I'm pretty sure the oxygen sensor voltage range is about 0.1 to 0.9 volts. Not sure the 3+ volt reading can be believed.
What does EQ_RAT mean?

You also mentioned a pending P0404. The RX300 diagnostics manual I use doesn't mention that code.

 

Old school oxygen sensors output a voltage from about .1v to .9v but the RX300 uses A/F sensors upstream. They actually output a current which has to be interpreted by the ECU and converted into a voltage. This voltage is usually around 3.3 to 3.6 volts and is not terribly useful by itself. Also, some scan tools don't properly interpret this data. This is where EQ_RAT (Equivalence ratio comes in). Equivalence ratio is the ratio of the actual air/fuel ratio to the stoichimetric ratio. It should be very close to 1. Higher than 1 is rich, lower than 1 is lean. I believe the Bank2 EQ_RAT reported as 1.997 is a typo by the original poster as the engine wouldn't even run if the equivalence ratio was 2x stochimetric.

 

Sounds like its working correctly.

 

Lex, Baetke, Max -

Thanks for helping coach me through this. In summary:

1. My fuel trim ratios are somewhat improved at 2000 RPMs (and improving slightly since air filter change);
2. I've added a new pending code (P0420);
3. My EQ_RATs are all ~.997 now;
4. My MAF is an off-brand, but new, and was presumably replaced by someone encountering the same problems.

Given Round 2 of all this info, how do you lean? If still the MAF, what would be the next culprit after the MAF?

 

We know that your idle rpm is correct, and at that idle you are letting much less air into the engine than the MAF is reporting. the error appears to persist at higher rpm. So I think you get the Denso MAF and put it in and see if it improves. Unless you know someone else with an RX and can just swap their MAF in your vehicle for a quick check.

 

I re-checked my notes on MAF performance and found the following...

At idle the MAF output should read between 3.3 and 4.7 g/sec.
At 2500 rpm (no load) the MAF output should read between 10.4 and 15.4 g/sec.

Not sure what to make of the P0420 at this stage. Doesn't seem consistent with the other symptoms.

I'm wondering if the previous owner maybe replaced the A/F sensors with non-OEM sensors, a definite NO-NO. In every case I have read, owners that have used non-OEM sensors of any kind on a Lexus have wound up replacing them with OEM.

Your EQ_RAT numbers look good. Maybe its time to reset the ECU memory and start from scratch. Fuel trim numbers must be brought into spec (LT + ST < 10%).

 

Good Idea!

 

It says here that running too rich can cause the P0420 code to trigger.

http://ricksfreeautorepairadvice.com...ix-code-p0420/

 

One of the best articles I've ever read on how the fuel system works. Definitely worth reading.

 

I ignored my system too lean codes for many months before I had to fix it prior to inspection. After doing the diagnosis I replaced the MAF and resolved the condition.
Shortly after fixing it I got a P0420. I think running rich for all that time may have fouled the cat.
I replaced it with a Walker cat and the P0420 did not return.

I captured live data from B1S1, B2S1, B1S2 at that time and it never exceeded 1 volt

Here's the graph

 

My research on the part # for my '02 RX300 had me buy a Denso 234-9009 O2 sensor,you used a Denso 234-4215. Are these compatible or is your model Lexus and/or year different.Anyone know if I do have the right sensor and what will happen if I install it and its wrong?Obvious performance with continued CEL?Thx,was ready to R/R and thought I'd double check the "how to" here and boy I may have saved myself some frustration.Thx for any and all info on the part #.

 

How about on line dealerships [Lexus/Toyota] and give them your vin number? Buying from unknown sellers may end up costing you more.

Salim

 

Thanks for your reply Salim,the part # on the new sensor is Denso 89467-48011,not sure how that translates to sellers claim part # of Denso 234-9009 or the DIY here stating to use Denso 234-4215?Probably will remove old sensor and see if I can make out the part # and call lexus parts for compatibility and cross refrencing....unless anyone here knows can save me some time with the R/R.
Its bank 1 sensor 2 for '02 RX300.
Thanks,
Paul

 

I'm pretty sure the Denso 234-9009 is sensor 2 - after the cat. It has the 2 bolt flange.

The Denso 234-4215 is a sensor 1 - before the cat. It has a threaded flange and screws in.

That is how I used them in my 2002 RX300 and they work fine. I just replaced one a week ago so I know the numbers are still good.

Google it. I got mine from Amazon. Good luck.

 

Reverse the part #'s