FSX Steam Edition: NAV radio won't capture ILS (no ident tone or purple diamonds)

Glad you got it sorted — and that fix actually makes more sense than it seems

What you did (clearing the NVIDIA DX shader cache + a reboot) can definitely “unstick” weird display/rendering issues in FSX:SE. The key clue is that you were missing both the audible ident and the localizer/glideslope diamonds. The ident tone is radio/nav logic, but the on-screen needles/diamonds are also a gauge/rendered UI element — if the sim’s DX pipeline or cached shaders get corrupted, you can end up with very odd one-off symptoms that look like “NAV stopped working” when it’s really the avionics/gauge display chain misbehaving.

If it comes back, here’s a quick checklist I’d run before ripping anything apart:

Quick ILS sanity checklist (when it fails again)

1. Verify you’re tuned to the published ILS frequency (some airports have multiple runways/ILS variants).
2. Confirm the NAV is in NAV mode (not GPS). Some default aircraft will happily show “NAV” on the radio but still be tracking GPS for the CDI if it got toggled.
3. Make sure the correct front course is set (some panels behave oddly if the OBS/course is way off).
4. Try swapping NAV1/NAV2 (tune the same ILS on the other radio) to see if it’s specific to one receiver/gauge.
5. Test in a default aircraft at a default airport as a control (rules out an aircraft panel issue).
6. If visuals are missing again (no diamonds/flags acting strange), do exactly what you did: clear shader cache + reboot.

One extra “preventative” note
If you recently updated NVIDIA drivers around the time this started, that’s often when shader cache weirdness shows up. Clearing it once usually fixes it for a long time.

If you want to pin down the cause in case it happens again: which aircraft were you in when it failed (default 737/Baron/etc or add-on), and did it happen at all airports or only certain ones?