I replaced my coolent temp sensor about a week ago, at that time I also replaced the wiring and pigtail that someone had cut prior to my owning the car. Since that time the cooling fan runs constantly. Today I replaced the coolent temp sensor again think that I may have gotten a bad sensor, the engine warmed to about 130 degrees and the fan came on and now will not cut off. When I wired the unit I used the green and white wire for the power wire( I believe that was the wire originally) and ran the other side to a ground. What am I doing wrong? Is there something I can check? Any suggestions are appreciated.

Jody

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1992 25Th Anniversary Camaro
305 TBI
5 Speed

 

Jody,

What is the part number of the coolant sensor you are using?

I only ask because the TBI cars use a hard contact switch to control the fan relay, and TPI cars use an analog resistance sensor to signal the ECM, and the ECM controls the fan relay, not the sensor directly.

If you install an analog resistance sensor in place of a hard contact switch, once the sensor warms to a point and the resistance drops accordingly, the relay will have enough current flow to ground to energize. Since it requires far less current to hold the relay closed than to pull it in, the temperature can drop significantly (and the sensor resistance increase) and the relay will remain closed. If you were given an incorrect part, you may have this situation. I would suspect that this might be the case, since the replacement sensor apparently has two connections instead of just one, as most hard contact switches have.

Incidently, at 130°F, the resistance of an analog sensor is about 800 ohms, which might be just low enough to pull in the relay. At 140°F, it lowers to 650 ohms, etc.

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Later,
Vader
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"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0

[This message has been edited by Vader (edited March 02, 2001).]

 

It sounds like you may have just been replacing the wrong sensor. The fan is controlled by an on/off switch that grounds the circuit to the block after 225 degrees, turning the fan on. It is in the passenger side cylinder head between plugs 6 and 8. The coolant temp sensor is by the thermostat housing and tells the computer the coolant temp via a change in resistance. The ECM and the fan switch are not related.

89 Transam GTA, a few bolt ons

 

TA,

Here's the primary cooling fan circuit on YOUR GTA:



The ECM and fan are not related?

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Later,
Vader
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"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0

 

I realize that mine is related because it's TPI. We were talking about a TBI which is different. The computer does not control the fan on TBI and carburated engines.

89 Transam GTA, a few bolt ons