Information kindly supplied by Tendurp
Continuing on with the problem of my Rain Sensing wipers only working at high speed even on a dry day with blazing sun and no sign of rain, I decided that I should get the Auto feature checked out by Mr 'T'. As my car is a November 2009 Avensis, it is now out of guarantee and Mr 'T' would make a charge for performing a Diagnostic check on my auto wipers. When I collected the car from Mr 'T' the worksheet stated 'Checked and reset system all ok'. to my horror the Auto Wipers were still displaying exactly the same fault as before.
In desperation I again searched through messages on our Owner's Club Site, this time I came across a similar thread to this one and a member mentioned that he had, had partial success by unplugging the windscreen sensor at a point behind the central rear view mirror.
I unplugged my sensor thus disconnecting the auto feature, but to my amazement I now have genuine Intermittent Wipe facility. Not only this, but the ring on the stalk that should change the sensitivity of the Auto wipers, now gives me a choice of 4 intermittent wiper timings.