What causes a P0778 code?

P0778 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P0778 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0778 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

OBD-II

P0778

Pressure Control Solenoid B Electrical Malfunction

What it means

The Engine Control Module (ECM) or Transmission Control Module (TCM) has detected an electrical problem or open circuit in the 'B' pressure control solenoid circuit, which regulates transmission hydraulic line pressure.