P078B: Shift Timing Solenoid B Range/Performance

What it means

Shift timing solenoid B is electrically intact, but actual shift timing does not match the model — same failure modes as solenoid A (aged, dirty ATF), applied to the second timing channel.

At a glance

• Usually lights the check-engine light

How it works

Shift timing solenoid B controls a second transmission shift-timing channel. This range/performance code means the TCM sees an electrical signal but the resulting solenoid response or shift timing does not match its expected model, rather than simply detecting a circuit open or short.

Common causes

Most likely first.

1. Aged solenoid with weakened force
2. Sensor element aged beyond calibration window
3. Sensor mounting loose - signal damping

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Save the freeze-frame data and compare commanded solenoid B operation with transmission live data to identify the gears and conditions where timing falls outside expectations.
2. Check the transmission fluid level and condition using the manufacturer's specified procedure, since degraded fluid can affect solenoid response.
3. Inspect solenoid B and its connector for secure mounting, corrosion, fluid intrusion, and damaged wiring.
4. Check solenoid B circuit integrity and coil operation against the manufacturer's specification.
5. If those checks pass, evaluate solenoid B response and the related hydraulic shift operation using manufacturer procedures.

Common fixes

• Correct low or degraded transmission fluid using the specified fluid and service procedure.
• Repair a loose, corroded, or damaged solenoid B connector or wiring.
• Secure a loose solenoid B mounting if confirmed.
• Replace shift timing solenoid B if its response is outside specification.
• Address a confirmed hydraulic restriction affecting the solenoid B shift channel.

Can I keep driving?

If shifts remain smooth, drive gently and avoid towing or strenuous use until diagnosed. Slipping, shuddering, or delayed shifts can generate heat and accelerate transmission wear; stop if the symptoms become severe.