P0783: 3-4 Shift Malfunction
What to do
If the fault is around the change into top gear, ask whether it persists with torque converter lock-up disabled. That check distinguishes a shift problem from a converter problem without taking anything apart, and the two are repaired very differently.
What this code means
The change from third to fourth did not complete correctly. On many four-speed automatics fourth is overdrive, applied by its own dedicated clutch — and it is frequently also where torque converter lock-up first engages.
That overlap causes a specific confusion worth heading off. A lock-up clutch applying at the same moment as the 3-4 change makes a converter problem and a shift problem feel identical from the driver's seat. Commanding lock-up off with a scan tool and repeating the change separates them in a couple of minutes, and it should happen before anything is dismantled.
Likely causes
Start here
- Low or degraded transmission fluid · easy
- Slipping torque converter clutch · specialist
- Failed shift solenoid · moderate
Less common
- Stuck valve in the 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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