Possible reasons for the lack of power from the automatic transmission control unit:
Wiring:
* Damaged or loose wires going to the automatic transmission control unit.
* Poor connections or corrosion in connectors.
* Break or short circuit in the automatic transmission wiring harness.
Fuses and relays:
* A blown fuse or faulty relay that supplies power to the control unit.
* Loose or oxidized contacts in the fuse or relay socket.
Faulty power supply:
* Internal failure of the electronic transmission control module (TCM) or control module (PCM), which regulates power to the automatic transmission control unit.
* Failure of the power source inside the automatic transmission control unit.
Ground connection:
* Poor ground connection of the automatic transmission control unit or other automatic transmission-related components.
*Corrosion or damage to the ground cable.
Other possible reasons:
* Failure of the gear shift position sensor.
* Gear shift lever malfunction.
* Damage to the automatic transmission control unit as a result of transmission fluid leakage or external influence.
Diagnostics and troubleshooting:
1. Check Wiring: Inspect wires, connectors, and wiring harnesses for damage or loose connections.
2. Check fuses and relays: Check the relevant fuses and relays using a tester or replace them with new ones.
3. Check the automatic transmission control unit: Use a diagnostic scanner to check for trouble codes indicating a faulty control unit.
4. Check the ground connection: Make sure the automatic transmission control unit and other components have a proper ground connection.
5. Check the shift position sensor and shift lever: Make sure the sensor and shift lever are working properly.
6. Replace the automatic transmission control module: If other diagnostic steps do not reveal problems, the automatic transmission control module may need to be replaced.
Note: Before performing any diagnostics or repairs, be sure to disconnect the negative battery terminal to prevent damage to electronic components.