P0766 Toyota
The P0766 trouble code on Toyota vehicles indicates an issue with Shift Solenoid D, specifically performance issues or the solenoid being stuck off. The shift solenoid controls the flow of transmission fluid, allowing for smooth gear shifts. When this solenoid malfunctions, it can disrupt the operation of the automatic transmission.
Causes of P0766:
- Low or dirty transmission fluid – If fluid levels are low or the fluid is contaminated, it can interfere with solenoid operation.
- Faulty Shift Solenoid D – Mechanical failure within the solenoid can cause it to stick.
- Wiring or electrical issues – Broken wires, poor connections, or short circuits in the solenoid circuit.
- Internal transmission problems – Blockages in transmission fluid passages or hydraulic issues.
- ECM/TCM issues (rare) – Faulty Engine Control Module or Transmission Control Module.
Symptoms:
- Transmission may fail to shift into certain gears.
- Harsh or delayed shifting.
- Transmission slipping.
- Overheating of the transmission.
- The Check Engine Light or Service Engine Soon light will be illuminated.
Repairs to Fix P0766:
- Check and replace the transmission fluid if it’s dirty or low.
- Test and replace the Shift Solenoid D if faulty.
- Inspect and repair any damaged wiring or connectors.
- Clear blocked fluid passages within the transmission.
- If internal damage to the transmission exists, a rebuild or replacement may be required.
Diagnosing the Code:
A mechanic will use an OBD-II scanner to confirm the code and inspect transmission fluid. Electrical connections to the solenoid will also be tested, followed by hydraulic pressure checks.
Prompt repair is recommended as driving with a malfunctioning solenoid can lead to severe transmission damage over time.