Originally Posted by 2008 ML 320 CDI

I found the cause of the CEL and Glow Plug Light error. It was a very slightly loose earth wire connection to the cylinder head combined with a wee bit of corrosion. Cleaned it up with some sandpaper and tightened the bolt securely and the error code, CEL and Glow Plug light error are all gone! In the end it didn't have to cost a cent! I now have 6 new glow plugs installed when that wasn't the problem.


This earth wire lug to the cylinder head was slightly loose and had a little bit of corrosion causing a poor electrical connection to the cylinder head. Cleaning it up and tightening the bolt cleared the error code, CEL and Glow Plug light error.