‘05 tdi Glow plugs

I have an ‘05 passat tdi wagon and this morning it wouldn’t start. Air temperature was 4* F. No engine codes or lights on for check engine. But it cranked and tried to start. Bad glow plugs or relay. First time it’s been this cold so I’m not sure if they’ve ever worked since I purchased the car last summer. Just need a good starting point. Thanks.

How long does the glow plug light stay on. Should be 6 seconds below 40F; at least it's that way for the MKIV. In fact the pre glow is ~ 23 seconds if IIRC; meaning you can wait an extra 10 seconds or so after the gp light goes out before cranking. A faulty glow plug should turn on the check engine light. Is your fuel filter full or empty; in reference to the in-tank fuel pump? Should be full.

Search here for the BEW/BHW glow plug fiasco.

You need to find out which plugs your car has in it now, and which software version it has. You may need to update or change something.

It glows for 2 or 3 seconds.

I wasn't sure if the OP's BHW was included in the GP recalls.

The BEW, BHW, and the BKW (the BKW is one of the V10s in the T'reg) are all under the same glow plug saga.