Samuel77

Yesterday the check engine light and the VSC light came on. I pulled the codes and got

P1150 A/F Sensor Circuit Range/ Performance Malfunction Bank 2 Sensor 1

Does this mean that the A/F sensor at the front of the engine needs to be replaced
( Front part of the intake)? Also i disconnected the battery a day before this happened, dont know if thats relevant.

GS4_Fiend

iTrader: (22)

Thats correct

hypervish

Yup, here's the sensor you need:

Samuel77

Thank you very much.

hypervish

Just an FYI: It's the exhaust manifold.

kerno

I recently bought a 1999 RX300 and noticed that the pre-cat O-2 sensor is new and the post cat O-2 sensor is original. Is it normal for only the pre-cat sensor to go? I figure if one went bad in 93,000 miles, I probably ought to do the other one as well. My understanding is that the pre cat sensor measures the mixture going into the primary catalytic converter and the post cat sensor sniffs the exhaust out of the cat to make sure the cat is working properly If the post cat sensor is lazy, it may have an effect on gas mileage..

Opinions?

code58

You have 2 sensors up front and one in the rear. The front sensors are actually A/F ratio sensors, commonly called oxy. sensors by many people and parts books so it is confusing, to say the least. The front ones (referred to as B1S1 and B2S1) Air/ Fuel Ratio Sensors are on the front manifold where it comes out of the engine and the rear (A/F ratio sensor) at the same place, on the exhaust manifold where it comes out of the engine. The rear (oxygen sensor, not A/F ratio sensor) is, as you have noted, behind the cat. conv. to test how the cat is doing. The rear one rarely ever goes bad. The front ones (both the same part number) are the ones that do go bad but normally after 90-100K mi. or so. To get to the rear A/F ratio sensor you have to jack the car up and get under it or have it on a lift. There are plenty of write-ups on it as well as pictures (with a search).

hypervish

Mine lasted till 160k miles, at which point it set a P0420 code. After I replaced the sensor, the code never returned.

Samuel77

It seems like I have recently replaced this very sensor but it might have been defective (I doubt it because lexus did it themselves) But could I use this sensor

code58

Samuel,
You've probably long since dealt with the issue by now, but since I see that you didn't get an answer, I'll give you one. I was assured that the universal sensor would work on my DIL's RX, and it didn't. (this was a DENSO part) It takes A/F ratio sensors and that universal part is an Oxygen sensor. They are 2 VERY much different parts, though they look very much alike. The part you need should be this one:
If the Lexus dealer replaced the same sensor recently, I'd return to them as it should be under warranty. The sensors should last any where from 75-150K mi.

Iluvlexus

Just finished replacing the air-mix servo in record time (I finally bit the bullet and put a new one in after 2 failed repair jobs) and all was well until the VSC and check engine light came on. My 2001 has 145k and runs beautifully. Of note is that I disconnected the battery to do this project as I didn't want the light to burn while the doors were open. This seems like a common theme for this error code. Wondering why and what to do. Not sure why disconnecting the battery would make the O2 sensor go bad???

Thanks, Scott

carguy07

I'm sure the battery did not make the O2 sensor go bad. Try disconecting again and see if it comes back.

Iluvlexus

Happy to say I disconnected the battery again to reset the computer and no check engine light after 100 miles. Whew! Do have 145K on the original O2 sensors. How much longer can I expect them to last?

Lexmex

After 100K is around the area where I have seen them have issues, I believe right around your mileage is where I had to replace mine.