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#1 Old 08-13-2007, 09:09 PM
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Default Help with testing coolant temp sensor

I have reason to believe it is malfunctioning.

I have a 2001 LC accent with the 1.5 SOHC and no A/C. If I'm looking at this right, the coolant temp sensor is on the thermostat housing, and based on it's readings, determines whether the radiator fans turns on or not.

Well, the fan hasn't been turning on so I've been running hot. I tested the fan and it works.

I've searched HMA service and couldn't find a testing procedure for the sensor. I looked and there are three contacts on the sensor that plug into blue, orange, and black wires on the harness.

How do I test to see if it's working correctly? Am I measuring resistance or voltage, and on which pins? Anybody have any wisdom on this? Like right now? (the hood is up and I need to know asap... =)


Thanks!

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#2 Old 08-14-2007, 02:35 PM
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Did you test if any volts are going to the fan with ur DMM
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#3 Old 08-14-2007, 02:52 PM
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To test it, you unplug the connector and measure the resistance across its teminals with an ohmmeter. When the coolant is cold it should read 7,000 to 14,000 ohms while when at operating temp it should read 700-1,000 ohm. If it doesn't change in that approximate way, then change it!
Remember you might need to use a t pin

Another test of the wiring is to have the engine warmed up and running and then remove the sensor's plug which if the wiring is o.k. will cause the cooling fan to start up.
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#4 Old 08-14-2007, 03:05 PM
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Thanks so much for the help, alex!

I gave the fan 12V and it spins no problem. I tested the fuse/breaker and that is fine. I have not tested to see if the fan is getting voltage through the harness though.

So the best way to test that is to unplug the sensor off the harness as you say, and that should instantly send a current to the fan, right? so if I unplug the sensor and it DOESN'T start up, then it's either the wiring or the control module/relay.... where the heck is that thingy?

Ok, so to test the sensor itself, there are three contacts. which ones do I measure the resistance across? The two outside pins? Or the middle one and the right one? I have no idea.

thank you again so much!

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#5 Old 08-14-2007, 03:44 PM
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Ok here are te specs off my 00 accent they should be same for you right 18.1 ohms center 80.3 ohms left 1.641 ohms if you unplug that sensor the fan should kick on in like 4 secs if it does not let me know
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#6 Old 08-14-2007, 11:25 PM
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Quote:
Originally Posted by alexw3
Ok here are te specs off my 00 accent they should be same for you right 18.1 ohms center 80.3 ohms left 1.641 ohms if you unplug that sensor the fan should kick on in like 4 secs if it does not let me know
ok, I measured the resistance between the left and right terminals. (I don't know if that's the right way to measure) I forgot to check before starting the car (sorry, idiot here) but as the car was warmed up, I had a reading of around 355 ohms. When the coolant was cool and warming up, it read around 950ohms and steadily dropped as the car warmed up. I don't know if I'm measuring the resistance across the proper terminals or what, because the readings seem to be way off of your numbers!

The temp gauge in the car seems to read properly.

When I unplugged it, the fan DID turn on, so that's good. But once I turn the car off, the fan keeps going! Is this normal?

argh... I hate this. thanks for your help, alex. what do you recommend I do next? Did I even test the sensor properly?

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#7 Old 08-15-2007, 03:58 PM
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Ok did you test the neg lead to a good ground and pos to each wire. The volts should slowly drop as the car heats up. The fan stayed on when you turned off the car? did you plug back in the CTS?? Let me test my CTS again I was in a hurry yesterday so I might not have got good readings. With the CTS pluged in let the car idle to normal temp does the fan come on at all.
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#8 Old 08-15-2007, 04:18 PM
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Ok my bad I did not let the car warm up all the way Blk 131.3 ohms blue Na orange na because resistance is to high switch to volts and blue 11.38v orange 5.13v ok that should be about right.
Ok 4 my first post dont pay any attenton to the specs they are off another car try to use mine (00 accent 1.5l) they should be the same as ur readings

Last edited by alexw3; 08-15-2007 at 04:20 PM.
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#9 Old 08-15-2007, 04:19 PM
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Alex, I was getting no voltage through any of the three terminals, so I measured resistance between the left and right terminals on the sensor. That was the only way I could get any kind of reading.

I tried the fan thing again and it stays on if I turn the car off and the sensor is unplugged. The fan does not seem to turn on when I plug the sensor in and the engine is over hot. (I can tell when it gets over hot because it smells... that's what alerted me to the problem in the first place)

man, I seriously owe you a pack of beer for this!

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#10 Old 08-15-2007, 04:20 PM
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I'll let the car warm up again and check the voltages again to make sure.

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