TominPT

Decided to do a smog sensor cleaning today, knowing that the PO probably never did it. Figured it was long long overdue and it was.

Anyways, the climate control system will go into recirculation mode if it senses the outside air is too dusty or polluted and includes a sensor to tell it what to do. The sensor is located in a black rectangular box right behind the drivers side horn immediately in front of the radiator. First, remove the 12mm bolt holding the sensor to the radiator bracket, then CAREFULLY disconnect the plug to the sensor. Remove the back cover by lifting up on the 4 tabs and you expose the small fibrous filter element that protects the small sensor in there. If your car is like mine ('98, 150,000 miles) its probably filthy in there and the fiber clogged with dust and dirt. Remove it and give it a good bath (I just used soapy water) squeeze it dry blotting with a paper towel and reinstall,

The horn is in the way to remove the back cover. Leave the horn alone, just remove the sensor via the 12 mm bolt. There is no nut for the bolt. the housing includes a little tab that goes in the small hole on the radiator bracket. I just love these little details in the LS400. so much thought went into EVERYTHING.

While you are in there, lube the hood release mechanism on the hood and on the radiator bracket.

CLLEXUSS

This was a good subject matter one that gets easily overlooked. I documented my experience with images on my 2000 Model. All I needed was a 10mm wrench for mine and removed the one bolt, disconnected the electrical connector and removed the sensor unit so I could work on it away from the car. I believe it's actually called a "Air Quality Sensor Thermistor". Denso 176900-0010. This is mine with over 150K miles on car. Before and after images. It cleaned up nice, used soapy water for the filter and let it dry in the sun before re-install. I used an old toothbrush and a Q-Tip to clean out the inside of the unit. It worked very well and didn't take much time. Thank you for starting this thread, it's a good thread. Maybe when you get the time, re-name the title of this thread to; "Air Quality Sensor Thermistor". It's certainly a very worthy topic of discussion and search engines will find this easier that way. Thanks again for bringing this subject to light.

TominPT

Excellent photos CLLEXUSS. I can't edit the Title as you suggested. I would have not known about this filter had I not seen it discussed in the LS430 forum, which I look at since I also own a '05 LS430. My car has lived its entire life in a low dust and smog environment (western WA state) so I can imagine its fair to say every car at 150,000 miles minimum has their filter pretty much plugged up. I was noticing my climate system going into recirculation mode seemingly at random which was a clue I needed to investigate.