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Discussion Starter #1 (Edited)
A couple of days ago I had my gauge go crazy on me and the dash started to light up and said to check transmission temperature and tow haul flashed. I left it alone, after I drove around a bit, the temperature according to Torque was in the 70's (obviously wrong) but the trans was functioning OK. Then the next day, all was well, no lights, not trouble, transmission gauge seem to register.



Yesterday when the Gage again went screwy, the truck started jumping in and out of gear and shifting incredibly hard. There was 10 second Period Where the truck completely disengaged even in drive. After the temperature went up on the gauge to about 70°, the truck started shifting normally again.


So after some research I figured it was the TFT sensor. I went ahead and replaced that sensor today. However now that I have everything back together I decided to do a quick check from the gauges to see if the sensor was registering properly now before I bolted the pan back up. My OBD scanner indicates that the sensor is still reading 8123.6° it does not seem to be changing. The dash gauge at key on shows the trans gauge being 'cold'. When you start the truck, the gauge goes completely dead, tow haul comes on, and truck complains about temperature of the trans. Torque app indicates temperature is steady at 8,000+ degrees.


EDIT TO ADD: Truck was not started without fluid. Only after I added fluid did I start the truck. Before I bolted the pan and filled, I tested the sensor with Engine Off/Key On to verify function, it did not read properly, so I bolted up and filled.




I visually inspected the connector in the transmission and the wires on it briefly and saw no issues. I filled up the transmission in hopes that it would work. Anyway it doesnt, so I suspect I'm going to be draining my brand new fluid. Before calling it a day, I checked wires under the dash, I traced the harness from the transmission to a box on the drivers side, All of that visually looks fine. No damage to the conduit. I wiggles all the wires I could reach around the transmission and where it terminates on teh firewall while I was hooked up to Torque, and the reading never changes.


Im at a complete loss and pretty bummed. This is my work truck, and I'm not sure how I'm going to get this fixed.

I attempted to test my old sensor with my multimeter. At about 68 degrees, the sensor reads about 30 kOhms. That number changes if I warm up the sensor. I now suspect that the old sensor was perfectly fine.


I need help desperately for troubleshooting this. I have never had any issues with this gauge for 166,000 miles. One day it was fine, the next it wasn't, and upon replacing the sensor with a new one, its even worse. At least before it would read SOMETHING that was in the 50-70F range.










Help please..... :(
 

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When you start the truck, the gauge goes completely dead, tow haul comes on, and truck complains about temperature of the trans. Torque app indicates temperature is steady at 8,000+ degrees.
Did I read this right? Did you start the engine before filling the transmission? If you did, there is a good chance that you've caused serious damage to the pump. It really doesn't like running without oil.

I visually inspected the connector in the transmission and the wires on it briefly and saw no issues.
That doesn't eliminate the wiring as being the problem. It just means the problem is not extremely obvious. You need to electrically check the wiring from the PCM to the TFT.
 

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Discussion Starter #4 (Edited)
Did I read this right? Did you start the engine before filling the transmission? If you did, there is a good chance that you've caused serious damage to the pump. It really doesn't like running without oil.


That doesn't eliminate the wiring as being the problem. It just means the problem is not extremely obvious. You need to electrically check the wiring from the PCM to the TFT.

Hey Mark, to be clear, the truck WAS NOT STARTED WITHOUT FLUID. Only key on to validate sensor function.


Now I have to really test before I go opening up the trans again.


I have a pretty nice multimeter and am ready to find the problem. Only code is P0713. Literally the only code on the truck, and its thrown immediately.

I have the battery tray out and access to the PCM Connector for the transmission as well as access to the connector at the transmission. Surely there is a way to test the TFT pin for shorts or damage to at least isolate the location. My Ford Service manual says that "TFT SIGNAL" is Pin 18. I don't know what to probe or what to test to isolate the issue. What do I do?
 

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Discussion Starter #5
Bump

Maybe I got a dud TFT sensor. I have wiggled and unplugged wires from the transmission to the PCM. There is zero possible way on this planet a wire harness 'goes bad'. They don't 'go bad'. They are damaged or they aren't. The wire harness looks as good as it did when I brought it home from the dealer. I have no idea what else to do here except throw in another 15 dollar sensor and hope for the best. Otherwise, I'll have to tow it to a shop because she won't shift without a TFT reading.

Help is appreciated.
 

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Surely there is a way to test the TFT pin for shorts or damage to at least isolate the location. My Ford Service manual says that "TFT SIGNAL" is Pin 18. I don't know what to probe or what to test to isolate the issue. What do I do?
Remove the connector from the PCM. BACKPROBE pin 18. DO NOT put a probe in the end that mates to the PCM. That can spread the pin and cause a new problem. At the same time backprobe the signal return pin on the PCM connector. I don't have a diagram to tell you which pin this is. Someone else will have it. If that shows an open circuit or a zero ohm connection you have a problem. While keeping the probe on the back of pin 18 touch the other probe to a good ground. Is there continuity? If so, this circuit is shorted to ground. Now put the second probe on a +12v circuit on the harness. This should show an open circuit. If not, this pin is shorted to power.

There is zero possible way on this planet a wire harness 'goes bad'. They don't 'go bad'. They are damaged or they aren't. The wire harness looks as good as it did when I brought it home from the dealer.
Hmmmm.....that goes contrary to my experience. I have seen water get into the insulation of the wiring harness and corrode the wire. The wire looks good, and it used to work fine. After a while it doesn't work anymore. It went bad.
 

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Discussion Starter #7 (Edited)
Outstanding! Thanks a ton! I know that I'm supposed to backprobe. I was staring at my disconnected trans harness at the PCM wondering how to disassemble the back of it to gain access such that I can back probe it. I can probably figure it out but if you have tips that may help me avoid damaging something, I'm open to advice on that.

Also, I attached the PDF of my Transmission portion for Ford's Service manual. Does this help identify the 'return signal path'? Am I perhaps looking for Pin 22 (Page 307-01-2 is Trans connector, Page 307-01-4 is the Trans/PCM Connector). Is Pin 18 and Pin 22 where i need to test resistance/open?
 

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Yes, on the Transmission PCM connector test between pins 18 & 22.
 

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Bump

..... There is zero possible way on this planet a wire harness 'goes bad'. They don't 'go bad'. They are damaged or they aren't. The wire harness looks as good as it did when I brought it home from the dealer......
I can't tell how many threads there are on 6.0L wiring harnesses "going bad". Especially the 04 and 04 model years. quite a few articles from Technician Societies as well. Even Ford TSB's on it.

Wiring insulation does degrade - heat, abrasion, even chemical attack if fluids are spilled or leak.
 

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That is what I do. I use thin probes so that I do not damage the wiring.
 

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Discussion Starter #12 (Edited)
Alright, I am trying to test this connector, but the connectors on my PCm don't match what is in my service manual. In teh service manual "Transmission PCM Connector" has 11 pins across the top. None of my three connectors have three across the top.

I attached my Transmission PCM connector.
 

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Discussion Starter #14 (Edited)

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Discussion Starter #15
Seems to have fixed itself. Nothing wrong with the new sensor, or the old sensor. I took off the connector on the transmission bulkhead to test it. Never could get any resistance readings on those pins but its a huge pain to do that on your back and you can't really see anyway.

Anyway, after that didn't pan out, I dropped the pan again and with all that messing around, the torque app started reading the proper temperature. Maybe the connector on the sensor wasn't just right, or maybe the bulkhead connector needed a little more push. Not sure. Anyway, while I was hooked up to torque, I messed with the wires on the sensor and the bulkhead and never got it to stop reading. I have no idea what the problem was or is. The pinpoint tests on the bulkhead never gave continuity to ground on either pin which is good, even when the sensor wasn't working.

No clue.

How does one change the INTERNAL TRANSMISSION HARNESS on this truck? It looks simple enough to change, but the service manual says to remove the solenoid body first, and I am NOT interested in that at all. Is that necessary? Anyone changed the internal harness on this truck? I don't see any threads that address it.
 
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