TB25 - Transmission Control Indicator Light Never On

- Verify over drive is functional.

- Run Key On Engine Running (KOER) Self-Test. Key ON Engine Running (KOER) Self-Test

- Is Diagnostic Trouble Code (DTC) 631 present?

Yes -- Go to TB3. TB3 - Diagnostic Trouble Codes 97, 623 and 631

No -- Go to TB26. TB26 - Check For Voltage at Fuse Panel