Q: How do you check and fill a transmission on a 2005 mercury mountneer

Unfortunately, your car does not have the old style dipstick access and so it is really involved to change the fluid. Drain and refill on this model requires the following tools: Rubber Tip Air Nozzle (100-D009 (D93L-7000-A), Vacuum Pump Kit (416-D002 (D95L-7559-A), Fluid Transporter/Evacuator/Injector (307-D465), Adapter, Fluid Level and Fill Plug (307-437). Although there is a drain plug in the pan to remove the fluid, new fluid is added under pressure (30 PSI max.) using the above referenced adapter and fill plug and pressurization system (aka, Transporter/Evacuator/Injector system) through the smaller access port in the center of the drain plug. The whole process has to be done with the vehicle very level, that is on a hoist or, if using jack stands, about 2 feet in the air to gain sufficient access. To check the fluid level the same tool set is required and there is a rather complex procedure that is followed also using that small plug access through the larger drain plug. Normally, transmission fluid is not lost and so unless you see clear external evidence of transmission fluid leakage, the fluid level will not have changed since the factory fill. Adjustment of the linkage is a ten step process and also implicates the transmission range sensor adjustment. It would be unusual for the linkage to be out of adjustment, particularly if the vehicle has less than 100,000 miles. If you desire that the transmission fluid level and condition be inspected and, if you have concerns regarding the shift linkage, due to the complexity of these particular repairs, it is highly recommended that at least the first time you do them, you seek a professional to work with you. If you desire, YourMechanic can dispatch a certified Mechanic to your home to perform the transmission fluid inspection and service and also address any other concerns you might have.