My Mazda 323F engine stops just circulating

Hi, I'm hoping someone can help me. I have a 2000 Mazda 323F, and the problem started about six months ago when the engine stalled while I was driving on the highway. I pulled over, restarted it, and it ran fine. It was fine for another three months, and then the same thing happened again. Everything was okay until two weeks ago when it stalled about 20 times in 30 kilometers.
I'd like to know what you think it could be, as the garage says we'd have to replace the diesel injection pump to test it, but it seems like too expensive a repair just to test it. I've been reading something on other forums about the injection relay. Could you help me? Thanks.

Look, you can test the pump by measuring its pressure, and that's it. Something very similar happened to me with a Suzuki Grand Nomade. I removed the thermostat and the problem was solved. I don't know what the cause was, I just know it was fixed and I'm still tinkering with it. I also did it with a Corsa that had the same problem. If it helps, as soon as I discover these blessed problems, I'll post them all.

Thanks, I'll try what you suggested and see if I have any luck with that.

Did it give you any other problems besides shutting off? Did the check engine light come on? Any detail could be important, because it's strange that it was fixed by removing the thermostat, my good friend kikemec. It's a case worth thinking about. Well, greetings.

The low fuel light in the diesel tank comes on occasionally, even though we drained it following the manual's instructions. The airbag warning light also flickers occasionally. I don't know if it's related, but otherwise, the car stalls without warning. It's not related to the engine speed; when it stalls, it just stalls.

I've been reading something about the fuel injection relay. Do you know where it's located in the car? It seems easy to check.

Thanks