420A 2g GS 420A radiator fans won’t turn on.

[96WhiteEclipse]

Hey guys, my 1996 eclipse gs with the 420A motor coolant fans won’t kick on their own causing it to over heat. When the AC is on both fans will run. However, when the AC is NOT on the cooling fans will not turn on on their own. I replaced the coolant temperature sensor and sending unit which did not solve my problem. It only starts to overheat when sitting at idle/ in traffic for too long. What’s interesting to me however is that when I disconnect the coolant temperature sensor the check engine light illuminates and both fans turn on. What could be the issue here? Could the new part be bad?

 

[luv2rallye]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

 

[96WhiteEclipse]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

Shorted the harness and fans still kick on.

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[96WhiteEclipse]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

I shorted the harness out and the fans came on. What could this mean?

 

[luv2rallye]

Oops. Looks like I said it backwards. Shorting those two wires in the CTS harness should force the fans on - which proves the fans, wiring, fan relays, and PCM are working. It doesn't prove whether the CTS sensor is good/bad. However when the engine gets hot, the CTS sensor's resistance should go near zero (assuming there's enough water in the cooling system to touch it) and so it should turn the fans on. So either your sensor is bad, it's wires are broken, or your cooling system is not full.

 

[96WhiteEclipse]

Oops. Looks like I said it backwards. Shorting those two wires in the CTS harness should force the fans on - which proves the fans, wiring, fan relays, and PCM are working. It doesn't prove whether the CTS sensor is good/bad. However when the engine gets hot, the CTS sensor's resistance should go near zero (assuming there's enough water in the cooling system to touch it) and so it should turn the fans on. So either your sensor is bad, it's wires are broken, or your cooling system is not full.

Well funny enough, I decided to check the connector and clean it and make sure there was a good connection. After that the fans finally began to turn on without the ac being turned on. However, the fan doesn’t kick on until the car starts to overheat. This is the point the fan turned on. Should I be concerned or leave it be?

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[luv2rallye]

Leave it.

 

[96WhiteEclipse]

Leave it.

It wouldn’t cause much damage to my head gasket right?

 

[luv2rallye]

If the temp gauge is only in the middle as shown in post 6 when you say it's overheating, that's normal. If it's pegged that's a different story. If concerned, when cool (to not burn yourself), remove thermostat and run some radiator flush cleaner thru the system (follow can directions running for 15 min) and then after cooling down remove lower main rad hose and reverse flush the system (shoot backwards up thru rad and up hose) with a garden hose pressure. Test if thermostat opens in a pan of boiling water at 195*F or just buy a new one. [Can also get a thermostat that opens at a lower temp if you need (but then you may not get enough heat in winter, although in Oklahoma you probably don't care) although 195* should work anywhere if the rest of the system is working properly.] Put back together - make sure system is burped of trapped air by squeezing lower hose with cap off. If still overheating you may need a new radiator (they don't last forever).

 

[pauleyman]

Get an obd scanner and see what it says coolant temp is. The coolant temp sensor is cheap if you choose to just replace it.

 

[96WhiteEclipse]

If the temp gauge is only in the middle as shown in post 6 when you say it's overheating, that's normal. If it's pegged that's a different story. If concerned, when cool (to not burn yourself), remove thermostat and run some radiator flush cleaner thru the system (follow can directions running for 15 min) and then after cooling down remove lower main rad hose and reverse flush the system (shoot backwards up thru rad and up hose) with a garden hose pressure. Test if thermostat opens in a pan of boiling water at 195*F or just buy a new one. [Can also get a thermostat that opens at a lower temp if you need (but then you may not get enough heat in winter, although in Oklahoma you probably don't care) although 195* should work anywhere if the rest of the system is working properly.] Put back together - make sure system is burped of trapped air by squeezing lower hose with cap off. If still overheating you may need a new radiator (they don't last forever).

The gauge will stay right in the middle for a bit, then creep up before the fan kicks on. That is normal?

 

[99dsmer4g63]

He means the ECT sensor for the ECU not the gauge. There is two sensors on the thermostat housing. Make sure there is no air in the coolant system as this will make the gauge appear erratic at times too.

-Daniel