P0777

P0777 means Pressure Control Solenoid B is stuck on, i.e., the PCM has determined the solenoid is delivering maximum pressure regardless of duty-cycle command, or that commanded pressure changes produce no hydraulic response in the stuck-high direction. Cheapest-first: connect a scan tool, command EPC duty-cycle changes (or current changes on current-controlled systems), and watch line pressure on a mechanical gauge at the test port. If line pressure stays pegged at the high end (for example, 240 to 280 psi on 4L60E full-throttle pressure regardless of command), the solenoid plunger is mechanically stuck or the regulator valve is jammed. Measure solenoid resistance to confirm it is not electrically shorted (spec typically 3 to 7 ohms for GM force motors, 4 to 6 ohms for Toyota/Ford PC solenoids). Drop the pan and inspect for contamination: P0777 is frequently caused by a single piece of clutch debris or a broken check ball wedged in the solenoid screen or bore. Inspect the pressure regulator and boost valves for sticking with a flashlight and pick. Caveat: a stuck-on PC solenoid produces extremely harsh shifts that can quickly damage clutches, so do not drive the vehicle hard while diagnosing; tow if shifts are jarring.

Vehicle-specific patterns: 2000 to 2006 Chevrolet Silverado with 4L60E sets P0777 from debris from a failing 3-4 clutch wedging in the EPC screen, with GM PIP3911 calling for solenoid and filter replacement plus pan flush. 2003 to 2008 Dodge Durango with 545RFE trips P0777 from line pressure solenoid contamination inside the solenoid pack, requiring full pack replacement per Chrysler TSB 21-010-08. 2004 to 2009 Toyota 4Runner with A750F sets the SLT stuck-on equivalent from internal varnish, typically after extended fluid intervals. 2005 to 2011 Nissan Frontier/Xterra with RE5R05A trips the equivalent code from the line-pressure solenoid contamination and stepped valve body wear. Estimated repair: $280 to $1,500.