Trans Fluid Temp TFT reading too high ??

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Joined: Tue Apr 02, 2019 10:58 pm
Vehicle: F150, 4.6L, 1998

Trans Fluid Temp TFT reading too high ??

Post by netra » Mon Jun 10, 2019 3:03 am

Working on a trans overheating issue with a 2004 Explorer, 4.6L, 5R55W trans. Using Forscan to read the TFT but it seems to read too high - maybe 15-20 Deg F too high. Trans shop used a Snap-on scanner which read the TFT lower and seemed closer to reality. Also testing with a IR thermometer seemed to agree with the lower Snap-on value. The engine coolant temp seems to be read correctly. Anybody else had a problem like this?

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Re: Trans Fluid Temp TFT reading too high ??

Post by fordnick » Mon Jun 10, 2019 8:36 am

I've found a few that don't seem right. Problem is what can you do in Forscan if you want to make your own custom PID?

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Re: Trans Fluid Temp TFT reading too high ??

Post by FORScan » Tue Jun 11, 2019 12:16 am

FORScan returns PID in the same way as dealership scanner (Ford IDS). We think the problem is that the value returned by module is not "compensated": the sensor function is not linear so a calibration table has to be used in order to convert it properly to degrees. It seems the module in your car doesn't manage such a table so the returned value is a linear function of sensor voltage. We suspect so because we already experienced similar issues with ECT sensor on some models (Focus Mk1, Mondeo Mk3) of the same generation/model year.

It should be possible to fix by implementing such a table. The Snap-On scanner can be used as an ethalon to build it. The problem is that this PID may be used on several or even many models and other modules may manage it properly. So if we replace the converter, these modules will show incorrect values. Anyway, if you are able to build such a table, we will find a way to implement it in FORScan for you.

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