Engine Coolant Temp (ECT) sensor questions

[FormulaIntegra]

1995 Civic EX, D16Z6. So, looking at my shop manual, and under my hood, there are 3 sensors:

1. Engine Coolant Temperature Switch, which is located at the thermostat housing, and tells the radiator fan relay to turn on, via the ECU.

2. Engine Coolant Sending Unit, which is the single wire post under the distributor cap that goes directly to the temp gauge on the dash.

3. Engine Coolant Temperature Sensor, also under the distributer cap, and looks suspiciously just like the ECT switch....which I can't seem to find in my Honda factory manual, and is labeled in one of the pictures in the back of my Haynes manual, but no explanation for what it does, where it goes, etc.

It doesn't seem like my radiator fan is coming on when it should, and I'm trying to track down whether it's a bad sensor, and if so, which one, or if the relay is bad. Anyone know what the Temp sensor does, as opposed to the sending unit or temp switch, on this engine? The factory manual doesn't have a pin out for the ecu, so I don't know if it's looking for info from the switch and the sensor, or what. Any info would be helpful. TIA.

[speedracer9k]

unplug the sensor off the t-stat housing and take a paper clip and jump to 2 terminals on the connector. the fans should come on. if they dont the fans dont work. if they come on, then you have another problem. try that and let me know.

[FormulaIntegra]

Originally Posted by speedracer9k

unplug the sensor off the t-stat housing and take a paper clip and jump to 2 terminals on the connector. the fans should come on. if they dont the fans dont work. if they come on, then you have another problem. try that and let me know.

So, first of all, I wired straight from the battery to the radiator fan, and that worked, so I know the fan motor itself is not the issue. Next, I tried your suggestion to pull the ECT switch connector at the thermostat housing, and jumpered it with a paperclip. I could hear the fan relay clicking in the engine fuse box, but the fan wouldn't come on. What does that mean?

Also, the other sensor, the one underneath the distributor, what does it do, and how does it factor in to the system?

[robbys89]

sounds like your fan relay is gone. replace and see what happens. the sensor under the distributor is the temp sensor that tells you the temp of the engine on your cluster thats all

[TsunamiR]

You should check if there are sensors in the 5 volt control!

[civic_driver]

1. Engine Coolant Temperature Switch, which is located at the thermostat housing, and tells the radiator fan relay to turn on, via the ECU.

The ECU doesn't control the ECT switch on the thermostat housing. The temperature controls it. Once it reaches a certain temperature (can't remember off the top of my head, around 80 degrees celsius) the switch activates which in turns activates the radiator fan. The ECU controls the radiator relay though, maybe that's what you were thinking of.

I think you have a loose wire between the relay and the radiator fan.

2. Engine Coolant Sending Unit, which is the single wire post under the distributor cap that goes directly to the temp gauge on the dash.

Right.

3. Engine Coolant Temperature Sensor, also under the distributer cap, and looks suspiciously just like the ECT switch....which I can't seem to find in my Honda factory manual, and is labeled in one of the pictures in the back of my Haynes manual, but no explanation for what it does, where it goes, etc.

This is not a switch. It's a sensor that reports the coolant temperature to the ECU. The ECU uses this to find out if the engine is cold in which case it adds more fuel so the engine can warm up faster. The ECT sensors is also used to adjust spark, EGR function, open/closed loop feedback, idle speed and so on.

[FormulaIntegra]

Awesome info, thanks guys.

I love when I get to do a whole ton of troubleshooting, tracing wires through the harness, looking for a broken wire or one shorting to ground, taking apart the underhood fuse box because I wasn't getting continuity on one of the connections to the fan relay. After doing all that, it ends up simply being a blown fuse in the underhood box. I swear I thought I checked them all before I started, but as soon as I replaced the fuse and jumpered the t-stat temp sensor connection, the relay clicked and the fan came on. I love it when I get to learn a bunch about a system, and the fix ends up being something inexpensive and easy.

I usually believe in trying the easiest things first, but you don't learn as much that way. Sometimes the hard way is more rewarding.

[civic_driver]

Isn't that the truth... Great stuff

[hondatango]

ok i have followed all this in to a t and replaced all sensor except under the distributor and still gauge works but fan still not kick on should i replace that sensor too? i also replaced relay just incase and jumped the pins to test fan and the fan runs but when car gts hot it not kick on help please lol

[RonJ@HT]

Bleed the cooling system.

[roze1981]

I've had the same problem and my car's light was on for 2 years. I have been to Honda dealer and other mechanics but couldn't fix it.
Last month I went to this guy in downtown toronto and he could fix it.
anybody has the same problem go to this guy he can do miracles.

PM me for contact information.

cheers,
Roze

[95Prelude2go]

My 95 prelude with h22a1 in it and i unplug my ect and car runs better
So I took a ect sensor off h22 a4 same sensor and car doesn't change but when I unplug runs better should I check wires to Ecu

[CBL9]

Sorry to being this back from the dead, but I searched and found this.

I have a 1995 Civic EX 145k on it bought it over the summer with 138k. Up until winter the temp gauge on the cluster never reached the "point right below half" on the cluster. It would stay at half of that approximately 1/2 between cold and where it should have been.

Now that winter is here the gauge moves 1-2mm making its way from below cold to the cold level. The car does not heat up well IMO. Today I just sort of jumped the gun, bought a gasket and thermostat and replaced it, and bled the cooling system.

I let it idle for 1/2 hour and the fan never came on. The coolant gauge on the cluster moved no more today than it did in the past, just that 1-2mm. I checked the fan fuse under the hood, that was intact. I switched the AC on and the AC fan came right on.

I do not know how long the fan has not been working for. I want to know if I have two separate issues here or one bigger issue causing these two problems of

1.) Radiator fan not working
2.) Cluster needle moving a very tiny amount

Thanks Guys!!!

[grumblemarc]

Does the fan actually work? Not coming on is not the same thing.

[CBL9]

Originally Posted by grumblemarc

Does the fan actually work? Not coming on is not the same thing.

I am not sure. How can I test that?

[motegicivic]

I have a feeling it is not hot enough for the fan to come on, pull the plug off the thermostat housing and use a paperclip to jump it (bend like a "U" put one end in each plug opening) turn the car to position 2 and see if the fan runs.

So you are saying the car seems to run too cool?

[MonkeyBoy668]

Just want to throw this out there, but there are some lousy third party parts floating around these days. It's not unheard of to buy a new in box tstat and not have it work.

The cheapest way to check one is the stovetop method... get a medium size pot, fill it most of the way with water, place thermostat in water, place thermometer in water, turn on heat to high, and if the thermostat responds at the correct temps then it's good. Otherwise it's bad. The values for initial open & full open are in the Helm service manual.

[CBL9]

Originally Posted by motegicivic

I have a feeling it is not hot enough for the fan to come on, pull the plug off the thermostat housing and use a paperclip to jump it (bend like a "U" put one end in each plug opening) turn the car to position 2 and see if the fan runs.

So you are saying the car seems to run too cool?

Fan came on immediately when I jumped the opening. I used some spare copper wire as paper clip wouldn't stay in the connector. So then I went to put the connector on and find that on the sensor itself it appears that the little "nubb" which the female end snaps on too is broken off....

So if the female connector that I just jumped is slipping off the sensor enough to not make contact would that describe my symptoms?

So I wired the sensor as tightly as I could together to hold it in place. I went for a test drive and the gauge came up almost all the way to normal operating temperature.

I then let the car idle for another twenty minutes. But the fan still did not come on. The heat in the car felt great btw.

So what should I do next? Would that thermostat sensor with a loose connection cause my symptoms? Anyone want to unplug theirs, drive around and see what happens???? And let me know

Thanks!!

-Tony

[motegicivic]

Replace the fan switch on the thermostat, sounds like it might be broke or the tab is not making a connection with the harness.

[ekhatchc5]

ct sends signal for amount of fuel for the right temp

[blackbirdoor]

hi guys, first time posting here. Lately, around the cold winter weather, i notice that my '96 accord v6 would be hard to start after sitting outside overnight, found out that it was the starter that was starting to fail. new starter put in couple days later, been functioning good for the past week and a half. this morning when i started my car, it sounded like it was trying to turn over, but couldn't turn over, only after a couple of tries did the car finally starts. I had to assist with the gas pedal a couple times to get it going, but it finally went. Then CEL comes on,code is p0118 (ECT high voltage, or loose circuitry issue), autozone diagnosed it as a possible engine coolant temperature sensor that might have gone bad. Im thinking, does that have anything to do with my car having a hard start in the morning ( or any time of day)? I searched around for the engine coolant temp sensor, autozone gave a picture of what it looks like, but i can't narrow it down to which area under the hood should i be looking at, is it on top of where the thermostat housing sit? or is it below the distributor area that i should be looking at? any pictures of the thing is appreciated Coolant is full (no leaks), replaced the thermostat around last june or so, temp gauge is slightly below middle mark, indicating that thermostat is opening/closing properly.

[94EG8]

This isn't the accord section, but yes a bad ECT can cause hard starting or a no start condition.

[blackbirdoor]

ah, i do apologize, google search took me to this page i was reading into it so much i forget that its a different section from what i wanted, also any idea where its located under the hood? thank you again for the reply!

[spoolnpsi]

Where is the coolant switch located on a 91 civic dx....It's not on the therm housing.

[jbpnoman]

Originally Posted by spoolnpsi

Where is the coolant switch located on a 91 civic dx....It's not on the therm housing.

Maybe you should ask in the EF section. This is the EG/EJ section.