When the ignition is switch to the RUN position the TCM performs a functional check of the solenoid valves, switches and sensors. If a problem is detected in any of the inputs to the TCM the TCM will enter limp home mode. This allows the operator to select the gears manually regardless of vehicle speed. Care should be taken not to downshift and cause the engine to over rev. The vehicle should be taken to a repair facility as soon as possible to avoid driving while in this mode.