Hey all, been a while since I've been here, been through several cars over the years and settled on a 2018 Focus ST Line X 1.5TDCI and a 2020 Puma ST Line X 1.0 (his and hers)

For a little while now, the Focus has been throwing up the Hill Start Assist Unavailable and Transmission Not in Park fault, sometimes it comes and goes, often with months between flare ups. I've been doing some research before starting this thread and ruled out poor battery voltage (new battery installed a couple of months ago and showing perfect SoC and perfect voltage when off/idle. Start/Stop works fine, always has done.

Initially I had it down to potentially loose or exposed wiring somewhere as it seemed to appear most when it was wet or I'd just cleaned the car... But, it's been relatively bone dry in the UK for a few weeks now, and it's flared up again, with a new symptom - the auto transmission keeps shifting itself into Park, and the wife worryingly reported that the brakes completely failed to engage at all whilst driving, and it took the collision prevention system to kick in for the car to stop yesterday... It was serviced a couple of months ago and the rear discs and pads were replaced as they were cooked, but up to now, no problems with the brakes themselves.

I have FORScan and had it hooked up, and it gave me a couple of error codes;

U0404

B146D

P166B

I know this links back to the drivers side door latch mechanism and I'm looking into getting that replaced, however, it's the transmission shifting itself into Park which is concerning me. It happens pretty much every time the car is started and, thankfully, only at low speeds < 5mph, but it can't be good for the gearbox...

Is there anything more sinister at work going on, or is it a safety feature of the car detecting potential door open issues and stopping the car?

Early MK4s had terrible software glitches and conflicts between modules.

And yours is very early.

I would take the hit, book into Ford and update every module available.