Our 2016 S-Max Titanium Sport, will randomly change down gears, the display goes from D to S and then the numbers can go down a gear at a time, if you hold the right paddle down,(constantly)  it drives perfectly and doesn't change down anymore!  Almost like its receiving an erroneous signal to change down.  Other than that it drives great, the gear changes sound normal and are smooth.

To fault find:

New battery

TCM and PCM low voltage codes via Forscan, once cleared didn't come come back. 

Car died whilst driving, alternator was faulty, once replaced drove perfectly for around 2 months (with the gear change issue resolved), then suddenly its come back.

Ford say it could be the gearbox after their diagnosis couldn't find anything.

Powershift gearbox experts say it's definitely not the gearbox (drives perfectly when not at fault or with the paddle in)

No further or new fault codes.

I suspect an electrical problem and still something to do with power!

 

Has anyone had anything like this before and could offer some advice (happy to pay someone for the correct diagnosis, as it's absolutely doing my head in) 

 

 

 

As you say, it does sound like a signalling issue and I can only give this link to consider, that deals with a similar problem - no gears at all. It was an electrical issue needing a detailed (but not rocket science) fault find involving load testing of wires.
Your problem may be a short circuit, suspect the paddle switch (?) giving erroneous signals, or not?:

https://www.youtube.com/watch?v=ikDCVb93mk0

Of special notice are the multiple fault codes many of which are totally divorced from the actual fault?

I'd personally disconnect that paddle switch and see if the fault disappears as a first option?
I absolutely hate it when, with no justification at all, they say "It may be the gearbox" - all best ignored and fully justified diagnosis carried out that can then give you the options.
My local specialist will refund you if an incorrect part is fitted:
https://intelligentauto.co.uk/services/fault-finding/

Get a decent vehicle electrician to test the continuity of EVERY cable from the transmission to the TCM and from the TCM to the PCM.

You will find you have a broken/braking or corroded wire somewhere.

Also, make sure the gearbox is earthing correctly

Although holding the paddle removing the fault is also needing some priority in the wiring investigation alongside the under bonnet work?

Is there a PID for the paddle position that can be monitored?

 

Great replies and thanks for taking the time 👍

Since then I did get the following faults:

 

===PCM DTC P0626:13-6C===

Code: P0626 - Generator Field/F Terminal Circuit High

Additional Fault Symptom (:13):

 - Circuit Open

 

===PCM DTC P0625:14-6C===

Code: P0625 - Generator Field/F Terminal Circuit Low

Additional Fault Symptom (:14):

 - Circuit Short To Ground Or Open

 

I still suspect this to down to the charging circuit somehow, even after a new alternator and battery, I think maybe a bad connection between the battery earth or to the alternator, will inspect over the weekend and Vaseline up etc.

Interestingly after driving around with the paddle held in for around a week (drove perfectly fine), the cable tie came off 😀 and now there is no issue whatsoever!! So strange

Voltage high, then low so at the moment, I'd do the same as you (although may be further back in the loom)

Paddle issue may be intermittent fault so again, is there a Forscan PID for its position so that the the fault comes back giving paddle OFF  but ECU says its DOWN or something?