P0778 Fault Code

Long Description

Fault code P0778 is logged when the powertrain control module (PCM) has detected an electrical issue with the pressure control solenoid B in an automatic transmission.

Of course, the code can only be logged in vehicles that have an automatic transmission.

The shift control solenoids are fluid-operated controllers that are responsible for changing into the specified transmission layout based on the driving scenario.

This code indicates that there is likely an electrical fault causing a problem in the control solenoid B circuit.

In terms of the most common manufacturers for this code, Mercedes-Benz, Nissan, Toyota, and Subaru are near the top of the list. Again, only these models with automatic transmissions can suffer the code.

Other Signs of This Problem

There will typically be a number of significant symptoms when it comes to this fault code. These will all stem from the transmission not functioning properly.

The most obvious sign will be the presence of the Check Engine light on the dashboard.

Gear changes will also typically be affected. This can range in severity based on a number of conditions.

The most common issue will be harsh, erratic gear shifts. It is also possible that the vehicle will be unable to change gears at all.

An overheating transmission is also a fairly common symptom. This can occur if the problem leads to blocked fluid passages or is caused by issues with the transmission fluid.

Be sure to look out for additional transmission fault codes like P0745, P0755, and P0759 that can help pinpoint the cause of the issue.

What Could Be The Problem?

There are some fairly typical culprits when it comes to issues affecting tan automatic transmission. These can be both mechanical or electrical in nature, but the code suggests that it is electrical in nature.

Because the code points to an electrical issue, it is possible that the control solenoid itself is faulty. Similarly, there may be electrical faults in the control solenoid circuit like damaged wires or loose connections.

While not technically electrical, there are some simple issues that could lead to this code being logged.

Low, contaminated, or old transmission fluid can be one of the most common causes when it comes to any automatic transmission issue.

In addition to this, blockages in the transmission fluid passages can lead to this fault code. This is particularly true of a transmission that has any of the issues listed above.

Fixes

Because the code indicates that the cause of the issue is electrical, the first steps should be to inspect the control solenoid and its circuit.

A faulty control solenoid should be replaced. Similarly, if there are any electrical faults like those mentioned earlier, they need to be fixed accordingly.

Transmission fluid should be checked. If it is dirty, old, or otherwise contaminated, it needs to be replaced.

If the transmission fluid shows signs of dirt in any way, it may be necessary to clean the transmission fluid passages

Seriousness

Fault code P0778 is a fairly serious problem. It can lead to a number of significant driveability issues with an automatic transmission, particularly over time.

It is strongly recommended to have this fault code fixed immediately as to avoid more severe issues later on, which will likely also require more costly repairs. It may also cause the transmission to be inoperable, which is a serious issue.