Question about 2002 Honda Odyssey

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99 honda odyssey coolant fans turn too late

My odyssey coolant fans only turn on at a very high temperature(close to hot) i changed the coolant fan switch sensor and the sending sensor and still fans turn on too late why is this ?

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You might need a new ECT - engine coolant temperature sensor. If it's not reading the correct coolant temperature it's not going to tell the fan to turn on when it should.

Is the check engine light illuminated? I'd bet the ECT needs replacement.

Posted on Dec 17, 2008

  • Car Fixer Dec 17, 2008

    Sorry I didn't read your post all the way through ;-) I'd still be interested to know if a trouble code has been triggered.

    If the sensor has been replaced then I would focus on the wiring & connections next. The wires may be rubbing or shorting out and causing a wacky reading. Trace the wires leading to and from the appropriate sensors. Although this specifically isn't your code, it does give you some things to consider - Good luck!



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Why does my fan always run intermittently? During traffic jams my fan will run about 25 times intermittently, and I check my temperature it is still normal?

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I don't know what a March is, not sold in the US under that name. But I would suspect on that newer a model, the ecu turns the fan on when the Coolant Temperature Sensor on the engine registers a hot coolant temperature which requires the fan for extra cooling.

On older model Nissans (like my '87 Sentra) there is a switch about half way down on the radiator (look for a 2 wire connector to it). When the coolant temperature reaches 192 degrees F., the thermistor contacts close, and the fan relay turns the fan on. When the temperature drops below 181 degrees F., the contacts open and the fan stops running.

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Cooling fan wont come on car running at a high tem

You could verify fan motor is good by using jumper wires from battery to the fan motor. If the motor is good, you will probably need a wiring diagram and at least a test light to start checking the fan circuit. There will be a cooling fan relay that when signaled, will send power direct to the fan. The signaler to relay to turn the fan on may be the engine computer when the coolant temperature sensor tells it engine is getting too hot- or it may be signaled on by a fan temperature switch mounted in the radiator. When coolant reaches a set temperature the switch closes contact, and the relay is energized to pass power on to the fan. One could pull the relay and with key on, use test light to probe the terminals where relay plugs in. The power feed for the fan should light up the test light on one of the terminals, verifying power is still available to turn the fan on. Next one could check if the signaler to turn the relay on is working.
See? So you do need a wiring diagram to see how the circuit is wired. But the first step is to verify fan motor is good. Good luck, Nigel.

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Fan sensor is not working.

You need to change the relay and the temp sensor switch. If you have done that the reason it's not coming on is probably because the coolant is not getting hot enough to cause it to come on. Let me explain. The coolant fan when the A/C is off is activated by the coolant fan switch. The switch closes when coolant temperature is over 238F completing a path to ground through the coolant fan relay windings. The relay contacts then close and voltage is applied to the coolant fan. When the coolant temperature drops to 214F, the switch opens and the coolant fan stops. In A/C equipped vehicles, the A/C control head completes a path to ground for the coolant fan relay whenever the A/C is on no matter what the temperature. Voltage is then applied to the coolant fan. Essentially, the coolant fan switch is by-passed when the A/C is on, which is why the fan works whenever you turn the A/C on. Now, if the fan does not kick in when the coolant temperature is over 238F but works when the A/C is on, the problem has to be the coolant fan switch or the connectors or wiring to the CFS.

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Radiator fan switch or coolant temp sensor however it is called is not activating the radiator fan when temperature is high. . .iS THERE a way to by pass this switch or sensor so it can activate the...


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I have a 1999 honda civic lx its was running hot so i changed the radiator the thermestat water pump timing belt but now it will not run hot but the temp gage goes real close to H before it goes back...

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1 Answer

Engine runs hot

Most often that is caused by a bad thermostat.

How to test the thermostat in most vehicles;

Make sure the heater is off, start the engine and let it run for 6 to 8 minutes, ( this will allow the
engine to reach, " normal operating temperature "), from the inside of the vehicle turn the heater
temperature on high and turn the fan speed on high.
1. Listen very closely for a click sound from the engine, ( most thermostats make a click when
they open )
2. Watch your temperature guage, it should begin to lower as the coolant starts to circulate.
3. Usually within a few minutes the radiator fan will kick.

What the thermostat does;

It seperates your coolant into two parts. The first part is in your engine, the second part is in your
radiator and the coolant reservior. When the coolant in the engine reaches the temperature rating
on the thermostat the thermostat opens to allow the two parts of coolant to change places. Now
the cooled coolant in the radiator and reservior flows into the engine while the heated coolant flows
from the engine into the radiator and reservior to be air cooled by the radiator fan.

I hope this helps you.

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