Odds on it's a one way valve, so after looking on WIS and EPC I didn't really get a good view of the components involved. Then I had a bright idea. I should have one off the breaker. Found it, tested it, one of the one way valves has failed, I can blow from the manifold end all the way to the T7 valve
As I didn't want to have wasted my time getting this out, I thought it was time for a picture and a schematic
The valve that has failed on this pipe is the one on the left. Exactly what I think has happened to the green car. Do you agree ?
I am relieved that I didn't remove the pipe from the car first.