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2000 Lexus LS 400 help with oxygen sensor reading

Tiny
QEWANI
  • MEMBER
  • 2000 LEXUS LS 400
Computer problem
2000 Lexus LS 400 V8 Two Wheel Drive Automatic
Need help with O2 sensor readings.
I have LS400 2000 model which has 4 Oxygen Sensors.
I think that I may have some problem in my O2 sensors.
if you guys could check this readings and help me with this issue & tell me if these sensors are either functioning correctly or not.
These are readings of O2 sensor back finally on idle without acceleration.
I do not have any DTC
the only problem is that
fuel mileage is low which is 19 - 20 MPG on highway compared with other LS400 owners who get 24-30 MPG on highway.
I have changed spark plugs, cleaned engine air filter. But I think it may be because of these O2 sensors.

Bank 1 sensor 2 readings are not similar to Bank 2 sensor 2 readings, does this means that I had to replace the sensor.

I don't know about these readings, could you tell me in case if any of these readings are wrong.
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Wednesday, September 22nd, 2010 AT 10:30 AM

15 Replies

Tiny
BLACKOP555
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Is there a way for you to get bank 1 sesnor 2. And short fuel trim bank 1 over top of eachother.

And the same with bank 2 sensor 2 and short term fuel bank 2 over top of eachother like you did with o2 sensor 1 and 2 on each bank?
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Monday, September 27th, 2010 AT 9:18 PM
Tiny
BLACKOP555
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Also can you get more info to show up on the graph from idle to acceleration and then let go back to idle. About maybe 5 seconds idle to accel then back to idle. That would be great

would like to see the o2's on eachother. Then each bank o2 sensor and their fuel trims.

Too inconclusive right now since I dont have the fuel trims with the o2 sensors to see whats going on right now. If you cant get any more info I can give you a good guess but with that little info ill be a lot more precise
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Monday, September 27th, 2010 AT 9:20 PM
Tiny
BLACKOP555
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Last thing is switch the o2 sensors around and see if the graphs change with them or if the different o2 from the other bank still shows that big flatline on the bottom when your hit the gas like that. Can you get a graph of the fuel trims and the bank 2 sensors when you hit the gas to the floor for a split second?
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Tuesday, September 28th, 2010 AT 10:44 PM
Tiny
QEWANI
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I did not switch the o2 sensors around yet. If you want me to do this inform me.

This is the graph of the fuel trims and the bank 2 sensors when I hit the gas to the floor for a split second.
This is the graph of the fuel trims and the bank 1 sensors when I hit the gas to the floor for a split second.
Inform me if you need any other/extra readings.
Thanks.
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Wednesday, September 29th, 2010 AT 3:20 PM
Tiny
BLACKOP555
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Looks like your having a issue with lack of fuel. Maybe dirty injectors or low fuel pressure. When you hit throttle they shoudl show rich but instead they are showing lean.

Your long terms are pretty high indicating adding more fuel which could result from a bad fuel pump or dirty injectors.

Reset the KAM and go from there. After its reset re run it and pay attentinon.

If the shorts and long terms start to raise right away bring vehicle off of idle and see if the fuel trims start to come back down untill it idles again. If so its a vaccuum leak.

If not it could be a dirty maf, plugged injectors, or low fuel pressure
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Wednesday, September 29th, 2010 AT 10:25 PM
Tiny
QEWANI
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From your previous post I could not understand this sentence
>>
if the shorts and long terms start to raise right away bring vehicle off of idle and see if the fuel trims start to come back down until it idles again.
<<

Can you explain more how to preform this?

I want to tell you that there is small crack on the hose called "PS Air Hose"
Could this be the vacuum leak?
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Thursday, September 30th, 2010 AT 12:16 PM
Tiny
BLACKOP555
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If short and long term fuel trim raise up as in leave 0 up to 5, 6, 7 8 percent etc and keep raising raise vehicle off of idle and see if the fuel trims drop back down to 0-5 percent
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Friday, October 1st, 2010 AT 12:38 PM
Tiny
QEWANI
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I had reset the KAM and run the car and monitored STFT reading which were between 0% to -3% and LTFT reading were 12%. Both reading direct came with these values without any start from 0, 1, 2, . Etc

I found that PCV valve is very dirty/may leaking and I think it may causing the lean problem on idle. I will clean or replace it and check the STFT/LTFT readings again.
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+1
Friday, October 1st, 2010 AT 3:07 PM
Tiny
QEWANI
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PCV hose was cracked and leaking on both of
intake manifold side and cylinder head side.

I used a tape and installed hose back. Cleared KAM and checked STFT/LTFT readings which came with these values
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Saturday, October 2nd, 2010 AT 7:50 AM
Tiny
BLACKOP555
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Glad to hear you found the problem.
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Saturday, October 2nd, 2010 AT 1:11 PM
Tiny
QEWANI
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Are posted values of STFT/LTFT are fine now?
Thanks.
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Saturday, October 2nd, 2010 AT 3:52 PM
Tiny
BLACKOP555
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They aint the best but they are within spec. As long as they are bellow 15%
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Saturday, October 2nd, 2010 AT 5:36 PM
Tiny
QEWANI
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What are is the best reading of fuel trims?
And how could I get those reading?

Are O2 sensors of my car are functioning correctly or they are slow? Do I need to replace any O2 sensor to get better fuel economy.

Thanks.
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Sunday, October 3rd, 2010 AT 4:16 PM
Tiny
BLACKOP555
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The one that is not bouncing up and down the voltages as fast seems a bit slow. I would suggest switchign the two and seeing if the slowness goes with it. If it does sensors bad. If not then its bank related.
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Monday, October 4th, 2010 AT 8:51 PM
Tiny
QEWANI
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Here is an updated graph with O2 sensors bank1/bank2 readings
which sensor seems to be slow?
Post-cat O2 sensor readings on both banks is high, is this normal?

Thanks.
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Tuesday, October 5th, 2010 AT 2:29 PM

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