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P0766 is a diagnostic trouble code (DTC) for "Shift Solenoid D Performance or Stuck Off". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0766 code indicates that there has been an abnormal voltage reading detected by the PCM in the shift solenoid D.
Shift solenoids are used to managed the hydraulic fluid transfer between circuits, and to assist in the process that allows a vehicle to decelerate and accelerate. These solenoids must be able to actuate varying gear ratios to achieve vehicle speed and engine performance. If a solenoid (in this case, shift solenoid D) is not performing correctly, or is stuck in the off position, the engine will not perform at optimal level. In this case, the PCM will store the P0766 code.
The most likely causes include:
In many cases, there are no symptoms at all beyond the illumination of the Check Engine lamp. However, some vehicle owners may observe:
After verifying the code with an OBD-II scanner, the mechanic should begin by inspecting the transmission fluid. If the fluid is too low, dirty, or smells burnt, it needs to be refilled or replaced with clean fluid. In the event that the transmission fluid is heavily contaminated, the entire system may need to be flushed and refilled.
The next step is to inspect all electrical components, and replace or repair any that are damaged, loose, corroded, or otherwise inoperable. After this step, a mechanic should check the hydraulic pressure, the shift solenoid function, and all related circuits until the improperly functioning component is found.
After every attempted repair is complete, the P0766 code should be cleared from the system, and a retest should be performed. If the code does not reappear, the mechanic has successfully diagnosed the issue, and will know precisely which component was causing the issue.
The most common mistake made when diagnosing the P0766 code is jumping right to the shift solenoid itself, and replacing that component, rather than first checking the circuit components for electrical issues.
If the P0766 code is being detected, it indicates an issue that directly affects the operation of the vehicle. Even when symptoms are not present, this code means that the vehicle may not be operation for much longer, or that more expensive repairs will be needed down the road. If the P0766 code is detected, it should be dealt with immediately.
There are many ways that a technician can address a P0766 code detection. They include:
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