Transmission goes in and out of Overdrive on it's own, most of the time @ 50 MPH.Replaced sensor, replaced harness what's next?
Have a ford tech drive it at your dealer. defining the symptom can stop the unnecessary parts replacement. Then when he verifies and defines it. he can isolate with the tests if you authorized. Normally the first hour can contain the road test, testing and get you the cause.
My problems with the tranny shifting into and out of O/D at low speeds was greatly reduced to the point of only once in a long while by replacing ALL the tranny fluid with Royal Purple Synthetic fluid....as another benefit, it shifts harder and is very consistent. My whip is an '04 P71
Contamination or build up can mean time to service or flush. The vehicles supplied manual is supposed to advise gear selection, for terrain. the best use of overdrive is described there based on what they recommend for that trans in that year. A trans builder is the best person to talk it over with to save it. He tears them down and knows what fails, and after what the customers habits were.
A torque converter issue can be considered during the discussion. Flushing and additives for grip or antishudder could be help in some circumstance
If the tech uses the NGS and captures the data during the event, and the method of gear selector choice is correct for the conditions, The data can reveal any electronic issue. The PIDs can be recordrd for playback. That means you can watch each datastream circuit as the trans performs or has its "hiccup" Then get it explained, get recommendations, or effect repairs. Sometimes this leads to service bulletin info that can help. It Always depends what it is and whether the info actually applies to the year, make, model, and situation. A FORD service area often has one trans builder who devotes his "life" to this knowledge, experience, and current data as well as his own Ideas that develop from trying to effect economical repairs.
If an older vehicle has issues with the overdrive cancel switch, it can be caused by the tilt being operated back and forth or overmaxed over its life. there is a repair you can make But you must know by testing or inspecting yours. There may be a bulletin found and a motorcraft corrective repair kit available. The idea being broken wires where it pulls or pivots. I watched a utube where the guy has a failed trans and an o/d light issue. it was on a pickup, but it stands to reason that the car platform having similar column shifted design can have likely same issue.
I think the tailshaft mod and the J-Mod would take care of 98% of the maladies in our trannies....a convertor would be an 'ultimate' mod to me, can't wait for that day
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