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Old 04-08-2012, 12:04 PM   #31
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Originally Posted by DevilDogDoc View Post
^^^ Hmmm.
Yup, one wire totes a fixed ref voltage from ECU to sensor...Usually 5 volts on most cars....The other wire totes the signal back....The ECU compares the return voltage to ref voltage and based on the difference, decides if engine is in proper operating temp range....if ECU detects no return voltage or out of range voltage, it pops a code and usually commands engine go into limp mode...You 02 sensors work basicly the same way.On most cars that use only one sensor, the ECU also sends a signal to dash temp gauge.

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Old 04-08-2012, 12:45 PM   #32
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I'm bored at work today, so I just measured voltage to my temp sensor with my Fluke 73 DVM at connector on loom side...it's 5.15 VDC with key on, engine off.

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Old 04-08-2012, 01:59 PM   #33
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Yep some sensors like my aftermarket ATF temp sensor have a single connection for the wire that goes to the gauge so their brass body is the other contact that must get its ground connection through its mounting threads. That's a type of sensor you can't use teflon tape on.

The sensors I've worked with on the TJ all seem to have all their electrical connections made via their electrial connector so they don't depend on the sensor to get its ground via whatever it is threaded into.

And yep, the sensors will typically have 5v on them which comes from the PCM.
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Old 04-08-2012, 02:46 PM   #34
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Originally Posted by Jerry Bransford View Post
Yep some sensors like my aftermarket ATF temp sensor have a single connection for the wire that goes to the gauge so their brass body is the other contact that must get its ground connection through its mounting threads. That's a type of sensor you can't use teflon tape on.

The sensors I've worked with on the TJ all seem to have all their electrical connections made via their electrial connector so they don't depend on the sensor to get its ground via whatever it is threaded into.

And yep, the sensors will typically have 5v on them which comes from the PCM.
Where does your aftermarket ATF temp gauge gets it's ref voltage and at what voltage is it?...I'm asking cause I'm thinking of certain dash mods.
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Old 04-08-2012, 09:25 PM   #35
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Where does your aftermarket ATF temp gauge gets it's ref voltage and at what voltage is it?...I'm asking cause I'm thinking of certain dash mods.
The sender acts as as variable resistor in series with the gauge's ground side with 12 volts being on the other side of the gauge.
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Old 04-08-2012, 10:28 PM   #36
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The sender acts as as variable resistor in series with the gauge's ground side with 12 volts being on the other side of the gauge.
Thanks, that makes sense, and also makes an idea do-able maybe
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Old 04-09-2012, 01:45 AM   #37
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Oh, BTW...if you decide to measure voltage to your temp sensor, it will pop a code and CEL will light until cleared/reset by code reader device...Code P0118.

It just means sensor voltage was open or out of spec due to your testing...Good part is it also tests CEL and tells you it's got your back in case of real event....And no, it won't put you in limp mode. Promise

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