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 the specific solenoid identified by the manufacturer). This solenoid is responsible for directing transmission fluid to engage specific gears. A high voltage reading typically points to a short to power, a faulty solenoid, or an internal PCM issue. This can cause erratic shifting, transmission slippage, or limp mode.
01. Most Common Causes
- Short to power in the solenoid control circuit
- Faulty shift solenoid
- Damaged wiring or connector
- Internal PCM failure
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission stuck in gear or limp mode
- Decreased fuel economy
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all codes and freeze frame data.
Step 2: Inspect the transmission wiring and connectors for damage, corrosion, or shorts.
Step 3: Test the shift solenoid resistance with a multimeter (typically 20-30 ohms).
Step 4: Check for voltage at the solenoid connector with the key on; compare to manufacturer specs.
Step 5: If wiring and solenoid are good, suspect a PCM fault and perform further diagnostics.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a high voltage solenoid circuit can cause transmission damage or unsafe driving conditions due to erratic shifting.
How much does it cost to fix?▼
Repair costs range from $150 to $400, depending on the cause. A solenoid replacement is typically $150-$300, while PCM replacement can exceed $800.