'91 Tracer, coolant sensors, no fan

Fan doesn't seem to work while driving, but will come on, both high and low speed, when the computer is put in self-test mode. Is the sensor bad or whatelse? There are 3 sensors right together: one for
the dash gauge, one for the engine coolant, and the other i don't know. Any ideas. Something for the trans maybe. Thx.
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I think the correct front to back order for the 3 coolant temperature sensors is
1. Computer 2. Dash Gauge 3. Fan
The one for the dash gauge is the smaller one wire one. The other two are identical looking, however the wiring harness plugs are made so that you can't plug them into the wrong one. You need to check the one for your fan.
However, the first thing I'd do is check fan and computer ones for dirty contacts.
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Why is there a sensor for the computer and fan? Would you please explain how each do their job? Am baffled why there is 2. Thx.

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Can someone tell me how to test the sensors, if possible? Haynes book i have only tells how to test sensor for dash gauge. Thx.

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