On My 2007 IS250 A few months ago I got the CEL along with the Check VSC. I read the code with a code reader and it read as follows:

Stored Code: P0174 System too lean bank 2
Pending Code: P0171 System too lean bank 1

Prior to this happening about 1100km before I changed the spark plugs, changed the gaskets with new genuine lexus gaskets and also replaced TB gasket. I checked all the connections and checked that i tightened all screws around the gaskets.

My car has way over 100k miles on it so I thought I would change both upstream O2 sensors. So few weeks ago I changed both sensors with new Denso replacements. Drove the car and it drove silky smooth almost like a new car. I also took the opportunity to change the PCV valve with new Genuine valve. However, about an hour after driving the CEL came back on. Read the codes and it read:

Stored Codes: P2195 - O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 1

Pending Codes:
P2195 - O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 1
P2197 - O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 1

So I cleared the codes. I checked connections and the breather pipe from intake to engine wasn't tight it came off easily with a pull. So I tightened it up and cleared the codes. I did a return trip of almost 200km nothing came up then the next day the CEL came back up this time reading:

Stored: P2197 - O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 1
Pending: P2197 - O2 Sensor Signal Biased/Stuck Lean Bank 2 Sensor 1

At first I thought maybe the O2 sensor on Bank 1 was faulty but it seems to be alternating between the two banks. Any ideas on what I can do to try and figure this problem out?

 

I'm not sure about it but have you tried a new mass airflow sensor

 

My Mass AirFlow sensor was changed a few years ago. I may have a second-hand one lying around somewhere that I can try.

 

I have a feeling that the sensors purchased of eBay were fake replicas. The packaging was proper Denso, the plugs looked good quality they were etched with the Denso logo etc. The seller on eBay mainly seems to sell these types of sensors. The packaging had Japanese writing on it. A pic of it is below. Even if it was fake I thought it should at least work considering the seller has lots of good feedback. I did come across one negative feedback for the exact same sensors where the buyer said they were fake rubbish.

 

Try RockAuto.com. Never buy crital components from eBay.

 

Ebay once again America's money Pitt. Selling fake everything. Clones. Why you think the price is reasonable.. If it were real you wouldent even want to buy it. Thats the problem, you get what you pay for. I dont blame you, i blame ebay and all the sellers that just make stuff in the garage and then put it up online. I admire the talent but refurbs come on.

 

The big cost I've found is getting the OEM connector for ease of install. I.E matches OEM for gromets, length, jacketing, connector ect.

The Denso sensor is one cost. It being a drop in install usually triples if not quadruples the cost. But that means butt connectors, sealing type shrink tubing, and all that jazz plus time and tools to do it right.