Our van keeps going into limp mode - what's the issue?

We have a Nissan Primastar. It has only just had a service but the following problem was pointed out to my mechanic. The glow plug and service light comes on after about 3 miles of travelling, then goes into limp mode. He checked (diagnostic check) and couldn't find what was causing it. It's my everyday van and a day camper, so it's needed on the road. Also, my headlights are pretty random, they come on when they want to, maybe it's this?
Usually, a diagnostic check would have shown up a fault code to indicate where the problem lies. Given that the glow plug light is showing (which in turn can result in the engine going into limp mode) we would concentrate on that area. The mechanic should be able to test the glow plugs and also the circuit to see if a fault exists and replace as necessary. As for the headlights we would suspect a faulty/ loose connection (could be at the switch or fuse box). Again the mechanic should be able to check this but the headlight problem is not related to the limp mode fault.
Answered by Alan Ross on

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