The regen temp should be 600 deg +
Relay 4, on stage V cars switches the vaporizer glow plug. Test by substituting with another. Fuse is F6, check contacts. Yours is stage VI though?
The vaporizer is fed fuel from a pump. The pump is controlled by an
ecu using pulse width modulation, I google 4Hz and ramping up. I don't know how to test it.
If the vaporizer is fully blocked a vacuum tester will hold vacuum. If partially blocked
it's more difficult to assess, and will need to be removed for inspection.
So I gather googling.