Bio1213 said:

I believe that if any warning lights are illuminated then its now an MOT failure?

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Constant lights.
Airbag..ABS : fail

A flashing GLOW symbol may well be just 'advisory'..
Some of this is down to the tester on the day..

Bio1213 said:

I believe that if any warning lights are illuminated then its now an MOT failure?

Click to expand...

This myth was widely circulated in the press a couple of years back but is not true, although there is now a growing list of lights that are checked.

Only certain lights mean a fail (and note that it can be lights that don't come on too - eg main beam light or rear fog warning must show when turned on, and the tyre pressure warning light must illuminate when the key is turned)

The only lights on that will fail are "The MILs [malfunction indicator lights] or dashboard warning lights will also be checked for the ABS, ESC, electronic park brake and brake fluid warning lights.", and the MIL for seatbelts and airbags, and for failure of electric power steering. - see https://www.gov.uk/government/publi.../car-parts-checked-at-an-mot#more-information

Thank you thats good information.

Prompted by comments in this thread, I changed my one failed glow plug today. Turned out to be easy - but maybe I was lucky! See https://www.fiatforum.com/threads/changing-a-glow-plug-easier-than-led-to-believe.493831/ for photos and details (a sort of 'how to' guide). Note - unlike comments in this thread, the spanner/socket needed is 9mm, not 8...

@lambou1d