u140000 fault code mk3

Yesterday i was driving on the motorway on a hot day with a lot of stop start traffic.

Near the end of my journey i saw the EML and 'coil' symbol appear on the dash. I've never seen either before.

The car went into limp home mode with some power but very much restricted.

I pulled over, turned off the ignition and ran my OBD scanner. It picked up a code of u140000 which appears to be a potential electrical / alternator fault.

The manual seemed to suggest it could be a glow plug fault but then I've seen other info online saying the "coil" error which appears to be a glow plug error is actually a few different faults when combined with a check engine light.

After scanning the fault, clearing the codes and restarting the car I've not had any further issues.

Last night i read that it's sometimes a MAF sensor that triggers this fault so this morning i changed the air filter as i haven't had a service yet this year and I'm not totally sure the garage did it last year during the service (i usually do the servicing myself.)

Drove home tonight at 70 with no issues.

At times I'm getting the dpf notification but it appears to clear and I've not so far had the proper dpf errors.

Has anyone had this error or can shed any light on this? I've replaced 3 out of 4 glow plugs fairly recently but struggled to remove the pressure sensor glow plug so far and so this is the original at 120k+ miles.