I often use steam trains on TSW4 and for whatever reason it does a service failure, I have steam firing on Automatic and it still leads to a service failure.
I had/have the same issue on Xbox, I haven’t used them since then, I tried about 3 services when I got Peak Forrest in December with the Jubilee class, firing on auto and just before the last stop there was a sudden service failure on each. to be honest after 3 in a row it kinda felt the entirety of steam was completely broke and I haven’t used it since cause of that mostly.
Bit of a bump on this one... Was doing a run with the Jubilee on SoS just now to advance the Journey Mode. Had resumed from a save game but in Manual Firing Mode yesterday no issues as I had used Ctrl - F to open the firebox doors. After loading back into the run this evening, going for about 5 minutes then up came "Service Failure" and the scenario terminated. So it looks either as if post TSW5 the save game is no longer saving and restoring the firebox door position, or there is some other bug at work. I know DTG don't want to revisit steam and get their hands dirty but this needs looking at. I mean to be honest, bearing in mind there is no visible consumption of coal either in the firebox or from the tender, why not just scrap the condition that failing to open the firebox will cause the fire to go out. It's effectively an eternal flame linked to an eternal fuel supply.
Please disregard the above. User error. I was hitting Ctrl-F and of course the firebox door command is just plain old "F". I shall retire to the corner and put the dunce hat over my senile old brain...