Thanks to Darren for the wiring diagram and operation details which proved to be essential information. There appear to be 2 supplies to the solenoid from the ECU, one of which has a resistor built in to the loom. I will carry out the checks on the circuitry again now I have the correct information and see if I can get any further with a solution to the problem.
Many thanks for your help Darren I will post again once I have some answers.

Roger