I had local auto parts store scan for error codes since check engine light came on 1 day ago. “glow plug circuit” is what scan read. Is that just a bad glow plug and do you change all glow plugs at once? 172K on a 1999 E-300 turbo diesel.
Did you get the actual code Format: [P1234] ??? It should show up what glow plug or plugs appear to have a problem. If my glow plugs had 172K (just a bit over 100,000 miles I would replace them all. It is time and they are not that expensive. I don't know how hard yours might be to get to. On my car they are all easy to get to. Make sure you clean the contact area from any contact areas that are disconnected.