sunedog

Hi -- I have a 1999 RX300 with 240,000 miles and it threw a CEL. The codes are P0115 (ECT Circuit Malfunction) and P1135 (Air/Fuel Ratio Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). I ordered both a new engine coolant temperature sensor and air/fuel ratio sensor.

I have a pretty good handle on the air/fuel sensor replacement from some excellent write-ups here, but I can't seem to find much on the engine coolant temperature sensor replacement.

First off, I can't even locate the darn thing. Can someone describe where it is on my vehicle? I did see a sensor right near the center of the front of the radiator, but it is connected to a thin pipe with a sightglass. Is that it?

Once I find it, is there anything else I should know before replacing it?

TIA

artbuc

Highly doubt you need a new ECT sensor. Usually you get a P0125 companion code along with the A/F sensor code. Never heard of P0115 as a companion code but I bet it is. It is very easy to check the ECT sensor if you have a VOM tester. Chances of both A/F and ECT sensor failing at the same time are slim and none.

sunedog

I thought the same thing, but bought both and may return the one I don't need. But the ride has 240,000 miles on it so I may replace both anyway. The ECT sensor was only $26.

BUT I still need to find where it is located before I can replace it.

sunedog

Think I have found what I am looking for. Ironically didn't come across this using this forum's search function. Found it through a Google search:

Thanks to Lexmex for the pictures.

https://www.clublexus.com/forums/2889437-post3.html

salimshah

When it comes to sensors, please use OEM.

Salim

sunedog

I've been reading all the great info on the A/F sensor on this forum. Ordered:

Denso 234-9009 $91.50 delivered

Delphi TS10198 Engine Coolant Temperature Sensor $25.99 delivered

salimshah

The second one is a Delphi. Hope it work out well for you.

Salim

CubFan22

Thanks Salim for the info and DIY on the ECT sensor.
I am getting the P0125 also. Keeps coming back after I clear it after 10 miles of driving the car.

carguy07

Any other codes?

sunedog

Following up to share my experience.

I pulled the air / fuel ratio sensor from below the firewall. Bench tested it and confirmed it was dead. Replaced it with the one I got from Amazon. Cleared codes by disconnecting the battery for a few minutes. (Tried to pull the fuse referenced in the other thread, but that did not reset my CEL.)

Thanks to everyone who contributed to the thread on replacing the rear air / fuel sensor. I was able to do it with your excellent guidance.

I never installed the coolant temperature sensor. No CEL came on after I replaced the air / fuel sensor.

One more thing: I replaced the battery just before replacing the air / fuel sensor. It was dying and I had it load tested and it was confirmed bad. I don't know if that could have contributed to my multiple codes or not.

artbuc

Can you return the ECT sensor?

sunedog

Yes. I bought it from Amazon and used their painless return procedure. Cost me about $6 in return shipping and handling, but that is it.

forHeisris

Ordered the Delphi ECT sensor from Amazon. It is made in Mexico. Is this the right part or should it be made in Japan?

Zarkove

Hello ! New guy here !! I'm having a serious doubt with my rx300 cooling system; it's a 01 model and it only has 1 temp switch closed to the thermostat, there is non on the radiator or even losen plug : what happens that it takes quite long for the radiator fans to kick in and when they do it doesn't take them more than 15 to 20 secs max for them to come off and then it will take at least 5 minutes foe them to come on again , while the engine is running on idle. is this normal ? Shouldn't they run a bit longer ? All help appreciated 😩

davidt238

I know I am a little late in the game, but on my 2003 RX 300 the ECT Sensor is located on top of the engine, on the left side, near the back, out in the open and very accessible. I just removed the connector and put a deep-well socket on and easily removed it. I hope you found it, and had an easy time of it as well!