On-board diagnostic (OBD) systems are installed in most modern cars. They are made up of sensors and a computer. The sensors relay information about how a car is running, and the computer analyses the data received and outputs it in the form of a OBD code. The code, PO727, relates to a lack of data being received by the OBD computer.
The P0727 code is a universal code, so it is used by most manufacturers, including BMW. Its technical description is "Engine Speed Input Circuit No Signal," caused by a lack of data for the engine speed input circuit.
Engine Speed Input Circuit
The Crankshaft Position (CKP) sensor monitors engine speed, sending its data to the Engine Control Module (ECM). The ECM sends this data on to the Transmission Control Module (TCM). Code P0727 is the result of the TCM not receiving the signal from the ECM.
The cause could be a fault with the CKP sensor and its circuit to the ECM or problems between the ECM and TCM. In the first instance it is worth checking the electrical connections on the sensors, ECM and TCM for damage, moisture or dirt.