Ok I have looked far and wide on the internet..... At a fresh start-up the truck will not shift into fourth, BUT after driving around a while the Service Engine Soon light comes on then fourth and OD starts working. This continues until the truck is turned off and when restarted (even seconds later) the cycle starts over. This has just arisen suddenly and the code came up as a brake light switch, which has been changed with a new one. Any ideas? thanks in advance!