What does it mean?
The Engine Control Module (ECM) monitors the engine speed through the CKP (Crankshaft Position) sensor with the engine running, and send signal to the Transmission Control Module (TCM) through the J1939 CAN (controller area network) or GMLAM (GM Local Area Network) on GM vehicles. Some manufacturers use a PCM for this circuit. All newer automatic transmissions are controlled by electronic components and circuits. Typical transmission control systems contain many components.
An automatic transmission can be controlled by its own computer, called a TCM or transmission control module. The transmission can also be controlled through either the body control module (BCM) or the powertrain control module (PCM). Each manufacturer has its own design criteria and terminology. The TCM is normally located outside the transmission in a protected, relatively cool and clean location. Some newer transmissions have the TCM mounted on the valve body inside the transmission.
Most electronically controlled automatic transmissions/transaxles use PCM/TCM to monitor the time it takes to complete a shift. PCM/TCM can determine this from the comparison between the engine speed and the output speed sensor data. When a shift is commanded, there should be a change in the speed of the output shaft.
If the change in speed is more than normal, which could indicate normal wear in the clutch pack, the PCM can learn from this and start the shift sooner to allow time for the clutch to be fully engaged. The adjustment is called adaptive control, or adaptive learning, which keeps shift duration within a certain time period. Speed sensors measure the speeds of the input/output shafts in the automatic transmission or transaxle or in this case the engine crankshaft.
NOTE: Whenever diagnosing a 700 series DTC (Diagnostic Trouble Code) with a transmission, transfer case or other driveline components, check for a DTC under chassis and body systems, not just under “P” or powertrain/engine or emission control type codes. Module communications DTCs are “U” codes. These are most often found when looking for DTCs under chassis or body systems.
Chassis related codes are labeled “C” and body system related codes are labeled “B” codes and these can cause drivetrain issues if they affect a sensor that is also used by the heating and air conditioning system. The P0725 Codes is triggered when Transmission Control Module (TCM) does not receive the engine speed signal from Engine Control Module (ECM).