Faulty shift timing solenoid B (internal coil failure or sticking valve); Contaminated or degraded transmission fluid causing solenoid malfunction; Wiring harness damage or poor electrical connection at the solenoid; Valve body wear or sticking shift valves affecting solenoid performance; Transmission control module software calibration issue or internal fault; Low transmission fluid level due to a leak

DTC codes / P07xx · Transmission / P078B

P078BShift Timing Solenoid B Range/Performance

Q: What does code P078B mean?

Shift Timing Solenoid B Range/Performance. P078B indicates that the transmission control module has detected an out-of-range or performance issue with shift timing solenoid B, which controls hydraulic pressure during gear changes. The computer compares expected shift timing against actual response and flags the solenoid circuit or mechanical function as faulty.

P078B indicates that the transmission control module has detected an out-of-range or performance issue with shift timing solenoid B, which controls hydraulic pressure during gear changes. The computer compares expected shift timing against actual response and flags the solenoid circuit or mechanical function as faulty.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Harsh or delayed shifts, especially when changing between specific gears
Transmission may slip or flare during acceleration
Check engine light or transmission warning light illuminated
Limp mode engagement with reduced power and limited gear selection
Often no symptoms besides the warning light, especially in early stages

Common causes, most likely first

Faulty shift timing solenoid B (internal coil failure or sticking valve)
Contaminated or degraded transmission fluid causing solenoid malfunction
Wiring harness damage or poor electrical connection at the solenoid
Valve body wear or sticking shift valves affecting solenoid performance
Transmission control module software calibration issue or internal fault
Low transmission fluid level due to a leak

How to diagnose and fix it

Check transmission fluid level and condition; top off or replace if contaminated
Inspect solenoid B wiring and connector for corrosion, chafing, or loose pins
Perform a resistance and voltage drop test on solenoid B circuit
Use a scan tool to command solenoid B and observe shift timing response
Replace shift timing solenoid B if electrical tests fail or valve is stuck
Inspect valve body for wear or debris; clean or replace as needed
Clear codes and perform a relearn or adaptation drive cycle to verify repair

Solenoid B faults often misdiagnosed

A sticking valve body spool can mimic a failed solenoid B, so replacing the solenoid alone may not fix the code.
Debris from a failing torque converter or worn clutches can clog solenoid screens and cause performance codes without total solenoid failure.
Some vehicles require a transmission control module relearn after solenoid replacement; skipping this step can leave the code pending.
Intermittent wiring faults from heat or vibration may only set the code under specific driving conditions, so wiggle tests are essential.
Low fluid level from a slow leak often triggers solenoid performance codes before any visible leak is noticed.

Can I keep driving with P078B?

You can usually drive cautiously to a repair shop, but avoid heavy acceleration, towing, or long trips because shift timing faults can worsen and lead to transmission damage. If the vehicle enters limp mode or shifts become severely harsh, stop driving and seek professional service.

Tools that help

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