Ok so I had an over heating problem.

Tested the

Fans - Good
Relays - good
Sensors - kinda old and off by a bit, replaced with new ones
Wirring to fans - good
Wires from ECU - Not sure here...

IF I turn on the AC they turn on fine. So I figured, it must be the sensors... But they were replaced and the fan still doesnt turn on.

Ive notice a couple of things here...

For the Relay, it reads 11.10 instead of of battery voltage. Is this enough for the relay not to switch over? Could it be that it has the voltage but not the current? in which case its the ECU thats bad?

Now if I pull ground for the relay from anywhere else... it works ( positive is still from the relay harness). But, it stays on constantly, regardless of engine temp.

So does the ECU send a ground signal or the positive one?

on the AC fan, when its not on, ground is constant, and the positive is off... flip on the ac and then the voltage goes to 11.52 (engine off). Fans go on, flip it off - fans off. Its weird.

i had a similar problem and it turned out the be a little weight thing inside the motor was sticking so it wouldnt make a connection . clean it and it has been working since

Yeah, but the fans are fine. Even went as far as replacing it with a new one.

Is the fan motor it self good? Also, check and make sure that the fuse in the fuse box for the fan is not blown.

Any signal or sensor that commands the radiator fan relay to activate goes through the ECU. The ECU provides a ground path to the radiator fan relay under the hood. If the radiator fan runs when you turn on the A/C, this confirms that all the relays and motors are okay as the signal to turn on would have to come from the ECU.

The ECU looks at several items to decide about cooling needs. A/C on/off and the two-wire sensor under the thermostat being the main inputs to the ECU to determine if the radiator relay closes or not. The speed sensor is involved as well although I have not investigated how it exactly ties in. I would have to guess at freeway speeds the radiator is commanded to turn off if the temp sensor does not see extreme needs for cooling. Anyone know on the speed sensor issue if it comes into play?

Sorry I can't help more but it looks like you have done the obvious checks. Of course, all this assumes you have no mods to the fan wiring.

Nope, Like It told the guy above. Its not the fan. I even replaced it just to be sure.

Its also not the fuses... thats a basic check.

Dave, If it is indeed a ground signal then it might be the ECU... damn this...

oh and heres how the fans and sensors work

Do both fans turn on when you turn on the AC? Because only the passenger side should.

Only the drivers side should turn on at first, and if it the temps rise high enough then both kick in, and the main fan spins faster.


Exile Racing Technologies
http://www.exileracing.com
Go that way, really fast, if something gets in your way... turn.

look at ebay there is a dude selling a fluidyne(sp) with the fal fans like 200 bucks. all metal baby

Its not a matter of the radiator and fans not being enough. Its already a fluydine with Spal fans and the 180 deg stat.

The fact that the fans arnt working is whats giving problems.

Here is an interesting fact I found out long ago, Both come on with the car off, one with the car on ( AC on). thats with the engine running, not just in the "run" position.

Everything was working fine, untill now, which is why I figured it would be the sensors ( had some issues with MPG and such as well). Now im starting to beleive its the ECU.

But likes other have mentioned... why would that section of the ECU crap out like that?

Edit: another interesting fact. A lot of NT dont have some of the relays and fan set up like its states in the manual... I only have the RAD FAN LO relay and wirring, The sockets are there for the HI but no wires in there...

Bothe AC ones are in there...

Im about to give up... I need a new ecu, or let MS take care of the fans.

Did you isolate and test the wiring between the coolant sensor (and speed sensors I guess) and the ECU? I know the coolant wires are some of the longest ones in the harness...

Hope you get it figured out, I have spare sensors and 2 dsms if you want to come by and swap parts around.

Hey, did you see if the fans were any good?


No NO J/K. I saw that enough in the thread :shrug

Other than that; I got nothing :scratch

Sorry,
MB

bullett...no beer for you.

Think I will take you up on that dawg... drive there with the ac on in this 50 deg weather lol.

Now that you mention in though, I assumed the wires from the sensors to the ecu were good... I should test that.

When I tested the resistnase of the new sensors vs the olds ones, the differences were minor, if any at all.

As far as the speedo wires ( I did re wire things for the MT, but it was working fine for 2 weeks w/o any speedo signal whatsoever). The fact that things just quit is what gets me...