Q: Mechanic said OBD P0989 so need to replace silinoid for $1700. Should I try changing transmission fluid first? 2010 Cadillac SRX.

You should ask the mechanic if he actually directly tested the solenoid and, if so, what the specific test results are. If he did not test the solenoid, look for a new mechanic. Trouble codes can never be relied upon as the sole basis upon which to conclude that a part is faulty. All suspect parts must be individually and directly tested regardless of what a trouble code might "suggest". In the case of this particular code, P0989, as is typical with most trouble codes, there are a multitude of possible causes of the shifting fault specifically listed within the code. All of the potential causes must be tracked down using the specific diagnostic decision tree that General Motors publishes in the Factory Service Manual for your specific year, make and model. Did the mechanic evaluate all of the other potential causes of the Code? If the mechanic cannot explain why he is proposing to replace the solenoid, and cannot explain exactly what has failed, or appears faulty in the solenoid, then you are probably wasting your time and money. Obviously, YourMechanic certified mechanics can diagnose and resolve this issue for you, most importantly giving you an intelligible and credible diagnosis. If you want to go that route, please request a transmission shift diagnostic - solenoids/P0989 and the responding certified mechanic will get this taken care of for you and explain in detail what is going on. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.