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Discussion Starter #1
Hi for some reason after my obd-1 conversion on my mini me my radiator fans dint want to turn on i checked the relay i checked the fuse they are good what alse could it be.
 

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I no longer haz teh pink eye! Iz got STINK EYE
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3,332 Posts
isnt the one on the back of the block used to turn the fan on and the one on the head used for air/fuel ratio?
 

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a hatch
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1,423 Posts
Ive never seen my fan on and it doesnt go past half on the temp dial
 

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The Great Weldini
91 civic
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8,901 Posts
i had the same problem duck hard wired it so when ever the car is turned on the fan is running.
 

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The Great Weldini
91 civic
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8,901 Posts
look i will say this... i trust duck(vtecduck)we pulled everything we check every line, ground relays everything and we could figure it out. i'll say this duck has being doing car electronics for over 10 years. so we rig it up to turn on when i turn on the car.
 

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Adia's Daddy
2004 Honda Element
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3,364 Posts
isnt the one on the back of the block used to turn the fan on and the one on the head used for air/fuel ratio?
Maybe it's different on different engines but I thought the switch on the block or the thermostat housing was the thermistor/thermoswitch for the radiator fan(s) and the one under the distributor is for the temperature gauge in the cluster?

I assume this because the Honda manual shows how to test the temp gauge circuit by removing the plug from the sensor under the distributor and grounding it to see if the needle shoots all the way to H quickly.

I'm likely wrong though since I'm thinking about it on my '95 and this is an A6 engine being referenced.
 

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1997 Civic Hatch D18Y8 M62 S/C
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2,664 Posts
There is a radiator fan relay in the underhood fuse box that is controlled by a combination of the coolant temp switch on the thermostat housing and the ECU.

There are actually 2 additional coolent sensors under the dizzy; 1 for the gauge cluster and the other goes to the ECU.
 

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Adia's Daddy
2004 Honda Element
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3,364 Posts
There is a radiator fan relay in the underhood fuse box that is controlled by a combination of the coolant temp switch on the thermostat housing and the ECU.

There are actually 2 additional coolent sensors under the dizzy; 1 for the gauge cluster and the other goes to the ECU.
Good to know :td:. I'm going to look up the circuit schematic for them on Monday and memorize how it operates with both sensors in case I get a car in that has a similar issue. I hate just throwing parts at a vehicle to see if it fixes the problem so this info will be of great assistance :bigok:.

From the way I've heard people talk at work, it sounded like it was always usually sensor on the t-stat housing which caused the fans to not come on, barring a bad t-stat itself. The fans stopped working properly on my Civic and replacing the thermistor on the thermostat housing repaired the issue for me.
 

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Adia's Daddy
2004 Honda Element
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3,364 Posts
There is a radiator fan relay in the underhood fuse box that is controlled by a combination of the coolant temp switch on the thermostat housing and the ECU.

There are actually 2 additional coolent sensors under the dizzy; 1 for the gauge cluster and the other goes to the ECU.
Okay I looked today at the wiring schematic for an '89 Civic, '95 Civic and '99 Civic and the circuit works like this:

Battery power is supplied constantly to the power side of the fan relay, and since the relay is a normally open-type, current to the fan motor is cut when the relay is de-energized. When the ignition switch is turned on, power is supplied to the control side of the relay constantly, however the circuit is still open since the ECT sensor opens and closes the ground depending on temperature. When the ECT sensor reaches its designed-temperature, it closes the ground on the control side of the relay, completing the control circuit which energizes the relay. The power side of the realy closes, sending power to the fan motor and turns it on.

The only other item I saw on the schematic was a wire spliced upstream of the ECT sensor which is indicated as going to the ECM. Since the ECT opens or closes ground on the control side of the relay, am I safe in assuming that the ECM applies ground on it's own when it sees a need to in order to bypass the ECT sensor? Or is this spliced wire essentially a "monitor" wire for the ECM to see when the ECT sensor is activating the fans?

I know the single wire small sensor is for the gauge control module. It's just that I was just trying to look for the other sensor under the distributor in the component location index as well as the electrical circuits of the cooling system for all three Civics and couldn't find any at all.

This is bugging me now LOL.
 

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Adia's Daddy
2004 Honda Element
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3,364 Posts
This is the circuit schematic from a '94 Accord so obviously it has more items on it due to the AC system than our Civics do but the radiator fan part of the circuit on the far left like I described is pretty much exact.

 
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