P0766: Shift Solenoid D Performance or Stuck Off
What to do
You may notice the gearbox skipping a ratio or a gear change that feels larger than it should, rather than anything obviously broken. That is still worth investigating — on these transmissions the early symptom is usually mild.
What this code means
Solenoid D is electrically healthy but not moving when commanded. On a transmission with many ratios the practical effect is often subtler than a missing gear — the gearbox skips a ratio and shifts around the gap, so the complaint is a change that feels wrong or a rev drop that is too large, rather than an obvious failure.
That subtlety is worth naming, because a fault which produces only an odd-feeling shift is easy to dismiss until it develops into something less ambiguous.
Likely causes
Start here
- Debris in the transmission fluid · moderate
- Failed shift solenoid · moderate
- Low or degraded transmission fluid · easy
Less common
- Stuck valve in the valve body · specialist
- Low transmission line pressure · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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