01LEXPL

iTrader: (10)

I realized this last night coming home that my fans are going full tilt, even though the car was still 'cold'...

Which brings me to my next series of problem solving. The car doesn't overheat or remain cold - meaning the thermostat is okay.

I changed the 'main engine' relay [for some reason it is labelled as such on the relay cover], this controls the fans, upon removing it they turn off. Bad relay, right?

I tested the relay it read ~70 ohms. But still, unsure of the threshold for functioning relays I went out and bought one to isolate the problem. Didn't fix it.

Did some more lurking online, I ran through the wiring, and looms. All is well, it should be functional. One thread in particular led me to a guy finding a frayed wire in the AC drier/evaporator canister being linked to the cooling system. Fair enough - all was well there.

I ran the motor, and pulled the plug for the coolant temp. sensor and immediately triggered the CEL/TRAC icons, and shuddered - while the fans were still running.

I cleared the CEL by pulling the positive terminal off, since it was a self-inflicted code.

I'm stumped, I don't want to go about ordering all sorts of things for this car since it will be sold soon... but I don't want to overwork my fans for no reason and solve the issue.

Thanks

ES300NZ

In alot of cars, the ECU triggers the fan relay.
- the ecu uses the ECU water temp sensor (THW?) to perform the calculations which tell is whether or not to turn them on, and whether it is half speed one fat, full speed one fan, half speed both fans, or full speed both fans.
- The trigger is an earth connection often, so the relay gets triggered by the ecu connecting an earth connection.

- I would think about replacing that sensor,
- and checking the wires in the relay socket, by having a good look at the back of them, see if they are being shorted out somehow.
- the fan relay is relay F not the 'main' one.

LeX2K

If you don't have it, get a hold of the factory service manual it outlines the steps to take to test the fan system. The fans are a "fail safe" design meaning if anything goes bad the fans always run, so the first thing you need to do is test ECT switch #1 on the bottom of the rad. If you find no continuity when the engine is cold the switch is bad.

GSGenesis

Thought I replied to this.... Are you another with the same issue?

01LEXPL

iTrader: (10)

^ I just made this thread today, I've looked at the few resources I could find online. And there isn't much.

I've maximized my [limited] resources for the weekend anyways. I will be going to the shop on monday to check that sensor out to confirm.

I'm not looking forward to having to source such a sensor... If the relay was a 3 day wait at my local Lexus dealer....

ES300NZ

If it's helpful. Most engine water temperature sensors are 400ohm resistors. they operate by dropping resistance the moment (and I do MOMENT), they are exposed to heat. The react very very quickly.

I was monitoring one once, it started at 400ohms, we started the engine, it dropped to 396 super quick (2secs), the the resistance fell from there as the engine heated up until the fan kicked in and arrested the fall

75-85 degrees (C) is about 200 - 180 ohms.

LeX2K

http://imgur.com/a/aEcAF

ES300NZ

^what a legend.

01LEXPL

iTrader: (10)

Thanks for the diagrams, Lexus2000.

In my case it was relays for Fan no.1 & Fan no.3.

So changing the main engine relay was pointless and 40$ down the drain - oh well.

I simply went to the yard where i have two 99 GS300/400's and grabbed the relays out of those - works like a charm.

Thanks for the help gentlemen

ES300NZ

awesome