P0777: Pressure Control Solenoid B Stuck On

Pressure control solenoids are current-controlled proportional valves, and what B and C mean depends on the design: on GM's clutch-to-clutch automatics they are the pressure valves of clutches 2 and 3, on GM's CVT B is primary pulley pressure and C line pressure, on Jatco CVTs B is the secondary pressure valve, on Saab's AF40 B and C are clutch valves SLC1/SLC2. P0777 means the valve is electrically fine but pressure stays applied – the off-going clutch does not release. GM's 9-speed flags clutch 2 slip below 50 rpm for 0.8 s on loaded downshifts, the 8-speed uses a torque and inertia phase test, Allison 25 rpm or less – all after one trip. GM's Honda-built five-speed cannot always separate it from P0746 and stores both. Harsh shift jolts, tie-up and a default gear follow.

Medium severity. Can I keep driving?Drive as little as possible and gently. If the transmission slips or stays in one gear, go slowly to a repair shop or call for a tow truck.

Symptoms

Harsh shift jolt, transmission ties up
Limp mode in a fixed gear
Check engine light

Most likely causes

Spool or pressure valve sticking
Clutch stuck or piston hanging
Contaminated fluid (debris after clutch damage)
Software or false setting

What to check, in order

Start with the simplest. You can tick off each step.

Check the fluid level and condition according to the manufacturer
Use the scanner to command the movement and compare the actual position with the requested one.
Check the transmission connector
Read the data with a transmission-compatible scanner
Measure the solenoid valve circuit
Leave opening the transmission to a specialized repair shop

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P0777 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
7: Transmission
77: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0777?

Drive as little as possible and gently. If the transmission slips or stays in one gear, go slowly to a repair shop or call for a tow truck.

What causes code P0777?

The most common causes are: spool or pressure valve sticking; clutch stuck or piston hanging; contaminated fluid (debris after clutch damage).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.