problem, most likely not the downstream sensors.

 

I am curious and have the same codes. What did you find?

 

so driver side I had a clear exhaust leak that was patched. Cleared my 0420 code need to find exhaust leak on passenger side. But I’m pretty sure that’s it

 

Exhaust leak on the Y pipe between the cats where the O2 sensor is mounted caused my codes. Fixed the exhaust and they are gone.

 

Thanks, I had a leak at the flex pipe for sometime that I ignored - well behind the downstream sensors on my ES 300. I am thinking these are not the cause. These are the only codes present.

Separately, my LTFT for both banks rises from normal levels at idle to the 30%+ level -- This is my source of immediate concern.

MAF reads right on 1gr/cylinder/1,000 rpm, so I consider it good.

I am thinking:

My trims are ok at idle so I am thinking that rules out vacuum leak and I certainly do not hear one.

This kind of laves me with low fuel pressure that the trims are trying to make up for?