I have been having a problem lately with my transmission temperature sensor going high resistance according to the PCM/TCM, and I believe it is in the module itself. Will you all please tell me if you concur?

What's happening:

This seems to revolve mostly around bumpy roads or inclines. It is most easily repeatable by tapping on the connection of the transmission harness to the PCM/TCM (the one closest to the front of the truck.) It will surge to 8000+ degrees or back to normal, and that is the way to clear it.

Why I think it's the PCM/TCM:

Tapping on the connector and 'jiggling' it around can bring it back into working order. I pulled the battery basin and rerouted the cable a bit nicer so it wasn't being pinched and when I did that I pulled off the covering well past that are and only found minor pinching, but nothing which looked damning.

I have also removed the cover on the connector, and don't find anything that looks wrong in there, no wires were loose or exposed, and all of the pins look to be in good condition.

What I believe is the root cause:

I am going to assume that there's probably a solder or capacitor which has decided to start misbehaving - is this a common problem with the PCM/TCM?



Does this seem possible enough to justify buying a new PCM/TCM or am I just stupid?

 

The TorqShift has had a lot of failures of the transmission temperature sensor. It is located inside the pan. It would be highly unusual for your problem to be the module instead of the sensor.

 

I forgot to mention that I have already replaced the sensor...

 

I would verify the wire is not broke further down the harness. Remove it and open up the armaflex and make sure that wire is not broke or chaffing any where.

Sent from my leash using IB AutoGroup

 

I did that as far down as just below the degas bottle, and aside from some pinching in the yellow/green wire, which didn't seem to effect it (flexing at the pinch points didn't cause the temperature to cut out). Is it possible that it is further still, considering tapping right at the harness will cause it to cut in/out?

How difficult is the wiring harness to replace? It looks easy, but some of the clips I can't see. What would shop time on that be, and what is the part number so I can perhaps order a new one as a final elimination.

 

Use a ohm meter and a helper. Find the pin on the plug going into the Tranny on the harness and ohm to the pin on the harness at the pcm. Start wiggling and moving the harness and see if you loose continuity at any time.

Sent from my leash using IB AutoGroup

 

Ask Miles aka acf6 about that headache.
Not any love on his bank account.


Sean

 

I found in the 06 diagrams and I see you have a 05.

From looking at the wire diagram and the connector
diagrams. I see that it looks like the TFT only uses 1 pair
of wires. You could do some testing on the wires and
see if you can find the problem. The other option is it could
be a dirty pin on the plug at the transmission or at the PCM.
You said the problem shows up when tapping on the transmission plug?
If that is the case I would start by looking at that plug and all it's
pins and there mating sockets. One thing to not do unless you have a
dummy pin is stick the probe of the multimeter into the mating side
of a pin. You can open the female side up and cause it to be loose
and not get a good connection on the pin when they are together.

The best way to test is by back-probing the connector. You are going to need
a very low range ohm meter to see what the resistance of the wire is.
You could make something to use in it's place if you don't have access
to a low range meter. When I am saying low range I am talking 2Ω ~.005Ω
But how ever you look at it you should see see less than 2Ω
1000Ft of #18 copper stranded wire is about 6.3Ω and
1000Ft of #14 copper stranded wire is about 2.5Ω
I would think that 15 feet one way would be more then enough
wire length. This is if the wire is full copper and not some other
mix. So 2Ω may be ambitious on my part.

But I still am thinking that you have a corroded connector for the
problem after you said that you have replaced the sensor that Mark
said was problematic and that you have fund tapping on the connector
changes the readings.

The sensor is using Vref to power the sensor and any corrosion on
the pin or socket will give a false reading.

Let me know if you want me to come down with the really odd electrical
tools. I don't charge by the Hr but by the gallon and motel costs


Sean

EDIT : Maybe we can get more input from Mark on this.

 

No, probably not. I already stated what I believe the problem is. It's been ignored. I see no reason to change my opinion with no new facts.

 

It wasn't ignored. OP stated the sensor was replaced.

Josh

 

What is the rate of new sensors being bad out of the box?

One question I should ask first. Was in and OEM sensor or and aftermarket one?


Sean

 

Oops! Sorry, I missed that post.

If it isn't the sensor, it almost always the wiring between the sensor and the PCM. It is very, very rarely the PCM.

 

Will do that this coming weekend (spent today working and tomorrow BBQing - frigging wife not realizing Father's day is the day that fathers don't want anything to do with anyone for any reason...) I have a p.cal which can accurately go to .001 ohms which I frequently use on high precision circuitry, and I regularly rail on people about using the correct leads, so I appreciate you doing the same!

The corroded connector I can buy, because taping on the connector at the PCM/TCM side seems to be the only thing that makes a difference - not moving the wire down the line where it was pinched, or anything else that I can easily replicate. The fact that it is a thermistor instead or an RTD or Thermocouple is why I was thinking possible circuitry issues. I assume there is nothing special to worry about when using CRC or some similar electric-circuitry cleaner? Anything I should worry about with the materials before spraying some dielectric grease in there?

Doe anyone know the pins and/or the coefficients if I decide to side-tap into the wires while running? (I am going to google a bit to see if I can find the pin-outs.)

I am not ignoring you, Mark - that would be dumb of anyone to do given your intimate knowledge of these transmissions. Since you are more in tune with the subject, what is the likelihood of getting a bad sensor from the factory (Motorcraft, of course.) I can understand infant mortality in hardware, but I am just thinking based on where I can most easily repeat the problem that I would prefer to attempt troubleshooting there before pouring another $100 of fluid and a $30 sensor in there. I did enjoy using this opportunity the first time to install my 08 filter and pan.

-Quick side-line: Did the magnet placement have any significance on the pan? I moved it so that it was around the drain plug, since it is lower in the pan. When I got it, it was up near the top on the side, opposite the drain plug.

 

Funny that you should ask for pinouts.
I create the 06 diagrams in PDF form.

BTW I have 2 sets of Wheatstone bridge tools for aircraft use.

Do I understand it right that when you tap the connector at
the PCM that you get the change?

I was thinking that the plug down on the transmission would
be a good place for a fault. But up at the PCM right next to the
battery would expose it to any leakage/gassing from a battery.

On the leads issue. I watched a guy on Youtube explain how to check
a glow plug with a dmm on Ω and he had his fingers on the probes
2Ω not so big a deal. But it's always best to use best practices all the time.
You never know when some high voltage has gone astray.

Sean

Fun with Smilies

 

That sounds like a really big clue to me. Replacing the connector should be your first priority.

No, that will be fine.

No, that was my fault. I missed the post where you said you changed the sensor.

Not likely. Don't change it again. From what you have described above I'm betting on the connector being the problem. This is a very low current circuit and a very small amount of corrosion in a connection can create this problem.

It may have. I wasn't involved with that, but in general the magnet is placed where there is enough room so it doesn't contact the valve body or the filter, and in an area that has some circulation. There are dead spots in the pan where the fluid tends to stagnate.