P0979
UniversalShift Solenoid C Control Circuit Low means the Powertrain Control Module (PCM) has detected a low voltage condition in the control circuit for shift solenoid C.
Medium SeverityThis code indicates an electrical issue with Shift Solenoid C, often resulting in the transmission not shifting correctly or going into limp mode. A low voltage signal prevents the transmission from engaging or disengaging gears as commanded, impacting vehicle drivability.
⚠️ Before You Begin (Safety First)
Always practice caution when working on a vehicle. Ensure the vehicle is on a level surface and securely supported by jack stands if lifting. Allow the engine and transmission to cool down before handling components. Disconnect the battery before performing any electrical repairs to prevent accidental shorts or injury.
Common Symptoms
- Check Engine Light illuminated
- Transmission struggles to shift gears
- Transmission stuck in a single gear (limp mode)
- Delayed or harsh shifts
- Reduced fuel economy
- Vehicle may not move at all
Common Causes
- Faulty Shift Solenoid C
- Open or short in the shift solenoid C control circuit wiring
- Corroded or loose electrical connectors
- Low transmission fluid level or dirty fluid (indirectly leading to solenoid issues)
- Internal transmission mechanical failure
- Faulty Powertrain Control Module (PCM)
Frequently reported on: General/Universal
Diagnostic Steps
- Check transmission fluid level and condition, topping off or changing if necessary.
- Visually inspect wiring and connectors for Shift Solenoid C for damage, corrosion, or loose connections.
- Use a multimeter to check for proper voltage and continuity in the shift solenoid control circuit.
- Clear the code and test drive the vehicle to see if the code returns.
- If accessible externally, consider replacing Shift Solenoid C.
👨🔧 When to Call a Professional
If basic electrical checks do not reveal an obvious fault, or if the problem persists after replacing the solenoid, it's time to consult a professional transmission specialist. Internal transmission diagnostics and repairs can be complex and require specialized tools.
Commonly Asked Questions
Can I drive with a P0979 code?
It is not recommended to drive extensively with a P0979 code. Driving with transmission shifting issues can cause further damage to the transmission or lead to unsafe driving conditions.
Where is Shift Solenoid C located?
Shift solenoids are typically located inside the transmission valve body. In some vehicles, they might be externally accessible, but often require removing the transmission pan to access them.
How can I test Shift Solenoid C?
You can test the solenoid's resistance with a multimeter. Consult your vehicle's service manual for the correct resistance specifications. An open circuit or a reading significantly outside the specification indicates a faulty solenoid.
Is replacing a shift solenoid a difficult DIY repair?
It can be challenging. Accessing the solenoid often requires dropping the transmission pan and dealing with transmission fluid, which can be messy. Proper cleanliness and torque specifications are crucial during reassembly.
Could a P0979 code be caused by low transmission fluid?
While low fluid won't directly cause a 'circuit low' code, extremely low or dirty fluid can indirectly stress the transmission and its components, potentially contributing to solenoid failure or hindering its operation. Always check fluid first.