Q: My 2008 Mini Cooper S has a check engine light on and the code is P0977.

The code P0977 will set if the transmission control module (TCM) records an abnormal voltage reading from a shift solenoid in the transmission. A vehicle with the P0977 trouble code will generally be driveable but due to the potential for further damage the underlying fault causing the code to set should be identified and repaired as soon as possible. Generally, the cause is found to be either a faulty shift solenoid valve; a malfunctioning control circuit; damaged or defective electrical components, such as wires, connectors, and fuses; a low transmission fluid level (obviously check first as such is easy to resolve); dirty or contaminated transmission fluid (if so, would require replacement of the fluid) and; in rare cases, a faulty PCM, TCM, or engine control module (ECM). To answer your principle question, the amount of difficulty in resolving this will depend solely on exactly what the underlying issue is. If the fluid level is low, the cost is close to zero because obviously you can address that yourself. If the solenoid is defective, however, the transmission pan has to be removed and the solenoid, typically installed on the transmission valve body, has to be replaced. The latter repair can typically be performed on a mobile basis though without removing the transmission. If you want this fault investigated and resolved by a certified Mechanic, dispatched by YourMechanic right to your location, please request a shift solenoid circuit diagnostic - Code P0977 and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.