Shift Solenoid Control Circuit High
The P0977 code indicates that the Powertrain Control Module (PCM) has detected a high voltage condition in the control circuit of shift solenoid 'B' (or a specific solenoid depending on the vehicle). This solenoid is responsible for directing transmission fluid to engage specific gears. A high voltage reading suggests a short to power, open circuit, or faulty solenoid, which can lead to improper transmission operation.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in gear or fails to shift
- Harsh or delayed shifts
- Reduced fuel economy
2. Most Common Causes
- Short circuit in the shift solenoid 'B' control circuit to battery positive (B+) or another high-voltage circuit
- Shift solenoid 'B' internal failure or coil short circuit
- Corroded, damaged, or high-resistance solenoid connectors or terminals
- Open or intermittently high-resistance wiring in the control circuit causing elevated voltage readings
- Faulty transmission control module (TCM) or powertrain control module (PCM), though less common
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect wiring and connectors for damage, corrosion, or shorts.
Step 3: Test solenoid resistance with a multimeter (typically 15-25 ohms).
Step 4: Check for voltage at the solenoid connector with key on (should be battery voltage).
Step 5: If wiring and solenoid are OK, test PCM output or replace PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the transmission may not shift properly, potentially causing internal damage or unsafe driving conditions.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts and labor. Solenoid replacement is the most common fix.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.