Faulty shift timing solenoid B, often due to internal coil degradation or sticking; Damaged or corroded wiring harness or connector at the solenoid or TCM; Low or contaminated transmission fluid causing erratic solenoid operation; Valve body wear or debris blocking the solenoid's hydraulic circuit; Poor electrical ground or intermittent open in the solenoid control circuit; TCM software glitch or internal fault misreporting the solenoid signal

DTC codes / P07xx · Transmission / P078E

P078EShift Timing Solenoid B Intermittent

Q: What does code P078E mean?

Shift Timing Solenoid B Intermittent. P078E indicates that the transmission control module (TCM) has detected an intermittent fault in the circuit or operation of shift timing solenoid B, which is responsible for precisely controlling hydraulic pressure during gear changes. The TCM monitors the solenoid's electrical current and response time, and when the signal deviates from expected values even briefly, it sets this code and may command a fail-safe mode.

P078E indicates that the transmission control module (TCM) has detected an intermittent fault in the circuit or operation of shift timing solenoid B, which is responsible for precisely controlling hydraulic pressure during gear changes. The TCM monitors the solenoid's electrical current and response time, and when the signal deviates from expected values even briefly, it sets this code and may command a fail-safe mode.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
Harsh or delayed gear shifts, particularly when the transmission is cold or under light throttle
Intermittent slipping or flaring during upshifts or downshifts
The transmission may enter limp mode, sticking in a single gear until the ignition is cycled
Occasional shudder or hesitation when accelerating from a stop

Common causes, most likely first

Faulty shift timing solenoid B, often due to internal coil degradation or sticking
Damaged or corroded wiring harness or connector at the solenoid or TCM
Low or contaminated transmission fluid causing erratic solenoid operation
Valve body wear or debris blocking the solenoid's hydraulic circuit
Poor electrical ground or intermittent open in the solenoid control circuit
TCM software glitch or internal fault misreporting the solenoid signal

How to diagnose and fix it

Check transmission fluid level and condition; top off or replace fluid if contaminated
Inspect the solenoid B electrical connector and wiring for corrosion, chafing, or loose pins
Measure the solenoid's resistance and compare to the manufacturer's specification
Perform a voltage drop test on the solenoid control circuit while wiggling the harness to catch intermittent faults
Use a scan tool to command the solenoid on and off and observe its response and current draw
Remove and bench-test the solenoid, or replace it if resistance is out of range or it fails activation
If the solenoid tests good, inspect the valve body for wear or debris and verify TCM software is up to date

Intermittent Solenoid Faults Often Misdiagnosed

A solenoid that tests fine when cold can still fail intermittently when hot, so always test the circuit both cold and at operating temperature.
Debris in the transmission fluid can temporarily jam the solenoid, causing the code to set only under specific driving conditions; a fluid flush may resolve it without parts replacement.
The TCM may set P078E due to a momentary voltage spike or ground fault elsewhere in the vehicle, so check for other electrical codes before condemning the solenoid.
Some transmissions use shift timing solenoids that are not serviceable separately from the valve body, making diagnosis of the entire assembly critical before replacement.
A failing transmission filter can starve the solenoid of fluid, mimicking an electrical fault; always verify fluid pressure and filter condition.

Can I keep driving with P078E?

You can usually drive the vehicle short distances to a repair shop, but avoid aggressive acceleration or heavy towing because intermittent solenoid failure can cause harsh shifts or sudden limp mode. If the transmission slips severely or refuses to engage gears, stop driving and seek professional service.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.