2003 1.9d problem and I just can't understand it. Travelling along at 50mph with no prior warning and the yellow eml light came on with a loud diesel Knocking noise. I own a basic OBD code reader so when I got home I plugged it in and it says NO CODES. The light and accompanying noise have been intermittent. Today it was knocking but I had to use it for work. I stopped on a sideways ( left ) slope and immediately the light went off and knocking stopped. The van ran fine for ten miles then it started knocking again. Help please. I am no mechanic but I can turn a spanner.

try changing fuel filter, and put some diesel cleaner in your tank, fuel filter might have some crap in.

Sometimes, it's (a) worn injector(s), spraying to much fuel at the false time, causing knocking sounds...

Thanks, I'll certainly give that a try first.

Update: van went for MOT with knocking engine but no probs with emissions, which was good. I suspect the glow plug relay is faulty. It seems warm, the centre wire underneath appears wobbly as if plastic has melted. There is a black plastic item attached to the top of the fuel pump, removed by undoing two torx bolts. I undid item and lifted it off, then started engine. Result = knocking stopped. I refitted item and so far engine now runs normally. Question is...why?