Transmission fluid temperature voltage

[crunchie_frog]

I got around to piddling with the free FORSCAN software yesterday. I was amazed at all the different sensors it could display. I guess pretty much the same thing that the ECM reads but you can see it all, trend the information and store the files so you can look at it later.

My question is I was trying to monitor my transmission fluid temperature and the information the ECM gets is voltage, there was no conversion to temperature in the software or from the ECM. I was wanting to know if anyone knows the voltage to temperature conversion for the transmission sensor. thanks

 

[2000StreetRod]

thermistor

I know the 5R55E has an internal thermistor to sense the ATF temperature but I wasn't aware the 4R70W had one. The wiring diagram for the 5.0L PCM shows pin 37 as Transmission Fluid Temperature (ECT) Sensor Input which is connected to the Transmission Fluid Temperature (TFT) Sensor in the 4R70W. A note on the diagram states: "The PCM monitors the voltage drop across a temperature sensitive thermistor. The PCM uses this information to determine transmission fluid temperature for adjustment of shift schedules and torque converter clutch engagement schedules. Also used to adjust EPC pressure for temperature." Since the PCM pin has ECT in parentheses the sensor may be identical to the one used for engine coolant.

 

[SoNic67]

As a side-note, the app "Torque" (Android platform) shows directly the temperature in degrees.

 

[crunchie_frog]

I know the 5R55E has an internal thermistor to sense the ATF temperature but I wasn't aware the 4R70W had one. The wiring diagram for the 5.0L PCM shows pin 37 as Transmission Fluid Temperature (ECT) Sensor Input which is connected to the Transmission Fluid Temperature (TFT) Sensor in the 4R70W. A note on the diagram states: "The PCM monitors the voltage drop across a temperature sensitive thermistor. The PCM uses this information to determine transmission fluid temperature for adjustment of shift schedules and torque converter clutch engagement schedules. Also used to adjust EPC pressure for temperature." Since the PCM pin has ECT in parentheses the sensor may be identical to the one used for engine coolant.
View attachment 79355

Thanks, my steady state voltage was around 0.90 volts which would give a trans fluid temp of about 170 deg F, which, I think, sounds about right for a typical hot South Carolina day with no load. I wonder where the sensor is located? I rebuilt a 4R70w a few years ago and I do not remember seeing one.

 

[SoNic67]

TOT sensor below:

 

[rb142]

170F would be low for those conditions. It's probably a lot closer to 200. All programs have TOT (trans oil temp). Don't assume that the transfer curve is the same as for ECT though. TOT would have a higher temp range.

TOT is one of the standard parameters in the live data, so it is easier to read that message and have it already scaled.

 

[SoNic67]

Mine is 180-185F on highway (I have the factory aux cooler). In stop&go traffic, at 90's outside, it gets higher.
200F would be too high IMO.

 

[crunchie_frog]

I checked the voltage this morning, it was 2.66 volts and using the chart provided by StreetRod (and fitting the data to a curve) gave me ~82 degrees. The intake air temp read 82 and the coolant temp read 80 so, at least at this temp, the voltage to temp relation for the ECT sensor appears to be correct. There is no TOT in the PID selections for FORSCAN so I cannot read the temp directly from FORSCAN only volts.

This vehicle has an air auxiliary trans fluid cooler so the fluid temp could be cooler than the coolant temp so I guess 170 degrees on the highway is not out of the question. I am changing my oil today so I will check the pan temp with a IR gun and see if it is close to the temp I get with the chart and that to me would confirm the chart is correct. I know it is correct at ambient temps.

 

[crunchie_frog]

Ok, I checked the temp of the pan after driving about 15 minutes and it was 137 F. The voltage was 1.37 which is about 139 deg F. So, my conclusion is the chart supplied by StreetRod is correct for converting the volts signal read on Forscan for the TFT (Transmission Fluid Temp) and that my highway temp fo 170 F the other day was correct. Thanks StreetRod for the chart and thanks Sonic for the info on the location of the sensor.