P0778🔧 Transmission / Hydraulic pressure controlStop and fix promptly

P0778: Pressure Control Solenoid B Electrical (Meaning, Causes, Fixes)

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0778 means

An automatic transmission changes gears by applying clutches and bands with fluid pressure. The control module uses pressure control solenoids to set that pressure in each hydraulic circuit at the right moment. OBD-Codes.com says the powertrain control module (PCM) sets P0778 when pressure control solenoid B is experiencing an electrical malfunction. RepairPal defines P0778 as Pressure Control Solenoid "B" Electrical, but its explanation only says the transmission control module (TCM) sets it when a pressure control solenoid is not performing as desired. P0778 belongs to the B solenoid family: P0775 (general malfunction), P0776 (performance or stuck off), P0777 (stuck on), P0778 (electrical) and P0779 (intermittent) (OBD-Codes.com, RepairPal). It is a generic OBD-II code that OBD-Codes.com says shows up on Ford, Lincoln, Mercury, Jaguar, Chevrolet, Toyota, Nissan, Allison/Duramax, Dodge, Jeep, Honda, Acura and other vehicles, but the exact test values and repair steps vary by transmission, so the vehicle's service information should come first.

Severity: can I keep driving?

Stop and fix promptly

Get it checked soon. RepairPal rates P0778 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com calls it moderate at first but says it can get worse quickly if it isn't fixed. The transmission may slip, overheat, catch in gear or drop into limp mode, so avoid hard acceleration, towing and long trips until it's diagnosed, and get off the road safely if it suddenly loses drive.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Corroded or damaged connector, or faulty or damaged wiring (both sources)
  2. Failed pressure control solenoid (both sources)
  3. Low transmission fluid (RepairPal), or dirty or contaminated fluid (OBD-Codes.com)
  4. Dirty or clogged transmission filter (OBD-Codes.com)
  5. Faulty transmission control module (RepairPal) or PCM (OBD-Codes.com)
  6. Defective transmission pump, defective valve body or restricted hydraulic passages (OBD-Codes.com)
  7. The sources differ: RepairPal lists only the module, low fluid, the solenoid and wiring, while OBD-Codes.com adds fluid contamination, the filter, the pump, the valve body and blocked passages. They also disagree on severity, with RepairPal rating it Urgent and OBD-Codes.com calling it moderate at first, and they name different computers (TCM versus PCM) as the one that sets the code. Neither source explains why fluid or hydraulic faults would set an electrical code, so with P0778 the wiring, connector and solenoid circuit are the logical place to start

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes and freeze frame data before clearing anything; other B solenoid codes (P0775 to P0779) or other transmission codes can point to the real cause.
  2. Check for technical service bulletins (TSBs) for your vehicle, year and transmission; OBD-Codes.com says this can save a lot of time.
  3. Inspect the wiring and connectors to the transmission pressure control solenoids, the pump (if electric) and the computer for damage, corrosion, loose connections or damaged pins.
  4. Check the transmission fluid level and condition using the procedure in your owner's or service manual, and look for burnt smell, dark color or debris.
  5. Check your records for when the fluid and filter were last changed (OBD-Codes.com).
  6. Further testing needs a digital multimeter and your vehicle's specific voltage and resistance specs; OBD-Codes.com says wiring should normally read 0 ohms with the power off unless the service data says otherwise, and that resistance or no continuity means an open or shorted wire to repair.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The transmission is slipping, overheating or stuck in limp mode
  • The wiring and connectors look fine and the code comes back
  • Testing needs the solenoid circuit specs, a scan tool or removing the pan and valve body
  • The fluid is burnt or full of debris
  • OBD-Codes.com warns this code can be misdiagnosed as an engine misfire, a transmission pump problem, an internal transmission problem or a driveline problem, so a proper diagnosis matters before buying parts

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0778 serious?

Treat it as serious. RepairPal rates it Urgent. OBD-Codes.com says it usually starts as moderate but can get worse quickly, with slipping, overheating, catching in gear and limp mode possible.

What's the difference between P0777 and P0778?

Both point at pressure control solenoid B. P0777 means it is stuck on, while P0778 means there is an electrical malfunction in the solenoid or its circuit (OBD-Codes.com, RepairPal).

Can bad wiring cause P0778?

Yes. Both sources list wiring problems, and OBD-Codes.com also lists corroded or damaged connectors, so inspecting the solenoid wiring and connector is a sensible first step.

How much does it cost to fix P0778?

Neither source gives a repair cost. It can range from a connector or wiring repair to a new solenoid, valve body or control module, so get a diagnosis and a written estimate first.

Sources

  1. OBD-Codes.com: P0778 Pressure Control Solenoid B Electrical (John Ingalls)
  2. RepairPal: P0778 Pressure Control Solenoid "B" Electrical (rated Urgent)

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.