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Discussion Starter #1
My Radiator fan turns on during start even of the engine is cold or even when you put the key to ON. (not start). Temperature sensor is good.

This problem started after we rebuilt the engine. Now I don't know where to look.
 

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Discussion Starter #2
By the way, the fan still run even if I display connect the temp sensor, looks like it was connected directly to the switch. Pls help.
 

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Sounds like your ECT sensor or the wiring between the sensor and the engine computer is open circuit. Using a diagnostic scan tool to read the sensor output would confirm. If the temperature value is something like -30 ~ -40'C the circuit is open somewhere.
 

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Check the radiator fan relay
It may be stuck on.

Also, it can tell you which way to test next
Either the control side of the circuit or the load side
 

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Check the radiator fan relay
It may be stuck on.
Personally, I wouldn't bother because if you stop and think about it the relay can't really be stuck on.

avisitor said:
Also, it can tell you which way to test next
Either the control side of the circuit or the load side
Well, it's nice to know at least one person reads my posts about testing relay circuits.

But in this case we already know from the OP's opening statement ("My Radiator fan turns on") that the relay load circuit is working properly.
If the problem was on the load circuit the fan would either never switch off (stuck relay) or never run at all (open load circuit).

So there seems to be a problem on the relay control circuit. Specifically a short to ground on the relay control wire which would cause the fan to run as soon as the ignition is switched on. That seems to fit the OP's symptoms, but the other possibility is (and more likely, in my experience) that the fan is just being commanded on incorrectly by the engine PCM.

So, just for a giggle, here is your mission if you choose to accept it....devise a test that will allow us to determine whether the fault is being caused by a short to ground on the relay control wire, or an incorrect command from the engine PCM. I've drawn a sample fan control circuit diagram so you can see how the fan works if that helps.

 

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Just test the control wire
Check it for short to ground with the wire disconnected from the PCM
If no short then test the wire with the PCM connected

I don't know if the power to the load side is hot at all times or hot only when the key is turned to the on position
This is why I suggested the relay may be stuck
It is always easier to troubleshoot a circuit when one knows the circuit
But, not all circuits and relay circuits are controlled or powered up the same way.

And what do you expect from an auto parts sales person
Oh, switch my job to being a driver to deliver parts to commercial customers
Unfortunately, very slow lately
 

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Discussion Starter #8
Thank you very much Aviator and Auto spark. Both your contribution are very helpful to me. Either way, I will check both your suggestions. Again MARAMING SALAMAT. That means thank you very much in Filipino
 

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Discussion Starter #9
I now having a hard start when engine is hot, which I think the ECT is not working which probably was cause but the fan always running. ?
 

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I now having a hard start when engine is hot, which I think the ECT is not working which probably was cause but the fan always running. ?
That would be my guess. Although, it might not be the sensor itself that's causing the problem.

The hard starting is probably being caused by the PCM injecting too much fuel because it thinks the engine is really cold (-30 ~ -40'C).
 

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Just test the control wire
Check it for short to ground with the wire disconnected from the PCM
If no short then test the wire with the PCM connected
You could certainly do it that way but before going to all that trouble what I would try is unplug the relay and connect a voltmeter across the control terminals. then monitor the voltage as you turn the ignition on and see how long it takes for the meter to show 12V.

If the control wire is shorted to ground it will show 12V as soon as the ignition is on. If the PCM is commanding the fan on there will be a short delay before the voltage shows. Generally, it takes the PCM a second or two to recognize the incorrect input from the sensor and switch the fan control wire to ground.

Of course, if you have a scan tool you could just use that to monitor the PCM fan output. I doubt a generic OBD tool would have the fan control data pids though so you'd need a tool that's bit more Hyundai specific.

avisitor said:
It is always easier to troubleshoot a circuit when one knows the circuit
Yes, it certainly does help one with one's diagnosis when one knows how the circuit is wired.

avisitor said:
Oh, switch my job to being a driver to deliver parts to commercial customers Unfortunately, very slow lately
Congrats on the new job. There was a parts store near where I live looking for a delivery driver a while back. I was very tempted to apply for the job. A driving job beats what I'm doing now.
 

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Discussion Starter #12
I am overwhelm by all your help. I can't thank you so much. I'll probably just bring my car to hyundai shop to have it check.
 
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