Reading further I have just discovered that socket 6 might have a function too, so have tried it and come up with code 1-4-4. This is not listed in my Haynes for a Jetronic 2.4, and if an EZK it makes no sense at all because the symptoms should be no-start or erratic running, and in fact it has continued to run fine.

I have succeeded in resetting the unit using socket 6, and the light has gone out and so far stayed out. So it seems that whatever it was has cured itself.
I'd like to know though in case there is something I should be checking.

I don't think I have the odometer mechanism others describe - I think after 288,000 miles a service reminder light is a bit overdue.

Thanks, but still puzzled.