P0977 Gearbox solenoid: signal or voltage too high ("B")

By: Diagno editorial team · Updated: 2026-10-15

P0977 means: Gearbox solenoid: signal or voltage too high ("B"). The automatic gearbox module has found a fault. Drive gently and have the car checked soon. The repair usually costs about €80–400 in Estonia. The most common cause: connector loose, damp or corroded. Other possible causes: wire shorted to power or ground broken, faulty solenoid or sensor.

What it means

The automatic gearbox module has found a fault. The gearbox may go into limp mode: it holds one gear and shifts harshly or not at all. The signal voltage is too high. Usually a wire is shorted to power, the ground is broken or the part itself has failed.

What you may notice

• Stuck in one gear (limp mode)
• Harsh or late gear changes
• Gearbox slipping
• Engine or gearbox light on

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire shorted to power or ground broken
3. 3Faulty solenoid or sensor
4. 4Engine computer fault (rare)

Repair difficulty: Hard

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Read the gearbox module's own codes too. If the gearbox slips, drive gently and don't tow a trailer. Best left to a workshop. It needs a diagnostic tool and experience.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the solenoid or sensor

Standard SAE description: Shift Solenoid "B" Control Circuit High