What it means
The control module detects a high electrical level in the shift solenoid B control circuit.
At a glance
- Usually lights the check-engine light
How it works
Shift solenoid B is an electrically controlled valve that directs fluid for transmission gear changes. The control module monitors the B control circuit and sets P0977 when its electrical level is higher than expected. A short to battery power, including a pinched supply wire touching a B+ source, can hold the circuit high.
Common causes
Most likely first.
- Short to battery
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Save freeze-frame data and examine live transmission data to establish when the solenoid B circuit went high.
- Inspect the B circuit harness for a pinched supply wire or damaged insulation touching a battery-positive source.
- Check the solenoid B connector for corrosion, loose or spread pins, and signs of incorrect contact.
- Use the wiring diagram to test the B control circuit for a short to battery voltage and locate any damaged section.
- Test solenoid B and its circuit against the manufacturer’s specification before replacing parts.
- Check the transmission control module only after confirming the circuit is not shorted and solenoid B passes its tests.
Common fixes
- Repair wiring that is pinched or shorted to a battery-positive source in the solenoid B circuit.
- Repair corroded, loose, or damaged solenoid B connector terminals.
- Replace shift solenoid B if it fails the specified test.
- Repair or replace the transmission control module if testing verifies an internal fault.
Can I keep driving?
If the transmission shifts harshly, slips, or delays engagement, avoid high loads and long trips, and stop if drive becomes unreliable. A B circuit held high can interfere with shifts, and continued abnormal operation can worsen transmission wear.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.