I have a 999hd si Hummingbird. My temp sensor is not working so I was told by customer service to plug it in to someone else's unit to see if its the unit itself or the transducer thats bad. Any model in the 8 or 9 series should work for a quick test..I just don't know anyone that has 1. I live in Hilton and if anyone around the area has a humminbird that I can plug my unit into for a minute it would be much appreciated.