Bad sensor. Cannot say exaclty which one, but I would assume the throttle position sensor. Could possibly be the switch on the shifter needs replacing, or the overdirve relay needs to be replaced.
Below is a method you can "self diagnose"
To get codes out of the Transmission Control Module (TCM). The lamp in the Overdrive OFF switch is used to signal the various flash codes. To view flash codes, proceed as follows:
- Turn ignition key ON-OFF-ON-OFF-ON finally leaving the key in the ON position. Leave the Overdrive OFF Switch in the normal overdrive (ON) position.
- Immediately begin counting the number of flashes displayed by the Overdrive OFF Switch indicator lamp.
- Flash codes will correspond to Powertrain Control Module codes in duration and spacing.
- A code 55 identifies the end of flash code transmission.
And the possible codes are:
- 11 No Engine Speed Sensor Signal
- 12 No Output Shaft Sensor Signal
- 13 No Vehicle Speed Sensor Signal
- 14 Governor Pressure Sensor Signal
- 15 Throttle Position Signal
- 16 Transmission Temperature Sensor
- 17 Overdrive Off Switch Circuit
- 18 System Voltage Out of Limits
- 19 Standby Voltage Out of Limits
- 21 Governor Pressure Solenoid Circuit
- 22 3-4 Solenoid Circuit
- 23 Torque Converter Clutch Circuit
- 24 Overdrive Off Lamp Circuit
- 25 EEPROM Checksum Error
- 26 Governor Pressure Sensor Offset Drift
- 55 End of Message
If you still get no codes, then we have to explore a mechanical problem inside the transmission. Possibly the overdrive solenoid not venting or a lower valve body malfunction.
best of luck and let us know?