What it means
The control module detects a low electrical level in the shift solenoid C control circuit.
At a glance
- Usually lights the check-engine light
How it works
Shift solenoid C is an electrically operated valve that routes fluid within the transmission to help produce gear changes. The control module monitors the electrical level in the C control circuit and sets P0979 when that level is lower than expected. A short to ground, chafed control wire, or poor terminal contact can pull the C circuit low.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Capture freeze-frame data and review live transmission data to identify when the solenoid C circuit fault appeared.
- Inspect the C circuit harness for chafing, crushed insulation, or contact with grounded metal.
- Check solenoid C connector pins for corrosion, looseness, or poor contact that could lower the circuit signal.
- Use the wiring diagram to test the C control wire for a short to ground and inspect its full accessible run.
- Test solenoid C and the circuit connections against the manufacturer’s specification before replacing the valve.
- Evaluate the transmission control module only after the connector, wiring, and solenoid C pass their checks.
Common fixes
- Clean or repair corroded or loose terminals at the solenoid C connector.
- Repair chafed insulation or a C control wire shorted to ground.
- Replace shift solenoid C if it fails the specified electrical test.
- Repair or replace the transmission control module if testing confirms an internal control fault.
Can I keep driving?
Avoid hard acceleration and long trips if shifts are abnormal, and stop if the vehicle slips or loses drive. Continued driving with solenoid C’s circuit low can worsen shift problems and transmission wear.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.