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. P0778 is the electrical code for valve B. Allison compares current with the duty cycle after 125 ms, after one trip; Mitsubishi's 2009 CVT flags at most 400 mA with 750 mA commanded for 5 s; the 2022 Jatco CVT uses P0778 only for a short to ground; Saab's AF40 flags a deviation between commanded and feedback current of valve SLC1 and keeps only second gear and reverse. Harsh engagement, weak acceleration and no lock-up 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 engagement jolt
- Weak pulling away and acceleration
- Limp mode (Saab: second and reverse only)
- Check engine light
Most likely causes
- Harness or connector shorted or open
- Pressure valve B coil faulty – often only replaceable with the valve body
- Transmission module faulty
- System voltage
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It can trigger limp mode.
- It affects emissions.
What each character of P0778 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 7: Transmission
- 78: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0778?
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 P0778?
The most common causes are: harness or connector shorted or open; pressure valve B coil faulty – often only replaceable with the valve body; transmission module faulty.
Related codes
- P0776Pressure Control Solenoid B Performance/Stuck Off
- P0779Pressure Control Solenoid B Intermittent
- P0965Pressure Control Solenoid B Control Circuit Range/Performance
- P0966Pressure Control Solenoid B Control Circuit Low
- P0967Pressure Control Solenoid B Control Circuit High
- P0798Pressure Control Solenoid C Electrical
Sources
- saabwisonline.com: dtc p0778 or p0965 p0967
- mitsubishitechinfo.com: M123120660016900USA
- mitsubishitechinfo.com: N5040201C0009600USA
- gsi.ext.gm.com: 2006trans9
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.