What Does It Mean?
This is a generic diagnostic trouble code (DTC) and generally applies to OBD-II equipped vehicles with an automatic transmission.
This may include, but is not limited to, vehicles from Ford, Mercury, Lincoln, Jaguar, Chevrolet, Toyota, Nissan, Allison/Duramax, Dodge, Jeep, Honda, Acura, etc. Although generic, the exact repair steps may vary by year, make, model, and powertrain configuration.
When the OBD-II trouble code P0778 is set, the Powertrain Control Module (PCM) has detected a problem with the transmission pressure control solenoid “B”. Most automatic transmissions have at least three solenoids which are solenoids A, B, and C. The trouble codes related to solenoid “B” are codes P0775, P0776, P0777, P0778, and P0779. The set of codes is based on the specific malfunction that alerts the PCM and illuminates the Check Engine light.
The purpose of the transmission pressure control solenoids is to control fluid pressure for the proper operation of an automatic transmission. The PCM receives an electronic signal based on the pressure inside the solenoids. An automatic transmission is controlled by bands and clutches that shift gears by having fluid pressure in the right place at the right time. Based on signals from associated devices monitoring vehicle speed, the PCM commands the pressure solenoids to direct fluid at the appropriate pressure to various hydraulic circuits that change the gear ratio at the right moment.
The P0778 code is set by the PCM when the pressure control solenoid “B” experiences an electrical malfunction.
How severe is this DTC?
The severity of this code normally starts as moderate, but it can escalate to a more severe level quickly when not corrected in a timely manner.
What are some of the symptoms of the code?
Symptoms of a P0778 trouble code may include:
Vehicle enters limp mode
Transmission slips when shifting gears
Transmission overheating
Transmission shifts harshly
Reduced fuel economy
Symptoms
Potential misfires
Check Engine light illuminated
What are some of the common causes of the code?
Causes
of this P0778 transmission code may include:
Faulty pressure control solenoid
Dirty or contaminated fluid
Dirty or clogged transmission filter
Faulty transmission pump
Faulty transmission valve body
Restricted hydraulic passages
Corroded or damaged connector
Faulty or damaged wiring
Faulty PCM
What are the troubleshooting steps for P0778?
Before starting the troubleshooting process for any malfunction, you should research Technical Service Bulletins (TSBs) for the specific vehicle by year, model, and transmission. In some circumstances, this can save you a lot of time in the long run by pointing you in the right direction. You should also check the vehicle records to verify the last time the filter and fluid were changed if possible.
Fluid and Wiring Inspections
The first step is to check the fluid level and examine the condition of the fluid for contamination. Before changing the fluid, you should check the vehicle records to verify the last time the filter and fluid were changed.
A detailed visual inspection to check the condition of the wiring for obvious defects is next. Check the connectors and connections for security, corrosion, and damaged pins. This should include all wiring and connectors for the transmission pressure control solenoids, transmission pump, and PCM. Depending on the configuration, the transmission pump may be electric or mechanical.
Advanced Steps
Advanced steps always become very vehicle-specific and require appropriate advanced equipment to perform accurately. These procedures require a digital multimeter and the vehicle-specific technical references. You must obtain the troubleshooting guidelines specific to your vehicle before proceeding with the advanced steps. Voltage requirements can be very specific to the vehicle model. Fluid pressure requirements will also vary depending on the transmission design and configuration.
Continuity Checks
Unless otherwise specified in the technical data, normal readings for wiring and connections should be 0 ohms of resistance. Continuity checks should always be performed with the power disconnected from the circuit to avoid shorting the circuit and causing more damage. Resistance or lack of continuity is an indication of faulty wiring that is open or shorted and must be repaired or replaced.
What are the common repairs for this code?
Replacing the fluid and filter
Replacing the faulty pressure control solenoid
Repairing or replacing a faulty transmission pump
Repairing or replacing the faulty transmission valve body
Flushing the transmission to clean the passages
Cleaning corroded connectors
Repairing or replacing wiring
Reprogramming or replacing the PCM
Possible misdiagnosis may include:
Engine misfire issue
Transmission pump problem
Internal transmission problem
Transmission issue
I hope the information in this article has helped point you in the right direction to fix the issue with your pressure control solenoid trouble code. This article is strictly informational, and the technical data and service bulletins specific to your vehicle should always take priority.