Fail Safe Mode comes up on the dashboard whenever I press the gas pedal. The car won't move until it gets to third gear. I pulled the codes and got error code P0720, which is Output Speed Sensor.
The output speed sensor is a very important sensor for the computer in your BMW 540i. It uses this signal to determine shift points as well as when to lock up the torque converter. If the computer detects a problem with this signal from the speed sensor, it will default into limp mode to protect the engine and transmission from any potential damage. In most cases, the sensor has likely failed and will need to be replaced, however, occasionally there may be a problem with the wiring. I personally have witnessed a plug that was disconnected from the sensor and just needed to be plugged back in and secured to the sensor.
To be 100% certain, I would recommend enlisting the assistance of a certified mechanic to come by and inspect your BMW. They will have the experience and tools needed to quickly identify the cause of your symptoms and perform the repairs needed to get your BMW driving smoothly again.
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