On my 2005 Focus 2.0 TDCi I've had a irritating issue for almost two years. When I first start up in the morning, I get a power assist fail warning about 50% of the time. Its not a big deal, I notice the warning on the first turn of the ignition so I turn it back to off, turn it on again and its clear. If I were to start the engine without doing this, I would have no power steering. I've got used to this and just live with it.
Last month I had the r/h headlamp unit out to change a bulb. This gives you access to the power steering pump with its integral reservoir, which according to Ford doesn't need checking or servicing but I always check the fluid level when I get access to it. This time the fluid level was fine but I was thinking that the fluid looked quite dirty. Its been in there for 10 years now. I've got a bottle of the correct spec fluid in the garage so I decided to remove as much of the old fluid as I could with a syringe and top it up fresh fluid.
The odd thing is..... since I did that, the power steering fail warnings have stopped. Its possible I knocked one of the pumps electrical connectors when I was working in there and reset a bad connection but I don't think so.
Could there be some sort of capacitance sensor in there in which the condition of the fluid could make a difference?