Glow plug light coming on. Clio 1.5 dci

Hi, I have a Clio 2005 1.5 dci which normally runs really well and is very good on fuel. However, occasionally the glow plug light comes on and it loses a bit of power. I connected an OBD2 code reader to it and got two error messages.

1. Throttle/pedal position sensor/switch c circuit.

2. Glow plug control module control circuit/open.

Has anybody got any ideas what the problem could be?

Thanks in advance.