Shift Solenoid "B" Control Circuit High
The P0977 code indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected a high voltage condition in the control circuit for shift solenoid 'B'. This typically means the circuit is shorted to voltage or has an open circuit, causing the feedback voltage to remain higher than the expected operational threshold.
Transmission shift solenoid issues can cause unpredictable shifting, gear engagement failure, or force the vehicle into limp mode. It should be addressed immediately to prevent internal transmission damage and ensure safe drivability.
Common symptoms
- Illuminated Check Engine Light
- Harsh, delayed, or erratic transmission shifting
- Transmission stuck in a specific gear (limp mode)
- Decreased fuel efficiency
- Inability to shift into certain gears
Likely causes
- Faulty shift solenoid 'B'
- Short to voltage or open circuit in the shift solenoid 'B' wiring harness
- Corroded, damaged, or loose electrical connectors in the transmission circuit
- Dirty or contaminated transmission fluid causing solenoid malfunction
- Low transmission fluid level
- Faulty Transmission Control Module (TCM) or PCM
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Low fluid levels or dark, burnt, and debris-filled fluid which can impede solenoid operation and damage internal components.
Inspect the wiring harness and connectors for shift solenoid 'B'.
Look for: Frayed wires, melted insulation, or corroded pins that could cause an open circuit or a short to voltage.
Measure the resistance of shift solenoid 'B' using a digital multimeter.
Look for: Resistance readings outside the manufacturer's specified range, indicating an internally failed solenoid that requires replacement.
Check for voltage at the shift solenoid 'B' connector while the circuit is active.
Look for: Continuous high voltage when the PCM/TCM is commanding the solenoid off, indicating a short to power in the wiring harness.
Command the solenoid on and off using a bi-directional scan tool.
Look for: Lack of an audible click from the transmission pan or failure of the scan tool to show state changes, confirming a circuit or solenoid failure.
This page explains the generic P0977 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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