P0977: Shift Solenoid B Control Circuit High
Severity: medium
What it means: The engine or transmission computer saw that the electrical circuit for automatic transmission shift solenoid B reads as open (no current path) when the solenoid is supposed to be off.
Safe to drive? Short trips only, with care. The computer usually works around the bad solenoid, so some gears may be missing or shifts may be harsh. Get it checked soon.
Common symptoms
- Check-engine light
- Harsh or missing shifts, or the transmission stuck in one gear (limp mode)
- Poorer acceleration or fuel economy
Likely causes, ranked
- Broken or chafed wire, or a loose or corroded connector, in the solenoid B circuitShop
- Failed shift solenoid B coilShop
- Low or old transmission fluid (worth checking with any shift code)Shop
- Engine or transmission computer fault (less common)Shop
Vehicle-specific notes
- :
DIY or shop?
Mostly shop. Checking the connector and fluid is DIY-friendly. Testing solenoid resistance and the wiring needs a meter and a service manual. Toyota's manual, for example, flags an open circuit when the solenoid reads 100,000 ohms or more, and lists a normal coil at about 11 to 15 ohms on that transmission. Specs vary by car.
Vehicle notes
- 2009 MINI Clubman (non-turbo): an owner had P0977 at 95,000 miles. Car Talk members listed the solenoid, its harness and connectors, and a transmission service.
Before you replace parts
- Read all stored codes. A matching "low" code (P0976) or other solenoid codes change the diagnosis.
- Check the transmission connector and wiring for damage or corrosion.
- Check your VIN for recalls, service bulletins and extended coverage.
- Clear the code only after a repair, then confirm it stays off.
Safety / mechanic note
Verify with a mechanic. A transmission that drops gears or gets stuck can be unsafe in traffic. A code points to a circuit, not always a specific part.