2004 Smart Fortwo P0702 Code: Transmission Control System Electrical Fault - No Start After Gearbox Sync Failure

Hello everyone, this is my first post on the forum and I really appreciate any advice or insights. I own a 2004 Smart Fortwo that has been running well for years—except for occasional issues when shifting into 6th gear. The car would sometimes display the '3 bars of death' warning and fail to start. However, disconnecting the battery for a few minutes would reset the system, allowing it to start and drive normally as long as I avoided using 6th gear. Recently, I took the vehicle to a certified Smart Car specialist to re-sync the gearbox. Unfortunately, the procedure was interrupted and ended with a failure. Since then, the car has not started at all—the '3 bars of death' warning persists permanently. The technician mentioned that his diagnostic machine is currently out of service and will be unavailable for several months. I’ve already inspected the wiring harness visually and have replaced both the gearbox actuator and the gear position sensor with known-good units. Despite these efforts, the issue remains: the car still won as it cannot start. My personal OBD2 scanner has detected code P0702—'Transmission Control System Electrical Problem'. I'm confused about how a partial gearbox sync procedure could have permanently corrupted the transmission control module (TCM), especially since previously, simply disconnecting the battery would reset the system. The car has been inoperable for three months, but with renewed motivation at the start of the new year, I’m determined to get it back running. Any suggestions or troubleshooting steps would be greatly appreciated. As a last resort, could I bypass the transmission control system and directly connect the battery to the starter motor to initiate engine operation? Would this allow the gearbox to 're-sync' itself once running—without causing significant damage? Thank you in advance for your help. Paul.