Trans fault light cause

Asked by Nicolas Jun 24, 2018 at 05:52 AM about the 2005 Ford F-150 FX4 SuperCab 4WD

Question type: Maintenance & Repair

Hello dears,
I'm having this problem for 2 years now and haven't been able to fix it. The
truck went to a stop while going up a hill and since then it's been a
nightmare. Transmission changed by a rebuilt one, but still trans fault light
popping up. Trans sensors have been changed by new ones but it changed
nothing. Speedometer and odometer quit working. Speedo somtimes work
while truck fresh started but it means it won't shift properly. Indeed, what is
strange is that if I'm not getting the trans fault code, the trans won't shift well.
I'll then have to turn off the truck to turn it on again, until I get the code and
then have the trans to work almost normal. Brought it to Ford, but they were
unable to fix it. They said there was a problem with a switch inside the trans.
I told it couldn't be since the trans was new and that I already had the
problem before changing it. They went on holidays so I got my car back from
the Sales department who gave me a wiring diagram as a fix. It seems I
have other problems lately since I got also codes P0345 P0349 which added
to previous P0720 and P0171 (which I got only way later the trans code).
Also aftermarketradio is changing channel while driving on a bump and
windows stop working from time to time. I can get them work if I open the
door. Don't if all of this can be related. Please help me before it gets ruined.

8 Answers

830

Wiring. You need to or your dealer needs to trace and make certain that the wiring is solid. No loose connections, broken wires, which it sounds like you have from your description. Dealers have some better test equipment that can help diagnose this. Since you have already changed the transmission, and related sensors, the wiring is the problem. Dont overlook this and dont take no for an answer. If you cannot diagnose this, find someone who can. Not sure what Ford does for computers? Chrysler has a ECM/PCM module that runs the entire vehicle. The tyranny has a solenoid pack for shifting and is connected to that computer. If the communication fails, Chyrsler puts the tranny in 2nd gear and throws the check engine light. Ford probably does something equivalent. If you do this yourself, get the schematic, good multimeter, thin probes, jumper wires. Study the wiring and connectors and plan out where you need to trace.

9 people found this helpful.
20

Hi Guys, Just bought a truck with the same issues on the transmission. Could you share the wiring that was fixed? General location would get me started. Thanks!

2 people found this helpful.
140

Front passenger side check under by the tire that wiring cable/harness didnt come loose. Mine came loose and melted i had to splice and rewire the wires and that was the fix

8 people found this helpful.
40

The window/radio issue is due to a bad window control unit on drivers side. The wiring is all linked together. May also affect your dome lights. Just replace that whole arm unit as it is all one piece.

4 people found this helpful.
290

My TRANS FAULT code will only come on if I am in overdrive. If i have the over drive off only once and a while the TRANS FAULT will come on. Seems to me it might be a speed sensor? Does anyone think it's a good possibility or maybe the fluid needs to be changed? The transmission was replaced because the stock transmission went out with a cracked housing and this one with the TRANS FAULT code is new replaced by AAMCO. I have a warranty on the new transmission but I am reaching out to see if its something I can do myself? What do you guys think?

9 people found this helpful.
10

Do you get this figured out? My 2005 transmission was rebuilt about 3000 miles ago and getting trans fault today. Truck is running fine. Trans fault seems to come on mostly at highway speed and when I brake. Runs fine though.

1 people found this helpful.

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