Help! Fans not working...no signal from ECU.

[kinday]

Hi...It's quite sad that my introduction to the boards is to get assistance with a problem with my car. but I thank you for the wealth of knowledge I have received from the boards in the past. I have an auto PFL VR4 that absolutely refuses to turn on the fans. It was checked by an auto electrician who checked the entire system and informed me that the ecu is not sending a signal to the fan relay. As a result he set the fan to run direct...once the car is on the fans are running.

Would this be a problem, since the car might have a difficult time achieving operating temperature?
How can I solve the problem with the ecu?

I'll appreciate any help that you can give me to resolve this
And once again thank you CVR4.

[Confused]

The fans are speed controlled by the ECU - it is not a simple on/off signal.

Just behind the fans, is a small unit, that looks a bit like a hedgehog - with a grey connector with 2 thick wires (one blue, one white) and a thin blue wire in the middle. This is the unit that controls the speed to the fans.

The ECU has its own temperature sensor (the dials on the dash have a separate one), which is on the top of the thermostat housing. The ECU one is a 2-pin connector, the dash one is a single-pin connector.


I would guess that either the temperature sensor to the ECU has failed (so the ECU never sees that it is getting warm), which you can verify by reading the ECU with the relevant MUT-II compatible scanner (or, for these simple values, a modified VAG-COM KKL cable and a copy of EvoScan (http://www.evoscan.com)).

Alternatively, if the ECU is seeing the temperature and is outputting the correct signal to the "hedgehog", it could be that the circuitry inside the "hedgehog" has failed, and a replacement "hedgehog" will resolve the issue.

[Davezj]

Hi there and welcome to the club.

the fans on the VR4 do not turn on until a really high temperatures.
not until about 95deg C ish and only very slowly, they do not turn on fully in a cooling the radiator function until the coolant gets to about 110deg C.
but if you turn the air con on the rad fans should come at full speed straight away.

how did you test the fans did not come on at the correct time?

[kinday]

I understand...what the electrician explained to me is

1. He swapped out the coolant temp sensor for another. Even before he replaced the sensor...when he took the sensor out the fans did not turn on.
2. He turned on the a/c and the fans did not turn on.
3. He changed the fan relay. The fans did not turn on
4. He put a direct voltage to the fuse box at the fans relay and the fans engaged immediately.
5. He returned the car to stock system, let the car idle until it started to begin overheating, then checked the output at the ECU and there was no signal to the fan relay.

This is quite frustrating but I'm hoping for the best. He said I'd have to run the fans direct

[BubbaLeggyVR4]

It will be one of the things mentioned above, I work on ecu controlled robots which have 3 phase power and even a silly thing like a trip switch can cause issues.
The brain is normally last to die, other components failing help it along lol
Hope u get it sorted, and Welcome :)

[Davezj]

I understand...what the electrician explained to me is

1. He swapped out the coolant temp sensor for another. Even before he replaced the sensor...when he took the sensor out the fans did not turn on.
2. He turned on the a/c and the fans did not turn on.
3. He changed the fan relay. The fans did not turn on
4. He put a direct voltage to the fuse box at the fans relay and the fans engaged immediately.
5. He returned the car to stock system, let the car idle until it started to begin overheating, then checked the output at the ECU and there was no signal to the fan relay.

This is quite frustrating but I'm hoping for the best. He said I'd have to run the fans direct


sorry if this sounds pedantic but you do not say if the car is running, or off, or ignition is on, off, or acc. so your first 4 statement don't mean much without the relavent extra info.
point 5. how do you define overheating. where you measuring the temperature, did you have the radiator cap in place.

you just have to remeber we don't know anything about your car situation, we only know what you tell us, and at the moment you have not given enough detail.

[kinday]

Got you...how silly of me lol.

The problem began when the car was overheating with the temp gauge very close to red and the coolant overflow bottle bubbling. Radiator cap was never removed until we refilled the radiator and replaced the cap. The we eventually realized the fans were not turning on and we noticed the temperature was at the 3/4 mark on the gauge and rising. At first we assumed it was a bad temp sensor and bought a new one as well as a new fan relay. Replaced the ones on the car but that didn't work. The electrician tested the car starting the car or switching the ignition to the on position as he went along. That's when he said the ECU is faulty

[crazydriver81]

Which one of the temp sensors has been replaced? There are two and only one of them is responsible for the ECU signal...


Bubbling coolant: either overheating or no proper pressure (e.g. not correctly seated rad cap due to aftermarket rad) or exhaust gases in coolant due to defect head gasket

Fans not kicking in: temp sender defect, relay defect, fuse defect, temp resistor ("hedgehog thingy") faulty


According to your description I would change the temp reistor for another one (second hand?) and check again. Next would be to replace the 2-pin temp sender on thermostat housing and if you are at it, replace thermostat as well. Sometimes this gets sticky and does not open far enough to let all the coolant flow to the rad - thus leading to boiling coolant.

[Anderz]

Did you also measure continuity in the cable from ECU fan output pin to the fan controller, could be a broken cable as well, if it is not the temp sensor.
Good thing would be to log Engine temp with evoscan and check if reads ok

[kinday]

Thanks...I'm gonna get some logs with the Evoscan and see whats up. I have a friend who has one