The P0766 code indicates that the engine control module has detected a performance problem with shift solenoid D, specifically that it is stuck in the 'off' position. This means the solenoid is not allowing fluid to flow through the circuit as commanded, preventing the transmission from completing a specific gear shift.
The solenoid has suffered internal mechanical failure or an electrical short, preventing it from opening.
Insufficient fluid levels or debris in the fluid can block the solenoid orifice or prevent it from actuating.
Worn seals or a cracked valve body can cause fluid to bypass the solenoid, simulating a 'stuck off' condition.
Frayed, corroded, or broken wires leading to the solenoid can interrupt the signal from the control module.
A malfunction in the PCM or TCM may result in an incorrect signal being sent to the solenoid.
If the fluid was severely low or contaminated, a fluid change might resolve the issue, but it will not fix a mechanically failed solenoid.
No, it is very uncommon. This code is almost always caused by the solenoid itself, wiring issues, or hydraulic failures within the transmission.
The vehicle may still be drivable, but shifting will be abnormal and continued operation may cause further wear to the internal clutches.