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Discussion Starter · #1 ·
I have had the CEL come on a few times but it never stays on for more than a couple minutes at a time. Every time I try to get somewhere that I can check the code the light goes off. So tonight I decide I'll just see if anything shows up when I check it at home. So there wasn't any CEL on, but when I check it shows code 15. When I look that up it says coolant temp sensor high fault. The engine always shows that it is running just less than the middle of the temp gauge. So I don't think it is really running hot.

I also can't seem to find the ECT sensor, from what I read it should be a 2 wire sensor. Can someone guid me to where it should be. I have a 1994 Sidekick JLX 4 door 1.6L 16V.

Any advice on how to test the sensor? Could this be causing a decrease in fuel mileage, like 3 mpg less?
 

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The temp gauge and what the computer is looking at are two different sensors. If it is intermittent and comes and goes, I would suspect grounding or wiring issues. The coolant temp really doesn't change THAT fast!

A 16 valve motor, there are two or three sensors near the thermostat. One for the computer, one for the gauge and one for the AC (if equipped.)
 

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Discussion Starter · #3 ·
So I unhooked the negative battery cable to clear the codes. As soon as I keyed on it immediately showed code 15 again. I assume that means it read high coolant temp all the time. So thinking the sensor or ground is not working all the time now.
 

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Measure the resistance of the sensor or the voltage at the sensor, Code 15 is most likely to be a bad sensor or a short to ground in the wiring.
 

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The temperature gauge on your dash is pretty meaningless, unless suddenly the needle is sitting in a place where it never was before. Mine has sat at 1/4 for 18 years, even though the engine is completely warmed up.
Normally a code 15 (high temp indicated by the coolant temp sensor) means that the wires to it have shorted - check the red/yellow wire to the sensor. The FSM test for this is to clear the code (and you can do this by removing the dome light fuse for a minute, rather than disconnecting the battery). Then disconnect the coolant temp sensor and start the engine. If you look at the engine by the thermostat housing, you will see two connections that look exactly alike - one of them is a greenish color, with a red/yellow and gray/yellow wire running to it. That's the coolant temp sensor (ECT). If you disconnect the connector to it after you have cleared the codes, then start the engine and see if you now get a code 14, or if you still get the code 15. If you now get a code 14, then you have a short in the red/yellow wire. If you still get the code 15, then the coolant temp sensor is faulty.
 

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Discussion Starter · #6 ·
I unplugged the sensor and reset the ECU. After I powered it back up and keyed on it immediately flashed code 14. However, after I plugged it back in it flashed code 12. I drove it for a day and the next morning the CEL was on when I started it. The code 15 was back. I assume that it takes some time for the ECU to flag the ECT high. I've picked up a new sensor and plan on replacing it this weekend. I will check the resisitance before I pull it out to replace just in case it is fine.
 

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If you got the code 14 with the sensor unplugged, then it most probably is a wiring problem, rather than the sensor itself. Red/yellow wire shorted to ground. However, it's a good idea to replace the ECT anyway - its been there a long time. But if the problem is wiring, you will still have your code 15, even with your new sensor.
 
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