EngineLightCodes
Powertrain code

P0778 Pressure Control Solenoid B Electrical

Severity
Fix soon
Typical repair cost
$160–$2,750
Do it yourself
Shop job
Shop time
1–6 hours

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.

How the engine computer detects it

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.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

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

Common causes

  1. Harness or connector shorted or open Most likely
  2. Pressure valve B coil faulty – often only replaceable with the valve body Most likely
  3. Transmission module faulty Possible
  4. System voltage Less likely

How to diagnose P0778

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: pressure control solenoid, transmission valve body, transmission clutches, transmission control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
7
Transmission
78
Specific fault

Questions drivers ask

Can I drive with code P0778?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0778?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.