I had same problem. But basically get a 1/4 inche deep 10 mill socket and a racket. Uncap the cabels to the glow plugs. Carefully take out first glow plug. connect the glow plug to your battery using some wires (I used the wires on my multi meter, put the glow plug against one of the battery terminals and using a wire to connect up to the other one). The plug should glow red hot, within seconds (obviously be carefull). Repeat with all the glow plugs. What I found is one of mine just got hot but didnt glow. I replaced it for one someone recomended (from ebay, it was a demso one i think or bosch) and this glowed when i test it. Put them all back in and the error cleared. I think most likely you have the same problem as me. It took only a few minutes to fix and the plug cost 9 pounds.