Strange fan behaviour
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Teching In
Joined: Aug 2015
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From: Dnepropetrovsk, Ukraine
Strange fan behaviour Hello everyone!
I have another one issue linked or not with this https://ls1tech.com/forums/lt1-lt4-m...mp-95-lt1.html one.
Need your advice and suggestions!
About month ago when my water pump started to leak, exactly that day I tried to reach home and in a half of my way I visited a shop where I parked my car and switched off the engine. When I returned to my car I noticed that tha fan is still tries to cool down the engine and some coolant leak form the pump detected. I thought was that some air passed to the water pump and there is no any coolant around the ECT sensor and it gives to the PCM a wrong data about the temperature. So I drove to home and all the way fan was working. Then at home I switched off the engine but the fan was working too. I don't know how the fans work on these cars from the factory, but mine often work some time after the engine is switched off - it is about 1-2 minutes in winter and up to 5-10 mintutes in summer. But this time it is already passed about 20 minutes and the fan is still working. So I went to my fuse box and tried to pull out all three relays and also a 10A fuse. But the fan still worked. Then I decided to disconnect the battery and it helped. I gave two hours to the engine to cool down and connected the battery again - fan didn't start again. That was the last day I used the car.
Two weeks ago I tried to start the car but the battery was discharged to 6 volts and it was surprise for me.
Today I brought well charged battery to my car, connected it. Turned a key to the 'on' position but didn't start the engine and then swithed off again and pull out a key. And in 20 seconds the fan is started again and yes - on a cold engine that didn't run about a month. Also tried to pull out all relays and fuses - didn't help. Also a fuse for PCM.
I know that my car is '95 and has a three relay configuration when two fans work at low speed and at high when it needed. But my car has a setup when the second fan is operated by the manual switch and only runs when I switch it. But what can be with my first fan??? How to check it?
Within a few days I will receive my own built cable to read the PCM about what temperature is from the ECT sensor and what fan relays it commands to run or not. But I think something is wrong with the fan.
Thank you very much!
I have another one issue linked or not with this https://ls1tech.com/forums/lt1-lt4-m...mp-95-lt1.html one.
Need your advice and suggestions!
About month ago when my water pump started to leak, exactly that day I tried to reach home and in a half of my way I visited a shop where I parked my car and switched off the engine. When I returned to my car I noticed that tha fan is still tries to cool down the engine and some coolant leak form the pump detected. I thought was that some air passed to the water pump and there is no any coolant around the ECT sensor and it gives to the PCM a wrong data about the temperature. So I drove to home and all the way fan was working. Then at home I switched off the engine but the fan was working too. I don't know how the fans work on these cars from the factory, but mine often work some time after the engine is switched off - it is about 1-2 minutes in winter and up to 5-10 mintutes in summer. But this time it is already passed about 20 minutes and the fan is still working. So I went to my fuse box and tried to pull out all three relays and also a 10A fuse. But the fan still worked. Then I decided to disconnect the battery and it helped. I gave two hours to the engine to cool down and connected the battery again - fan didn't start again. That was the last day I used the car.
Two weeks ago I tried to start the car but the battery was discharged to 6 volts and it was surprise for me.
Today I brought well charged battery to my car, connected it. Turned a key to the 'on' position but didn't start the engine and then swithed off again and pull out a key. And in 20 seconds the fan is started again and yes - on a cold engine that didn't run about a month. Also tried to pull out all relays and fuses - didn't help. Also a fuse for PCM.
I know that my car is '95 and has a three relay configuration when two fans work at low speed and at high when it needed. But my car has a setup when the second fan is operated by the manual switch and only runs when I switch it. But what can be with my first fan??? How to check it?
Within a few days I will receive my own built cable to read the PCM about what temperature is from the ECT sensor and what fan relays it commands to run or not. But I think something is wrong with the fan.
Thank you very much!
TECH Regular
Joined: Nov 2011
Posts: 471
Likes: 14
From: Tucker, GA
I think I remember reading somewhere that a bad coolant temp sensor can also trigger the primary fan to run
Last edited by atlantadan; Jun 18, 2017 at 04:55 PM.
Thread Starter
Teching In
Joined: Aug 2015
Posts: 5
Likes: 0
From: Dnepropetrovsk, Ukraine
According to http://shbox.com/1/4th_gen_tech2.html website...
I think that you are completely right about bad ECT sensor. I have read somewhere that if you are disconneting this sensor it will also causes the fans to start. Thus the PCM tries to protect the engine from overheating.
There are two versions of the dual fan configuration:
1993-1994 - Primary and Secondary fans that operate at only one speed. When initially commanded on, only the primary fan (driver side) comes on. It operates alone at full speed. If the temp threshold is met for addtional cooling, the secondary fan (passenger side) also is commanded on. At this point, both fans are running at full speed.
These fans use a two relay architecture that can be seen in the fuse/relay panel that is under the hood.
In late 1994 and into 1995, there was a change to low and high speed fans. When initially commanded on, both fans will come on at a low speed. When the high speed temp threshold is met, they both bump up to high speed. A three relay architecture is used for this fan version (seen in the fuse/relay panel). By adding a third relay, low speed can be achieved by running the power to the fans in series. This way, each fan does not get full voltage and runs at a slower speed. High speed happens when the relays switch to provide full voltage to both fans. Low speed is less noisy and should result in greater fan longevity. High speed is not always needed.
1993-1994 - Primary and Secondary fans that operate at only one speed. When initially commanded on, only the primary fan (driver side) comes on. It operates alone at full speed. If the temp threshold is met for addtional cooling, the secondary fan (passenger side) also is commanded on. At this point, both fans are running at full speed.
These fans use a two relay architecture that can be seen in the fuse/relay panel that is under the hood.
In late 1994 and into 1995, there was a change to low and high speed fans. When initially commanded on, both fans will come on at a low speed. When the high speed temp threshold is met, they both bump up to high speed. A three relay architecture is used for this fan version (seen in the fuse/relay panel). By adding a third relay, low speed can be achieved by running the power to the fans in series. This way, each fan does not get full voltage and runs at a slower speed. High speed happens when the relays switch to provide full voltage to both fans. Low speed is less noisy and should result in greater fan longevity. High speed is not always needed.
Thread Starter
Teching In
Joined: Aug 2015
Posts: 5
Likes: 0
From: Dnepropetrovsk, Ukraine
Hello again!
Long story short. It took me only first five minutes under the car to get frustrated!
So, tracing the wires clarified me that my cooling fans system was completely modified compared to the stock one. Someone decided that he doesn't trust the GM way to cool the engine. So for now cooling fans system is completely separated from the ECT sensor in the water pump and the PCM. It works like... ...just look at the my diagram...
http://www.mediafire.com/file/gq2tyv...ns_Diagram.jpg
After the discovery I took that relay for test. And if I connect 12 volts to the relay it works well - starts clicking. I assumed that if relay is healthy than the issue is in that custom ECT, that is installed in the hose that goes from thermostat to the radiator. I don't know why it is failed. But there is an easy way to go, just replace it while replacing a water pump, when all of the coolant will be drained.
But I will try to find a way to return to the stock fan system setup, when three rerkay system is used and both fans operate low and high speed togetger.Thus I need to test all the wiring between PCM, fuse box and fans.Diagrams and images of stock wiring of the fans system will be the best.
Thank you very much!!!
Long story short. It took me only first five minutes under the car to get frustrated!
So, tracing the wires clarified me that my cooling fans system was completely modified compared to the stock one. Someone decided that he doesn't trust the GM way to cool the engine. So for now cooling fans system is completely separated from the ECT sensor in the water pump and the PCM. It works like... ...just look at the my diagram...
http://www.mediafire.com/file/gq2tyv...ns_Diagram.jpg
After the discovery I took that relay for test. And if I connect 12 volts to the relay it works well - starts clicking. I assumed that if relay is healthy than the issue is in that custom ECT, that is installed in the hose that goes from thermostat to the radiator. I don't know why it is failed. But there is an easy way to go, just replace it while replacing a water pump, when all of the coolant will be drained.
But I will try to find a way to return to the stock fan system setup, when three rerkay system is used and both fans operate low and high speed togetger.Thus I need to test all the wiring between PCM, fuse box and fans.Diagrams and images of stock wiring of the fans system will be the best.
Thank you very much!!!
Part 1
So the fans motors can have the same ground that the relays use (battery or frame)
Wire gauge should be at least as thick as the stock wires (black and blue color)
Use the relay to turn the high current fan wire (blue) on and off. The switch should not have current going thru it, 20-30 amp switches are usually large so using a relay will allow for a smaller switch.
Part 2
Using the ECT sensor to activate the ground on the fans will bow the ECT sensor up is it is not current rated. I would use the ECT to ground out the activation of the relay, instead of using it to ground the fan.
Here is a really rough idea of what I'm saying.
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
That's the way folks used to override the ecu temp setting before the programming became as mainstream. I just did the same thing to my Honda because it wasn't calling for fan until 238 degrees.
