no idea, I have driven the car with #4 broken for years without any noticeable issue. you may want to shift your focus/money to bigger issues

 

Oh, I've shifted $$ to this old LS400 alright - and while expensive to fix - still enjoy driving it. I knocked the vacuum hoses off of #4 sensor while replacing the starter - and thought some one may know what it's for. I thought my Toyota Tech downloads may have the answer - but I can't find it.
Looking to replace the brake pads later today.

 

I find that if you have the factory service manuals and a lot of good tools and the know-how, the LS400 is one of the cheapest cars to fix - it seems almost every problem is a $40 part - strut bar bushing, IACV, transmission mount, coolant temp sensor, ECU caps, and many other examples!

One month's payment on a new luxury sedan would about buy a lifetime supply of LS400 parts for the DIY mechanic!

 

absolutely right lets spend your saving money on something else

 

I only needed to pay just 1/100th of 1 month's payment on a beautiful donor car which is the same year model.

I am a DIY guy and I am expecting to keep the car till I die. But nothing was broken for the past 1 year and I was not able to enjoy my DIYs. The donor car runs still great and it can be registered if I want. But I don't need too many cars since the silver car next to Celsior is also mine.

 

Wish my parts cost $40 - You don't own a 1990(?) - but agreed that the LS400 is not difficult to work on. I do the work - just replaced rear pads yesterday.
A few items I have replaced include: hydraulic shocks (@ $1800 a piece? - nope) - replaced with conventional suspension system ($800 ), Console electronics reconditioned part - ($125), starter replacement (gaskets, rebuilt starter motor, fuel injectors reconditioned, wires plugs, etc - ($500) I broke the cold start hose under the air box - $85 too), Power steering pump leaked onto the alternator - both replaced while daughter was visiting in California - had to pay shop labor and parts - $1200!
Yes still less than a few new car payments - but I have yet to find many parts (I've needed) for just $40. (Did I mention a leaking coolant reservoir - $75 at the bone yard? - or the steering column gear replacement (way under $40 - $9.99 to be exact.)?
But my LS400 is running great, silent and comfortable - and a pleasure t drive.
As far as the sensor on the top radiator hose outlet - (#4)? I researched it a while ago but cannot recall what I found out - have the time now.
Yes - I'm selfish, and have used the forum for years - without posting - but have had some time to add and respond lately (before getting busy with work again). Many of the posts (including yours) at Clublexus have been helpful over the years, thanks.

 

never run your lexus with out all sensors operating there is one for cold start injector-one for egr operation -one for temp sender and the one you can not see which is located under the right coil and is your ecu . If your gas mileage is under 16 mpg you need to do this one now.The book says 2.5 hours to do this repair but can be done in less then 20 minutes.remove the coil assy- take off the wire cap-which is alittle hard to do,car must be cold first.use a 11/16 deep socket which you will see is the only one that will fit over the sensor.the part should be less then 40 dollars.make sure to glue the washer on to the sensor so it will not fall off when installing -take your time and tighten real snag like spark plugs.this repair at the dealers is over 225 dollars.

 

Hahaha seriously when I read he's just deleting sensors I was like wtfff. They obviously do something even if its not obvious.

 

I too believe the sensor IS there for a reason and mine is apparently operating (after reattaching with gasket sealer). But will replace and give an update when I recall what its for. Although I get great gas milage I will also replace the #2 - under the coil assembly.

The car is technologically amazing for 25 years old - it has redundant systems and all have a purpose.

 

This is what shows on Alldata for the cooling system sensor/switch locations.

 

Thanks - but there is another sensor on the first generation (mine's a 1990) - check out the first picture in this thread - its labeled as #4.

 

Lexus Parts > 90925-05068
Lexus Part:
VALVE, BIMETAL VACUUM SWITCHING
Part NO.: 90925-05068
Genuine Lexus Parts backed by Manufacturers WarrantyShipped quickly from Authorized Lexus DealershipLowest Price with Award Winning Customer Service
Your Price:$55.99
Lexus's Retail Price:$74.39
You Save:$18.40
Qty. Add OEM Lexus Valve to Cart
To check if it fits my car & get more parts info, click here.
Compatibility Info:
Part No. 90925-05068 fits the vehicle applications listed below:
ModelProduction DateEngineTransmissionTrimBodyDoor
ES300 1991.07-1993.08 6cyl 3.0L MTM
ES300 1991.07-1993.08 6cyl 3.0L ATM
ES250 1989.06-1991.07 4cyl 2.5L HT
LS400 1989.05-1990.08 8cyl 4.0L SED

 

Wow, love your LS yamae! (I am looking to get those exact same wheels for my LS)

 

I know this is old... is there any way you could send me the picture? Seems it's not there anymore. Thanks

 

That member has not logged in since 4-2018, unfortunately getting pics would be slim.

May try here:
https://archive.org/web/