Seat Ateca Diesel Engine Issue

That sounds familiar. I had a similar issue with my Ateca: preheating light staying on, engine light, and smoke when accelerating. First, check the glow plugs. Given the mileage, I'd also suspect the glow plug control unit. Have you had a diagnostic test? What codes showed up? When was your last car maintenance?

The diagnostic test showed a 'glow control unit defective' error. I read the error code using an OBD reader. Is it easy to check the cable or plug connection myself, or should I take it to a workshop? I'm reasonably handy, but I don't want to mess anything up. The car maintenance was done a couple of months ago.

A 'glow control unit defective' error points to that unit or its wiring. If you're seeing smoke, confirmed the error code, and the maintenance is recent, I wouldn't do too much yourself. A faulty glow plug or control unit can cause engine misfire, especially during a cold start. Checking the cable and plug connection is simple, but a damaged cable might not be visible. Take it to the workshop; they can properly diagnose the issue and replace the unit if needed. It might save you from causing further problems.

Just to let you know, it was a bad connection on the glow control unit. The workshop cleaned the contacts, and now it runs great. Cost 95€ total. Thanks for the help.