98 Civic EX 4-door automatic.
I want check the coolant temperature at the radiator as if the car is driving down the road, with lots of air flowing through the radiator. I figured the best way to do that is to force the radiator fan to stay on. How do I do that? The fan kicks on at about 210 degrees and shuts off at about 195, so there must be a switch somewhere. Can somebody tell me where? (P.S. It is NOT the coolant temp sensor near the thermostat -- when I short out that connector, all I get is a check-engine light, but no fan.)

 

It IS the 2-wire switch on the thermostat housing. What are the wire colors in the connector?

 

Wires are red and green. It is a sensor, not an on-off switch, and it is a couple inches below the thermostat housing, not on the housing. My shop manual shows a SWITCH right in the thermostat housing for some engines, but mine does not have that. The manual says the SENSOR has resistance of several thousand ohms (very cold) down to almost zero ohms (coolant at about 210). I have checked the sensor from 60 degrees up to 190 degrees, and the resistance is correct per the chart in the manual.

So I figured maybe the computer turns the fan on based on the sensor, and if I shorted it out it would simulate hot coolant and turn on the fan. WRONG. So there must be an actual switch somewhere else.

 

Post clear pictures. The radiator fan switch has a green wire and a black wire.

 

This^ connector is for the ECT sensor or IAT sensor. Post pictures of the wires or also give the stripe colors on the two wires.

 

Sorry, can't get a picture of the actual car tonight, but I certainly understand the confusion. The image you posted is exactly what is in my shop manual, and is what you see if you go to the Majestic Honda online parts lookup. The manual describes testing of this switch to assure it turns on and off -- lots different from the sensor.

See page 11-76 of the same manual, which has a little graph of resistance at various temps -- also calls the sensor a thermistor, and it can set codes P0116 through P0118. See also page 11-47 for a description. My car has the thermistor, but absolutely does NOT have the SWITCH screwed into the thermostat housing. Like I say, there has to BE a switch, but it must be somewhere else. On the radiator, maybe???

 

You need to post the stripe colors on the red and green wires. That connector is probably for the ECT sensor, which is for the 2-wire sensor located under the distributor of the D16Y8 engine. Is that the engine installed in your car?

 

Yes, I have the D16Y8 engine, and yes, that is the ECT sensor. But getting back to my original question, there is no ECT SWITCH where we expect to find one. I wonder where it is?

 

You obviously don't want to jump that connector because you risk blowing the ECU. So the sensor you've been referring to is located below and slightly forward (front of car) of the distributor?

You either have a hybrid engine or somebody put the wrong thermostat housing on your engine.

Again, pictures will help. Start by locating the 2P connector with one green wire and one black wire, which are for the fan switch.

Consider that your engine may not have an ECT switch.

 

Does your block say D16Y8?

 

I finally found it. It is at the back of the engine toward the firewall, in the housing where the radiator hose returns from the bottom of the radiator. Thanks for your help!