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Pete
Pete, Technician
Category: Lexus
Satisfied Customers: 24730
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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1994 lexus LS400 failed smog check 3x hc are to high. There

Customer Question

1994 lexus LS400 failed smog check 3x hc are to high. There is no check engine light on. I 've had oil change.replace PCV valve and intake air duct. At15mph HC is 97& 25mph HE IS 33. IS IT MY oxygen sensor?
Submitted: 2 months ago.
Category: Lexus
Expert:  Pete replied 2 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Make sure your engine air filter is o.k. and that there are no restrictions in the engine air flow through the filter housing to the engine.If this is o.k. and no codes are set the most common cause is the oxygen sensor nearest to the engine.I would replace both sensors as this model uses two sensors before the catalytic converter one for each side of the engine.I have seen these fail commonly in the past needing replaced for high HC issues.

One other common component is a faulty reading mass air flow sensor shown below.If this is dirty it can send false signals causing this issue.Usually you can purchase a can of mass air flow sensor spray cleaner from a local parts store and remove this sensor spraying off the sensor to clean it for it to read properly again.

https://www.dropbox.com/s/7gltwsbi01tr57i/air-09-20.gif?dl=0

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 2 months ago.
Here is some more info on my Lexus. In 10/2014 the EGR pipe was replaced or repaired. Is the O2 sensor on the left side or the right side in the engine
Customer: replied 2 months ago.
Here is some more info on my Lexus. In 10/2014 the EGR pipe was replaced or repaired. Is the O2 sensor on the left side or the right side in the engine?
Expert:  Pete replied 2 months ago.

I apologize for the delay as an emergency had come up.

According to a diagram I have located it looks like both pre catalytic converter oxygen sensors are on the drivers side but it may be this diagram is incomplete and you may have one on each side of the engine near the engine.

https://www.dropbox.com/s/3iftknr30x8bro8/oxy-09-25.gif?dl=0

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 2 months ago.
What does it mean when it says Upstream O2 sensor and downstream
Expert:  Pete replied 2 months ago.

Upstream is before the catalytic converter and down stream is after the catalytic converter.

Thanks Pete

Expert:  Pete replied 2 months ago.

Hello I am just checking in with you to see if there is anything else I can help with here?

Let me know,thanks Pete.

Customer: replied 2 months ago.
There are two O2 sensors on the driver side can you let me know what sensor is parallel to the O2 sensor on the left side. And do you have any other diagrams the location of the O2 sensors
Expert:  Pete replied 2 months ago.

In this diagram below you will see the Heated oxygen sensors bank 1 sensor 2 and bank 2 sensor 2.It is not these 2 sensors but instead the others that are in front of these two closest to the engine.

https://www.dropbox.com/s/am3s5ho0nteu4us/ex-10-03.gif?dl=0

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

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