P0784: 4-5 Shift Malfunction
What to do
You may not feel anything at all, or only a slight hesitation at motorway speeds. If a garage says it drove fine, ask whether the test drive included enough sustained speed to reach top gear — this change does not happen in town.
What this code means
The change from fourth to fifth did not complete correctly. As a high-gear shift it happens at low torque and usually at steady speeds, so it is both the gentlest change the transmission makes and the least likely to be noticed going wrong.
That has a practical consequence: a fault here often shows up as a code before it shows up as a complaint, and it will not reproduce on a short test drive around town. A workshop reporting that the vehicle drove perfectly may simply not have reached the conditions in which this change happens.
Likely causes
Start here
- Low or degraded transmission fluid · easy
- Low transmission line pressure · specialist
- Failed shift solenoid · moderate
Less common
- Worn valve body · specialist
- Worn clutch packs · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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