My 2000 jetta tdi has the check engine light and is stck in limp mode. It is starting to start a little harder and also my glow plugs don't come on when I turn key on and I have to cycle the key over and over until it fires or sometimes it doesn't start at all for a while. Is it the glow plugs or the harness that is causing the problem or could it be something different? Would it even help to replace them it does have 220000kms and I doubt they have ever been replaced. Please help I don't want to dump a bunch of money.