2001 F250 5.4/4r100. I bought this truck in pretty rough shape last summer for use around our farm and locally. It has an approximately 4 year old Jasper reman 4r100 in it.

I seem to have a bad TFT sensor. In Forscan I get TFT Fault and a reading of 5.0 volts pretty much at all times with the blinking overdrive light. Once in a while, after everything is good and warm, the sensor will seem to kick back in, and give reasonable temperature readings and kick the flashing OD light off.

As I understand it, this sensor is integral to the solinoid pack, and not easily replaceable. I'm wondering if this sensor provides information to the PCM that is important for the operation of the transmission? This is mostly a farm/driveway plow truck for us and I'm not inclined to put a lot of $$ into it. If the sensor isn't providing info that the PCM uses aside from turning on warning lights I'm inclined to put a resistor in the wiring in order to get the warning light to turn off, and install a stand alone trans temp gauge.

Alternatively, I'm thinking about installing a temp sender in the test port of the trans, cutting the wires from the trans plug that go to the internal tft sensor and
connecting them to the sender in the test port.

The only complicating factor in both of these plans is that the wiring plug on this transmission does not correspond to the pinouts I have been able to find online.

Anyone have any thoughts for me? Much appreciated.
Matt

 

Solenoid pack is simply to replace, and a good rebuilt unit is under 200 bucks

I'd check the plug into the solenoid pack first, it's in a spot where water kid salt can get into it very easily. Check for corrosion and or chafed wires

 

The plug looks good to me, but that's a good thought. I'll give it a good cleaning and see if that improves things. I'm also a little hesitant to replace the solinoid pack since it looks like my plug is no longer wired in the stock configuration. I guess I could get a new plug and chase down which wires are which with from a pcm pinout

 

Yes, it does. Shifting pressures are changed with temperature.

I seem to remember a test that the PCM runs that requires the reading from the sensor to change. If it doesn't change it sets a code and flashes the OD OFF light.

That won't work. The output of the sensor and the aftermarket gauge sender are very, very different.

 

I appreciate your insights. Sounds like my ideas are unlikely to be worth the effort.

With regard to the shifting pressures, do you know if I'm running risk of damage driving with this bad sensor or does the trans go into a kind of fail safe mode?

Thanks again,
Matt

 

It will go into a failsafe mode to protect itself.