B1 S2 showed zero volts twice not good , fuel trims look stuck on bank 1 If it was my vehicle I change B1 S2. Short explanation of trims Short Term Fuel Trim (STFT) is what the engine computer is doing to the fuel mixture right now.

This value changes rapidly and can bounce around quite a bit depending on engine load, speed, temperature and other operating conditions).
Values normally range from negative 10 percent to positive 10 percent, though the readings may jump as much as 25 percent or more in either direction.

Long Term Fuel Trim (LTFT) is a longer term average of what the engine computer has been doing to balance the fuel mixture over a predetermined interval of time.
This value is a more accurate indicator of how the fuel mixture is being corrected to compensate for changes in the air/fuel ratio that are occurring inside the engine.

 

What's the rationale for changing B1S2 as a fix for P0171? I thought its main function was to measure catalytic converter efficiency.

These are the listed causes of P0171 and P0174

• Gas leakage on exhaust system
• Air intake (hose loose)
• Fuel line pressure
• Injector blockage
• Mass air flow meter
• Engine coolant temp. sensor
• A/F sensors (bank 1, 2 sensor 1)

Again since this all started after you replaced B1S1 you might want to consider swapping it with B2S1.
At least it wont cost anything.

 

@ maxsteel, your posted suggestions can absolutely cause those codes, can we agree that the problem is in bank one so we can eliminate components that would effect both banks? reading the data that was posted b1s2 shows no voltage, which is leading my thoughts to the sensor, also the miss fires were all in bank 1, P300, 301, 303, 305 the problem is def in that bank. @ Xavier56 do you have access to a lift? If you do double check all exhaust gaskets leading to the cats including exhaust manifold. try not to get the vehicle really hot it may be a cold joint leak also how long does it take for the CEL to illuminate please post freeze frame data. good luck.

 

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p300 p301 p303 p305 p171 directly from identifix
2000 Lexus RX300 3.0L, V6, USA*
test details confirmed fixes
Tests/Procedures: 1. 1. Monitor the fuel trims for bank 1 and bank 2. If bank 1 has really high fuel trim and bank 2 looks normal, suspect a faulty air fuel ratio sensor. If bank one fuel trim is really high, unplug the air fuel ratio sensor and see if the engine runs better when in open loop. This would be another indicator of a faulty air fuel ratio sensor.

2. If the fuel trims are both doing the same thing it is more likely that the mass air flow sensor is faulty. With a bad mass air flow sensor the fuel trim numbers usually look ok at idle but then start to increase as the vehicle is driven under load.




81 Confirmed fixes

• Air Fuel Ratio (AFR) Sensor
• Mass Air Flow (MAF) Sensor

• 39 - Air Fuel Ratio (AFR) Sensor
• 11 - Bank 1 Air/Fuel (A/F) Ratio Sensor
• 8 - Mass Air Flow (MAF) Sensor
• 4 - Spark Plug(s)
• 3 - Ignition Coil(s)
• 2 - Catalytic Converter(s)
• 1 - Knock Sensor(s)
• 1 - Spark Plug Wire(s)
• 1 - Exhaust Gas Recirculation (EGR) Valve
• 1 - Evaporative Emission (EVAP) System Hose(s)/Line(s)
• 1 - Intake Air Boot
• 1 - Exhaust Gas Recirculation (EGR) Vacuum Solenoid Valve (VSV)
• 1 - Timing Belt Tensioner
• 1 - Fuel Injector(s)
• 1 - Mass Air Flow (MAF) Sensor Intake Air Duct
• 1 - Bank 1 Air/Fuel (A/F) Ratio Sensor and Bank 2 Air/Fuel (A/F) Ratio Sensor
• 1 - Air Fuel Ratio (AFR) Sensor and Catalytic Converter(s)
• 1 - #3 Exhaust Valve
• 1 - Bank 1 Air/Fuel (A/F) Ratio Sensor and Mass Air Flow (MAF) Sensor and Throttle Body
• 1 - Ignition Coil(s) and Knock Sensor(s) and Mass Air Flow (MAF) Sensor and Spark Plug(s)

 

Despite being called "B1S2" it is not specific to B1. It is the oxygen sensor aft of the rear catalytic converter, so it applies to both B1 and B2. Its purpose is to determine if the cat is working. If it is the voltage should be very low. I do not know if his reader may be zero-ing very low values.

 

Ok was away for few days - Now back at it - Today Removed Bank 1 Sensor 1 behind firewall from bottom and installed another New Sensor - No change - STFT B1 started out at 0%

And went to 19.5% shortly - (Likes that 19.5 % number) - So went under the car and disconnected the Bank 1 Sensor 1 (as someone suggested) - Started Car and Ran -

STFT B1 still at 19.5% with no A/F Sensor on Bank 1

With Sensor Disconnected completely - What does that tell Us????

Direction next???

Answers to this list sent to me

These are the listed causes of P0171 and P0174

• Gas leakage on exhaust system - Do not see or hear any exhaust leaks
• Air intake (hose loose) - Removed , inspected and reinstalled and did smoke test do not see any leaks
• Fuel line pressure - I figure would effect both Banks - Correct??
• Injector blockage - Not sure how do check this one - Bank 1 is hard to work on so last resort??
• Mass air flow meter - Installed New one
• Engine coolant temp. sensor - Engine Temp working on Dash and on Code Reader - unless there is one do not know about
• A/F sensors (bank 1, 2 sensor 1) - Changed Bank 1 Sensor 1 Twice

 

So went under the car and disconnected the Bank 1 Sensor 1 (as someone suggested) - Started Car and Ran -

STFT B1 still at 19.5% with no A/F Sensor on Bank 1

With Sensor Disconnected completely - What does that tell Us????

Direction next???

Answers to this list sent to me

 

Any updates?

 

Ok changed the Bank 1 Sensor 1 again with another new one no change. When I was doing a smoke test on the Evap system I thought I heard a click once some place. (during test did not find any leaks). So ran car at idle and the Bank 1 St Trim was acting normal like Bank 2. First time seen that since started this. So Ok must be a switching valve. Drove car and Bank 1 St trim went back to +19.5 %. Removed switch valve it worked OK could not find any issues. Removed other two Switching valves and tested they were Ok. Pressured the switch valve and it did not go to like before with OK St Trim. So do not have a clue why it acted good for a short time.

So ordered a cone so can back pressure smoke exhaust system, ordered a Evap connector to do smoke test on Evap from the Lexus test port. Ordered a fuel rail bolt that going to have drilled and tapped so can do pressure test on fuel system right from fuel rail.

If you run the car and what Bank 1 St Trim it goes to the +19.5% if you hit accelerator it goes to 0% which tells me a Air leak some place. I tried the Carb Cleaner spray again all over and cannot find a air leak.

So right now still do not know what causing this still and cannot find any leak or issue. Open to any ideas

Thanks

 

Forgot this - I changed the 02 Sensor after the Catalytic Converter too with a New One. Seen no change.

 

Was this issue ever resolved?

 

Hello - yes the issue was Fixed and it was from a Fake O2 Sensor that was the issue after finding the issue of a bad sensor first.

I purchase two different ones and both were Fakes - the one From Local Part Store did the trick.

Now I am still dealing with a P0440 code. Cannot find why keeps coming up.

Changed Gas Cap - Canister under car. Checked Solenoids under engine cover - did smoke test and nothing found.

So still a Good Guess what it can be

Ideas??

 

So initially you did not use a Denso?

 

Can I ask where you bought the fake O2 sensors? .So that others (and I) can hopefully avoid them?
Thanks.

 

They were Fake Denso's they looked just like Exact Real ones and the boxes looked real too.

If you compare Real one to Fake you could not tell right away. It was etched and everything,

Very Very Good Fakes.

There was a slight change at the very end were wires came out. Someone else said from data must be fake.

So purchase one locally.

The Fakes were Purchase on Ebay from two completely different sellers

Once I told sellers they were Fake they Refunded Money right away so they knew.

They did want me to complain to Ebay.