P0977
UniversalShift Solenoid B Control Circuit High
Medium SeverityThis code indicates that the Powertrain Control Module (PCM) has detected a higher than normal voltage in the control circuit for Shift Solenoid B. This electrical issue prevents the solenoid from functioning correctly, leading to problems with the transmission's ability to shift gears smoothly or at all.
⚠️ Before You Begin (Safety First)
Always allow the engine and transmission to cool down before working on any components. Disconnect the battery before performing any electrical diagnostics or component replacements to prevent accidental shorts or injury. Use proper jack stands when lifting the vehicle.
Common Symptoms
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission slipping
- Transmission stuck in a single gear (limp mode)
- Delayed engagement of gears
- Reduced fuel economy
Common Causes
- Short to voltage in the Shift Solenoid B control circuit wiring
- Faulty Shift Solenoid B
- Corroded or damaged connector for Shift Solenoid B
- Faulty transmission control module (TCM) or powertrain control module (PCM) (less common)
Frequently reported on: General/Universal
Diagnostic Steps
- Inspect the wiring harness and connectors for the Shift Solenoid B for any visible damage, frayed wires, or corrosion. Repair as needed.
- Check for proper voltage at the Shift Solenoid B connector using a multimeter, following your vehicle's service manual specifications.
- If accessible, perform an electrical resistance test (ohm test) on the Shift Solenoid B itself to ensure it's within manufacturer specifications.
- Clear the code and test drive the vehicle to see if the problem recurs.
- If the wiring and solenoid test good, and the problem persists, consider replacing the Shift Solenoid B.
👨🔧 When to Call a Professional
If after checking the wiring and connector for damage or corrosion, the issue persists, or if you suspect the shift solenoid B is located internally within the transmission, it is best to consult a professional transmission specialist. Internal transmission work requires specialized tools and expertise.
Commonly Asked Questions
Can I drive with a P0977 code?
Driving with a P0977 code is not recommended as it can lead to erratic shifting, potential transmission damage, or leave you stranded due to limp mode.
Is P0977 always a bad shift solenoid?
Not always. While a faulty shift solenoid is a common cause, the code indicates a "control circuit high," meaning the issue could also be in the wiring, connector, or even the PCM (though less common).
How expensive is it to fix P0977?
The cost can vary widely. If it's an external solenoid and simple wiring, it might be a few hundred dollars. If the solenoid is internal and requires extensive transmission disassembly, it could be over a thousand dollars.
How do I locate Shift Solenoid B?
The location of Shift Solenoid B varies by vehicle make and model. It can be found inside the transmission pan on the valve body or sometimes externally mounted on the transmission case. Consult your vehicle's service manual for the exact location.
Does replacing the transmission fluid help with P0977?
While regular transmission fluid maintenance is crucial for transmission health, simply replacing the fluid is unlikely to resolve a P0977 code, as it indicates an electrical control circuit issue, not typically a fluid quality problem.