Powertrain, generic · Transmission

P0778 Pressure Control Solenoid B Electrical

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

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

Symptoms

  • Harsh engagement jolt
  • Weak pulling away and acceleration
  • Limp mode (Saab: second and reverse only)
  • Check engine light

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–2,500
Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

pressure control solenoidtransmission valve bodytransmission clutchestransmission control module

Related codes

P0776P0779P0965P0966P0967P0798

References: saabwisonline.com, mitsubishitechinfo.com, mitsubishitechinfo.com, gsi.ext.gm.com.