[bmw335d]

I got an intermittent glow plug error for one glow plug, what's the implication of not fixing it?

[335dlci]

A very very very hard start. Mpg.

[kbsilver]

Glow plug errors are "usually" the glow plug controller, a DIY repair. The controller is known to fail, seems typically around the 100K mile point, while the glow plugs themselves are close to bullet proof.

I had a glow plug #5 fault and the car started and ran fine (fault cleared by changing the controller). You will have starting problems during very cold weather or if you have multiple glow plug issues.

[Spyro235]

I started with a #5 glow plug fault, but then it progressed to include #2. I started it all winter without 2 glow plugs. It had a miss on soaked cold starts(overnight in below freezing) but it would clear up within 10 seconds most of the time. What it was REALLY cold, like cold soaked in -10f, it might have that miss for up to a minute after starting. If all the plugs go out, you'd probably have a hilariously rough start.

I had done a lot of reading, and figured it was jsut my controller, since I was forced to drive about a thousand miles with a really, really bad thermostat. My coolant barely hit 60C, and that was while towing.

The controller is a DIY. A frustrating one on an X5, but it's frustrating, not hard.

Nothing bad will happen if you let it ride. You'll have to live with the check engine, and in my opinion, should check for other engine codes every week or two just in case something else pops up that would have triggered the light, but that's pretty rare anyway.