What does it mean?
Years ago, the automatic transmission was simply controlled hydraulically. However, much like the engine itself, the automatic transmission has been significantly upgraded, including electronic monitoring and controls for every aspect of upshifting and downshifting. Today’s automatic transmission, up to ten speeds in some cases, can shift as smoothly or as powerfully as the driver demands, all while reducing wear and maximizing fuel economy and performance.
BMW 8-Gang Automatik-Getriebe BMW 8 speed automatic transmission Keeping track of the automatic transmission is the transmission control module (TCM), which may or may not be integrated in the engine control module (ECM), depending on vehicle. The TCM shares a number of signals with the ECM, such as engine speed (rpm) and throttle position (TPS), as well as a number of other signals, such as vehicle speed (VS or WSS), gear position, shift lever position, and shaft speed sensors.
Using this sensor information, the TCM activates solenoid valves related to such automatic transmission components as clutches, brakes, torque converter lock, or pressure regulator. If there is an automatic transmission control system fault, a transmission-specific DTC (diagnostic trouble code) will set in the TCM. Since there is no “Check Transmission Light,” the ECM sets an informational DTC P0700 and illuminates the MIL or CEL (malfunction indicator lamp or check engine light).
Since DTC P0700 simply refers to a fault in the TCM, further diagnosis is necessary to determine the TCM DTC and the nature of the fault. Some scan tools may or may not be able to read TCM DTCs, depending on whether the automaker has opened them up to generic readers.