Transmission wont shift on it own

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your 900. If your transmission shifts fine manually but won't shift automatically, it's often related to the transmission control system. Common culprits include a faulty transmission control module (TCM), malfunctioning shift solenoids, or a throttle position sensor (TPS) issue. These components work together to determine when the transmission should shift. If one isn't functioning correctly, it can prevent automatic shifts. Electrical connections or worn wiring could also cause this issue, especially on a vehicle of this age. I'd recommend testing the TCM and solenoids and scanning for any fault codes to pinpoint the issue. Once the source is identified, it may be a straightforward fix. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!