PCM Issues

[knightride2005]

2016 Fiesta pulling P604 and P605 and multiple cylinder misfire cylinder 1 and 4, hill assist is off also. Has anyone had issues with this and how did you fix it besides replacing pcm.

 

[SyntheticAtmosphere]

First off the battery needs to be in good condition. Lately batteries are being constructed using more and more recycled material lowering the quality of the internal plate metals. This leads to a shorter service life, batteries dont seem to last 10+ years anymore. Atleast have it tested.
Also ensuring the battery connections are clean tight and in good order.
Good continuity to ground can be ensured by cleaning up and coating a collection of ground wires under the battery on top of the transmission.
The PCM needs a clean constant power delivery as do many other electrical modules in the car. You can experience anomalies when individual modules wont operate properly or when they cant communicate properly from power fluctuations.

Unfortunately it is still possible the PCM is experiencing internal issues and further diagnostic work will be required to verify. The P0604/P0605 codes are not common. There is a possibility an update could be in order, however I experienced a P0604 on my wife's Mazda a couple years ago. The PCM was bad and required replacement...luckily under warranty.

 

[Handy Andy]

Since it's a 2016 - the "multiple misfire" can also be mileage related or any current issues of water entry into the system.

The Spark plugs if you haven't changed them, this is year 8 on those plugs - a long time in interval - so you might want to think about getting this looked into.

What turns off Hill assist is from the system thinking it has "power delivery" issues. So this may be a kind of thing I would call - a type of rust and corrosion problem - the Oxides of March - where one season melts away and a new one floods into every nook and cranny and steams up your windows - requiring you to use nearly all the functions your vehicles Climate control can muster in just one month from Winter to the Spring and prepares for Summer heat.

So if you haven't already - review your service records and how long has it been since you've owned the car and even the belts and hoses, the radiator fins and the battery - might need a good cleaning at the local coin-op car wash to remove crud collected in the engine compartment since the last time you opened the hood.