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  #1  
Old 06-05-2002, 10:00 PM
gcookaustin
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Adding resistor to tranny temp sensor

I think I could easily add a resistor to the tranny temp sensor, if I knew where it was. Is the sensor a bunch of electronic stuff or just a simple thermal-coil thing with a wire going in and one coming out? I was thinking I could measure the resistance when cold and again when the TC locks up to get a good idea of what resistance to use (using the temperature-resistance equation we learned in Physics but I forgot!) That way the AT light could come on at say 220F instead of 325F.
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  #2  
Old 06-05-2002, 10:14 PM
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The fact remains that the TCU turns the light on - not the sensor. Anything altering the sensor signal will effectively alter the TCU programming.
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  #3  
Old 06-05-2002, 11:29 PM
gcookaustin
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Oh. Well but if the sensor sends a signal that corresponds with 325F, regardless of what the temperature really is, wouldn't that cause the TCU to turn the light on?
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Old 06-05-2002, 11:35 PM
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Sure, but the TCU also communicates with the ECU and who knows what is in the programming. Normally they would only share vehicle speed info, etc. but I wouldn't put it past Subaru to have made a few other 'connections'.

If you really have your heart set on making that light useful how about plumbing in a 'tee' fitting and wiring an aftermarket temp sensor to the light? Simpler and prolly safer than possibly messing up your TCU...just a thought.
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Old 06-06-2002, 02:46 AM
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temperature Warning Indication

This is something which had crossed my mind and I think is a subject worth pursuing as accessory gauge is not something I realy wish to have to stick some where but I would like to know if the temp. is exceeding 200. Others may be of like mind.

Beav you have a practical answer as usual but it would be nice not to have to hack into the original wiring. First we must establish the actual function of the sensing device. I.E. Is it a true transducer which provides the facility to measure a variation in temperature or is it simply an on off device calibrated for a fixed temperature.

Beav your comments would indicate the former in which case the TCU makes use of the variation in temperature for other control functions which would indicate a very high degree of sophistication. Is the sensor described anywhere or its electrical function discernible from a wiring diagram ?

Once again you are being asked a curly one but hope you will remain resilient . If you say go find out some place else I will understand and even agree with you. Again special regards, Trevor.
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Last edited by Trevor; 06-06-2002 at 02:52 AM.
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  #6  
Old 06-06-2002, 05:10 AM
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The tranny thermocouple or RTD is not linear in it's temperature verses voltage drop. The leads from the sensor come into the connector for the TCU. This would be the place where I would splice in the wires to hook up a resistor in series(? I have to check). IT would be an experiment only because the several different resistors would have to be tried.

The other part of this, that is important is that the fluid in the tranny pan as read by the sensor in the pan, the one we are talking about above.

The other part that is important is that not all the tranny pump flow goes to the cooler. The pump takes fluid out of the sump and after the pump the flow path splits. Some of that fluid is sent it off to some parts of the tranny and a portion of the fluid that goes thru the lock-up valve and then the Torque Converter and then the goes out to the cooler, where most of us have a thermometer.

From what I see on my temperature gauge when the tranny is locked-up and the TC is bypassed, the pan temperature is read on the gauge and it is lower than when the TC is not locked up.

I also think it is possible that the lock-up valve is used as temperature control valve in this arrangement but I haven't checked it out yet.

John
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  #7  
Old 06-06-2002, 10:59 AM
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The temp sensor is shown on the diagram in my locker.
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  #8  
Old 06-06-2002, 03:21 PM
gcookaustin
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AKA dropping resistor?
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  #9  
Old 06-06-2002, 03:30 PM
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Lightbulb

Hmm.. Mebbe that's the same temp sensor that tells the TCU not to shift into 4th until it reaches a decent temp?
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  #10  
Old 06-06-2002, 07:23 PM
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Quote:
Originally posted by gcookaustin
AKA dropping resistor?
No, the dropping resistor is the one behind the battery. The temp sensor appears on the upper right of the schematic.
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  #11  
Old 06-06-2002, 07:23 PM
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Quote:
Originally posted by Boone
Hmm.. Mebbe that's the same temp sensor that tells the TCU not to shift into 4th until it reaches a decent temp?
That would be the one and the same.
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  #12  
Old 06-06-2002, 07:33 PM
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Quote:
Originally posted by Beav


That would be the one and the same.
My tranny shifts into 4th fairly quick...it takes a long time to lock up the TC though.
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Old 06-06-2002, 08:04 PM
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Quote:
Originally posted by Earthworm
My tranny shifts into 4th fairly quick...it takes a long time to lock up the TC though.
So does mine, I'd like to change that aspect and think of a way to enable TCC lock-up in third gear without resorting to a manual switch.
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  #14  
Old 06-06-2002, 09:45 PM
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Temp. Sensor

Sorry Beav and thanks John.

I should have recalled that I had printed the diagram from your locker Beav some time ago and now referring to it see that the sensor is drawn as a variable resistor which confirms what John says i.e. it is a transducer.

If it is in fact a true thermocouple in a classic thermocouple circuit it would be unwise to play with it. Furthermore as it would appear to have more than one function altering its calibration would be a no no. Therefore this would appear to be an end to this possible mod. but it has been interesting conjecture.

I have been thinking of fitting a temp. gauge and from what John says the sensor should go in the sump and wonder if this could be arranged when the next service is done. I presume space could be found and a fitting brazed in.

Regards all, Trevor.
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  #15  
Old 06-06-2002, 09:47 PM
gcookaustin
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Quote:
Originally posted by Beav


No, the dropping resistor is the one behind the battery. The temp sensor appears on the upper right of the schematic.
Oh, okay I see. So is there a visible wire somewhere that I could get to? The sensor looks like it's embedded well into the transmission. I guess all you would have to do is either trial and error, or if you had two different temperatures to measure the resistance over the sensor then you could plug the resistance and temperatures into the equation p1=p0*(1+a*(t1-t0)) to get 'a'. Solving for 'a' would lead to the amount of resistance you need to add to the wire leading to/away from the temperature sensor.
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