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Error Code P0778 is defined as Pressure Control Solenoid B Electrical. This is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made since 1996 up to present and equipped with automatic transmission. This includes vehicles from, but not limited to, Acura, Allision / Duramax, Chevrolet, Dodge, Ford, Jaguar, Jeep, Lincoln, Mercury, Nissan, Toyota, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model and powertrain configuration.
Error Code P0778 is set when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a problem with the Transmission Pressure Control Solenoid “B”. Most automatic transmissions use at least three solenoids A, B, and C. The Trouble Codes related to Solenoid B also include:
These codes can be set based on the specific malfunctions that alert the PCM and activate the Check Engine light.
The job of the Transmission Pressure Control Solenoid is to control the fluid pressure to ensure the automatic transmission works properly. The PCM gets the electronic signal based on the pressure in the solenoids. An automatic transmission is controlled by a series of bands and clutches that changes the gears through fluid pressure sent at the right place and at the right time. Based on the signals sent from related devices that monitor the speed of the vehicle, the PCM controls the pressure solenoids to direct fluid at the right pressure to different hydraulic circuits which changes the transmission gear ratio at the right time.
Error Code P0778 is set when the PCM determines that the Pressure Control Solenoid “B” is experiencing an electrical problem.
- Vehicle in limp mode
- Overheated transmission
- Transmission slipping when shifting
- Transmission catches in gear
- Increase in fuel consumption
- Misfire like symptoms
- Not enough fluid level
- Clogged or dirty transmission filter
- Contaminated or dirty fluid
- Restricted passages in the hydraulic
- Defective transmission valve
- Defective shift solenoid
- Internal failure in transmission
- Corroded or damaged connector
- Damaged or faulty wiring
- Defective PCM
How to Check
Before starting with any troubleshooting process, it’s important to check the with vehicle’s TSB (Technical Service Bulletins), specific to its year, model, and transmission. In some cases, this can help save a lot of time, as it points you in the right direction. Also, it pays to check the vehicle’s records to verify the last time the fluid and filter was changed.
Inspect Fluid and Wiring
First, check the transmission fluid’s condition and level. Before this, you can consult with the vehicle’s records to verify the last time the fluid and filter was changed.
For the wirings, it’s obvious. Make sure the connectors and connections are secured, and there are no signs of damages and corrosions. This includes inspecting all wirings and connectors to the transmission pressure control solenoids, transmission pump, and PCM. Depending on the configuration, the transmission pump can be electrically or mechanically driven.
These steps may vary from one vehicle to another, and requires advanced equipment to perform, such as digital multi-meter and specific technical references for the vehicle. You will need the specific troubleshooting guidelines for your vehicle prior to proceeding with this kind of diagnosis.
Also, remember that voltage conditions may vary based on the model of the vehicle. Fluid pressure requirements can also vary based on the design and configuration of the transmission.
Unless it was specified in the technical data, the normal resistance reading for connections and wirings is 0 ohms. Continuity check should be performed with the power removed from the circuit to avoid shorting the circuit and doing more damage. Resistance or no continuity is a sign of faulty wiring, which may be open or shorted, and must be repaired, if not replaced.
Often times, this code can be misdiagnosed as:
- Engine misfire problem
- Internal transmission problem
- Transmission pump problem
- Driveline problem
How to Fix
- Replacing fluid and filter
- Repair or replacement of defective transmission valve body
- Repair or replacement of defective shift solenoid
- Repair or replacement of defective transmission
- Cleaning passages through a transmission flush
- Cleaning connectors off of corrosions
- Repair or replacement of faulty wiring
- Replacement or flashing of PCM
The severity of this code starts at moderate, but it can develop into something serious when not corrected soon enough.