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Old 10-18-2016, 10:41 AM   #1
jackmilas
 
Drives: Yaris Verso 1.3 2000 automatic
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Radiator fan doesn't start when the engine gets hot

Hi,

Here are the symptoms:

- red temperature warning light starts flashing after some time, usually in city traffic
- when the above occurs the radiator fan does not spin
- the fan spins when I engage AC (even when the engine is cold)



I exchanged FAN N.01 relay switch with HORN relay switch to see if the horn works and it does. When I remove the FAN N.01 relay and connect two pins with a wire as marked in the picture below, the fan starts spinning.

relay.png
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Old 10-18-2016, 01:06 PM   #2
jcboy
 
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Based on your observations the trigger of the relay (in the wiring) is faulty, but assuming the AC uses the same relay, then more likely the culprit is the thermoswitch than the thermostat.

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Old 10-18-2016, 02:16 PM   #3
jackmilas
 
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Thermoswitch is normally open?
Is it connected directly to FAN N.01 or FAN N.02 relay?
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Old 10-18-2016, 07:35 PM   #4
CTScott
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The fan No 1 relay coil is controlled by the AC ECU.

It in turn feeds as one of the triggers for the Fan No 2 relay (and gives the AC ECU the ability to turn the fan on when the engine is not hot).

The Fan No 2 relay also has two other triggers in parallel with the AC ECU (so any of the three can turn it on): ECM output CF (cooling fan) and Water temp switch.

The fact that bypassing No 1 makes it turn on just tells you that either the ECM output or the water temp switch is the issue.
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Old 10-19-2016, 01:22 AM   #5
jackmilas
 
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Quote:
Originally Posted by CTScott View Post
The fan No 1 relay coil is controlled by the AC ECU.

It in turn feeds as one of the triggers for the Fan No 2 relay (and gives the AC ECU the ability to turn the fan on when the engine is not hot).

The Fan No 2 relay also has two other triggers in parallel with the AC ECU (so any of the three can turn it on): ECM output CF (cooling fan) and Water temp switch.

The fact that bypassing No 1 makes it turn on just tells you that either the ECM output or the water temp switch is the issue.
Where is the ECM output located?
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Old 10-19-2016, 12:17 PM   #6
jackmilas
 
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Today I managed to get the fan running when I shorted the wires from Water Temp Switch plug. So it seems the switch is not working. I'm replacing it tomorrow.
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Old 10-20-2016, 01:27 AM   #7
CoryM
 
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If you haven't done so, you may want to check your coolant level. Those switches only work when submerged.
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