What does it mean?
The TCM (transmission control module) calculates gear ratio based on data from the transmission input shaft speed (ISS) and output shaft speed (OSS) sensors. The TCM compares the calculated gear ratio to the known gear ratio for each commanded gear. If the TCM detects an incorrect 1st gear ratio while decelerating in LOW (L), indicating no engine braking within the transmission, then DTC P0730 sets. DTC P0730 is a type A DTC.
This DTC monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows: Torque converter A = Output shaft revolution signal from speed sensor (OSS/VSS) B = Engine speed signal: CKP (Crankshaft Position) sensor from ECM/PCM C = Gear ratio determined as gear position which TCM want it to be in If the actual gear position is higher than the position supposed by TCM, the slip ratio will be more than normal.
In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction. 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. DTC P0730 TCM (transmission control module) has detected that the transmission is trying to mechanically shift to a lower gear than intended.