P0778 means Pressure Control Solenoid B Electrical. The transmission computer has found an electrical fault in pressure control solenoid B’s circuit. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0778 means
Electronically controlled automatics are run by a transmission control module (TCM), a separate box or part of the engine computer. It reads speed sensors, the range sensor and fluid temperature to decide when to shift, and drives solenoids that apply clutches and the torque converter clutch. Many basic code readers only show the generic P0700; a scan tool that reads the transmission module shows the specific fault. Check fluid level and condition first, since low or burnt fluid causes many transmission codes.
P0778 symptoms
- Harsh or soft shifts
- Slipping
- Limp mode
- Check engine light
Common causes of P0778
- Open or shorted solenoid coil
- Damaged internal harness
- Connector corrosion
How to diagnose P0778
- Check transmission fluid level and condition first
- Measure solenoid resistance at the transmission connector
- Inspect the internal harness and connector
Can you drive with P0778?
Limit driving; pressure problems can quickly damage clutches.
P0778 tips
Internal harness connectors can loosen with heat cycles; check the connector at the case before replacing the solenoid. Measure resistance through the case connector first, then directly at the solenoid if the pan is off.
Will P0778 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0778 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0777 | Pressure Control Solenoid B Stuck On |
| P0745 | Pressure Control Solenoid A |
| P0748 | Pressure Control Solenoid A Electrical |
Guides that help
When it is more than a sensor
If the fault turns out to be internal (worn clutches, a failed converter or a damaged valve body), compare a rebuild with a replacement in transmission rebuild vs replacement and transmission replacement cost, identify your unit with what transmission do I have?, and browse our transmissions.
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