how does the ecu temp sensor work exactly? (elec fan related)

Post by **ANVIL** » Mon Jun 16, 2008 7:48 pm

ok so im just wondering what the voltages should look like. basically im getting majorly frustrated in trying to hook up my electric fan. im trying to use the a SPAL fan controller, which is supposed to work with OEM sensors. basically has a power and a ground for the unit, a power and a ground for the fan and another wire for the temp sensor input. the temp sensor input is supposed to go to the ecu temp sensor signal wire.

the fan has 2 stages for low and high. if i start from a cold start, it will work fine, kicking on exactly when i programmed it to both for high and low. but when it cools down, it never turns off and the voltage stays the same on the temp sensor input. is my sensor bad? if it is should i be getting a new z32 temp sensor or is that the wrong one?

someone please help, i barely get time to work on this thing and this is the only thing holding me back from driving it.
Modified by ANVIL at 11:13 PM 6/16/2008

Post by **Darius** » Tue Jun 17, 2008 3:01 am

So what you are saying is that the controls work properly when the engine is heating up, but if you turn the car off and let it sit for an hour, the fans would still be running?

Post by **ANVIL** » Tue Jun 17, 2008 5:16 am

Darius wrote:So what you are saying is that the controls work properly when the engine is heating up, but if you turn the car off and let it sit for an hour, the fans would still be running?

yes. it has actually done that for longer than an hour, and even when the engine temp has gone way down. took it to a local meet the day i first installed the controller and the fan was going the whole time in high, engine off.

is that normal for the temp sensor to stay at the same voltage? could my ground be bad for the temp sensor? i have a power fc, and thats what i use to monitor my engine temps and it gets the same signal from that same sensor i believe so i dont understand why the voltage would stay the same

Post by **Carl H** » Tue Jun 17, 2008 5:19 am

gotta remember that a temp sensor is nothing more than a thermistor.if the car's coolant stays hot then it will keep registering that thru the sensor.try putting the controller's power on an ignition source rather than a constant.

Post by **ANVIL** » Tue Jun 17, 2008 5:45 am

Carl H wrote:gotta remember that a temp sensor is nothing more than a thermistor.if the car's coolant stays hot then it will keep registering that thru the sensor.try putting the controller's power on an ignition source rather than a constant.

well the controller actually has another wire for ignition, which is hooked up to it, just forgot to mention. i think the seperate power for the unit is for if i turn off the car and its still above the desired temp setting. any ideas on whats going on?

Post by **Carl H** » Tue Jun 17, 2008 6:22 am

perhaps the spal unit is designed for a sensor with different ranges...or is there a programming method to go thru?im not too familar with it.

Post by **ANVIL** » Tue Jun 17, 2008 6:39 am

yeah i think i know how it works. you have to program it.

what you have to do is do a cold start and press the low button when the low fan speed is at whatever temp you want. then you do the same for the high button.

i think it just records what voltage the sensor is at when you press the button, so with the sensor voltage never going down its making it stay on.

i tested it but i dont exactly remember, ill have to do it again but i think it starts around 3 or 4 volts and voltage goes down as the temp goes up. i also tested the difference when the ignition is on and off but i dont remember what i came up with but i think they were different readings. this is just bugging the **** out of me...

Post by **ANVIL** » Tue Jun 17, 2008 7:42 am

can someone test their sensor signal voltage for me?

cold start Voltage with and without ignition onand voltage at full running temp with and without ignition on

and see if the voltage changes after the car is shut off cooling down with and without ignition on.

Post by **ANVIL** » Wed Jun 18, 2008 10:07 am

bump for anyone that can help

Post by **Darius** » Wed Jun 18, 2008 10:22 am

From page EN-318 of the FSM, the coolant temp sensor is supposed to read 1V for 80*C and 3V for 20*C. With the sensor harness disconnected, the voltage at the sensor plug should be 5V.

Post by **ANVIL** » Thu Jun 19, 2008 5:18 am

thanks, ill go test mine after work and see what i come up with.

on a side note, if it is the sensor is there a usdm one i can use for rb25det s1? z32?