In looking at the code and possible causes (the 3 bullets), I'm struggling to think why an exhaust leak is even a possibility as a cause.
O2 sensors measure oxygen, nothing else, hence the name...more oxygen in the exhaust and the car is running Lean, less oxygen, it's running Rich.
If you have an exhaust leak near an O2 sensor, this may introduce more oxygen for the sensor to detect.
Far be it from me to call into question the brilliant minds that author the repair manual, but the code says "Slow Response - Rich to Lean"...if you introduced more oxygen into the exhaust, it should be the opposite "Slow Response - Lean to Rich".
And notice in the code description is states this occurs after fuel cut...during fuel cut the oxygen volume in the exhaust is even greater, so if you add an exhaust leak to that, the O2 sensor should be reading Lean like crazy.

For those that had the dealer replace the exhaust gasket and it didn't fix the issue...no kidding, I couldn't see why it would.
The vehicles that had the issue, based on the code description you should have been decelerating when the CEL came on.
Fuel cut most commonly occurs during deceleration. When accelerating and cruising with constant throttle you shouldn't be going into fuel cut.

I don't know, just my two cents. Maybe I'm completely out to lunch here.

 

I think what you are saying makes sense. As for the code name, I don't know what it means by "Rich to lean" - is that the expected behavior or the problem?

 

More oxygen would give a lean reading, not a rich leaning. I think they have it right, rich to lean is more oxygen introduced. Going lean to rich would mean it's detecting more fuel.

 

The "Slow Response - Rich to Lean" means the sensor is taking longer than the ECU would expect to drop voltage after fuel cut. O2 sensors work on a scale of 0.1V (Max Lean) to 0.9 (Max Rich).
Rich to Lean is the expected behavior, but the Slow Response is the problem...it's taking too long to do the expected behavior.
You're correct that more oxygen is being introduced...the issue is the time that the sensor is taking to tell the ECU this information. The ECU is expecting an immediate change, but the sensor is taking it's sweet old time.
If you introduce more oxygen into the exhaust system then this would increase the time the sensor would take to move from a Lean to Rich reading...hence the alternate wording I suggested.
If you throw more oxygen at the sensor constantly it's never going to read Rich...but the ECU will also try to throw more fuel at the engine in an attempt to move the sensor reading. Eventually the ECU give up and throw a code that something is wrong.

 

Thanks, Joe Z. Yeah, really hoping this gasket replacement will resolve my issue but I guess only time will tell. It was love at first sight with the car so I'm remaining optimistic that Lexus gets to the bottom of this.

 

I believe Canada has better laws than the US in regards to recalls, I read somewhere that an issue has to be life-threatening for it to be a recall in the US. Just like the 2GR-FE engine on our Lexus/Toyota where the vvti and oil cooler rubber line would burst and leak engine oil which can ruin the engine. This was a TSB in the US but a recall in Canada.

 

I got my check engine light today. Around 100 miles on the car. Dropped it off at the dealership this evening and was told someone would be in touch tomorrow. Pretty ****ing annoyed. One of the biggest justifications for buying this car was Lexus reliability and here we are. I’ve owned multiple German cars and never had issues this early into ownership.

 

Sorry to read this. Hope the fix is simple.

 

I felt the same way. In fact, you simply cannot say that the IS500 is reliable at this point. Think about this: I will never be able to tell people, “I’ve NEVER had a problem with this car.” It’s a shame. These engines might be “bulletproof,” but the electronics and car as a whole are not immune to issues more than any other car manufacturer.

But go ahead people. Keep buying them and putting on your PPF and ceramic before you know if you have a lemon or not.

 

I have 70 miles or so since Sunday. I'm going to to call the dealer and ask them to expect me soon and order the gasket/sensor now so I don't have to wait around.

Think they'll tell me to pound sand?

 

have you been on the freeway yet?

 

Yep, prob 8 miles or so. Another 10 tomorrow. Nothing yet.

 

If you get the chance, try slowing or braking from about 70 to 50 on a curve/on ramp. That might trigger it.

 

Will do. That's something I haven't done yet is get into the brakes much.

 

Seems a bit pessimistic….